Molecular-targeted therapy toward precision medicine for gastrointestinal caner: Current progress and challenges.

Core Tip: Outcomes in metastatic gastrointestinal (GI) cancer are improving with the better understanding and use of targeted therapies. Herein, a review of the literature and recent conference presentations was conducted regarding the topic of targeted therapies for precision medicine in GI cancer. This article clarifies the current evidence for targeted therapies in GI cancer by evaluating the latest data regarding anti- epidermal growth factor receptor, human epidermal growth factor receptor 2, vascular endothelial growth factor, phosphatidylinositol-3-hydroxykinase/protein kinase B, tumor growth factor-β, mesenchymal-epithelial transition, wireless network technology, poly (ADP-ribose) polymerase, and immunotherapies.

INTRODUCTION

In recent years, molecular-targeted agents that inhibit tyrosine kinase have been approved and have become a standard therapy for various cancers. Many of these drugs exert an antitumor effect by inhibiting the activity of the abnormal tyrosine kinase resulting from a genetic aberration. The use of agents against actionable gene mutations has shown a significantly higher response rate as well as longer survival compared to conventional chemotherapy in certain cancers[ 1 ]. For example, precision therapeutic attempts have markedly altered the management of advanced non-small-cell lung cancer (NSCLC). NSCLC harboring epidermal growth factor receptor (EGFR) mutation and anaplastic lymphoma kinase (ALK) fusion can be treated with anticancer drugs that target the aberrant gene products[ 2 ]. Today, patients with NSCLC survive for 3-4 years with a sequential use of effective targeted therapies, compared to 1-year survival for those without targetable mutations. There is relatively fewer evidence supporting the use of matched molecular-targeted agents as a treatment for gastrointestinal (GI) cancer[ 3 ].

For patients with gastric cancer (GC), anti-human epidermal growth factor receptor 2 (HER2) and anti-vascular endothelial growth factor (VEGF)-targeted therapies have become a standard therapeutic regimen. HER2-targeted therapy for patients with HER2-positive GC has been shown to provide better therapeutic survival than conventional chemotherapy, demonstrating that HER2-targeted therapy is a meaningful step forward to achieve precision therapy[ 1 ]. Similarly, United States National Comprehensive Cancer network guidelines recommend investigating the RAS [karst and national regulatory authorities (KRAS and NRAS)] mutation status in colorectal cancer (CRC) patients for the potential use of inhibitors for epidermal growth factor receptor mutations. Due to the ineffectiveness of anti-EGFR therapy for CRC patients with BRAF mutations, the identification of the BRAF mutation status was also recommended[ 4 ].

In this section, we outline the current advances of molecular-targeted drugs which are required for the advancement of precision medicine in GI cancer.

LITERATURE SEARCH

We first conducted a search of the PubMed database for English articles using the medical subject heading terms in combination with "gastrointestinal cancer," "esophageal cancer," "gastric cancer," "colorectal cancer," "molecular targeted therapy," and "precision medicine." Relevant articles from experimental studies and clinical trials since 1989 were selected, as well as articles related to the disease processes. Articles that did not deal with the precision medicine of GI cancer were excluded from this review. Liver and pancreatic cancer and GI stromal tumors were not covered in this review due to the limited scope of the topic.

TARGETING EGFR

EGFR, also known as ErbB1/HER1, belongs to the ErbB family that also includes ErbB2/HER2/Neu, ErbB3/HER3, and ErbB4/HER4[ 5 ]. Driven largely by its role in promoting cell proliferation and opposing apoptosis, the EGFR has been vilified as a proto-oncogene. These EGFR mutation and/or overexpression activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK- extracellular signal-regulated kinase (ERK) pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, and is the target of multiple cancer therapies currently adopted in the clinical practice[ 5 ]. Panitumumab and cetuximab are major EGFR monoclonal antibodies (mAbs) approved for the treatment of RAS wild-type metastatic (m) CRC. Because of the clinical significance of hot-spot KRAS mutations (codons 12 and 13) in patients with advanced CRC to anti-EGFR therapy resistance, KRAS mutation testing has become obligatory testing before managing anti-EGFR therapy[ 6 , 7 ]. To date, trifluridine/tipiracil (TAS-102) and regorafenib are the only last-line treatment options for mCRC, based on an improvement in median overall survival (OS) in randomized clinical trials. Nimotuzumab, a recombinant humanized mAb against human EGFR, demonstrated blocking ability against the binding of epidermal growth factor and tumor growth factor-alpha (TGF-α) to EGFR. Currently, a Phase III trial comparing paclitaxel plus cisplatin in combination with either nimotuzumab or placebo as the first-line treatment for patients with metastatic esophageal squamous cell cancer (ESCC) is under investigation in China ( NCT02611700 ).

Simultaneous blocking of the entire EGFR family might improve therapeutic efficacy. Three phase II clinical trials are evaluating the combination of afatinib with chemotherapy. One study analyzes afatinib in combination with cisplatin and 5-fluorouracil (5-FU) as a first-line treatment for advanced GC ( NCT01743365 ). The combination of afatinib and paclitaxel has been launched in patients with EGFR-positive GC as a second-line treatment ( NCT02501603 ), and another phase II study compared afatinib in combination with paclitaxel vs paclitaxel alone in refractory esophagogastric cancer (EC) ( NCT01522768 ). Poziotinib, formerly known as HM781-36B, is an irreversible pan-HER tyrosine kinase inhibitor (TKI) that targets EGFR, HER2, and HER4. Poziotinib is currently being investigated in a global phase II clinical trial which is expected to evaluate the efficacy of poziotinib in patients with EC, GC, or CRC who have failed two or three lines of treatment ( NCT03770988 , NCT01746771 , and NCT04172597 ).

However, despite appropriate patient selection based on molecular testing, secondary resistance to anti-EGFR antibodies will occur in several patients[ 8 ]. Multiple studies have thus focused on exploring resistance mechanisms. One of the most familiar mechanisms of acquired resistance to EGFR blockade in mCRC are mutations in the extracellular domain (ECD) of the EGFR gene[ 9 ]. Sym004, a mixture of two anti-EGFR mAbs, i.e. , futuximab and modotuximab, binds to nonoverlapping epitopes in EGFR ECD III, leading to more completely and durable pathway inhibition. The most significant information obtained from the analysis of the circulating free deoxyribonucleic acid (DNA) in mCRC patients treated with anti-EGFR agents is that resistance to these drugs is likely to be multiclonal rather than monoclonal in the majority of cases.

Several studies have presented some concomitant genomic alterations in patients who show progressing disease while they are being treated with anti-EGFR drugs. Patients were found to carry mutations in KRAS, NRAS, BRAF, EGRF, and MEK1 but also amplification of ERBB2, MET, FLT3, and KRAS [ 10 - 14 ]. These aberrant alterations result in resistance to anti-EGFR therapy mainly through a constitutive activation of EGFR downstream signaling pathways in spite of EGFR blockade.

BRAF mutation in CRC patients results in poor prognosis and resistance to treatment, leading to the need for a combination of multimolecular strategies. Mutations in BRAF, which are detected in approx. 10% of CRC patients overall, are mutually exclusive of KRAS mutations and occur more frequently in patients with mismatch repair (MMR) deficiency[ 15 ]. The most common BRAF mutation is valine (V) 600 glutamic acid (E), which results in an amino acid change from V to E, leading to a constitutive activation of BRAF by mimicking tyrosine kinase phosphorylation[ 16 ]. The results of several experiments implied that anti-EGFR therapy is not effective for mCRC patients with BRAF V600E-mutation[ 17 , 18 ]. Unfortunately, the BRAF inhibitor vemurafenib failed to reveal efficacy as a single agent in BRAF-mutated mCRC[ 19 ].

Based on the evidence that BRAF inhibition disrupts a negative feedback loop through EGFR and facilitates cellular proliferation, combined therapy consisting of both a BRAF inhibitor and an EGFR inhibitor would provide complemental benefit in patients with BRAF V600E-mutated mCRC[ 20 ]. A clinical study investigating the combined inhibition of BRAF V600E with vemurafenib and EGFR with cetuximab + irinotecan in BRAF V600E-mutated mCRC patients is underway ( NCT02164916 ).

The serine/tyrosine/threonine kinase MEK plays an important role in the RAS/RAF/MEK/ERK cell signaling pathway, which is frequently dysregulated in human cancers. A phase II study of selumetinib (AZD6244; ARRY-142866) (a tyrosine kinase inhibitor of MEK) + docetaxel as second-line chemotherapy for patients with GC is underway. Selumetinib + docetaxel revealed useful efficacy and tolerable safety in GC patients with a MEK signature or RAS gene alterations. Novel treatment combinations of BRAF and MEK inhibitors have started to demonstrate activity in early-phase trials of BRAF V600E mutant CRC.

DNA MMR deficiency is recognized as being predictive of benefit from immune checkpoint inhibitors, which have now been approved for use in later lines of treatment in this molecular subgroup of CRC. The triple inhibition of EGFR, BRAF, and MEK was evaluated by using panitumumab, dabrafenib, and trametinib, respectively, and the treatment proved to be a tolerable and promising therapeutic strategy for BRAF V600E-mutant CRC, resulting in the overall response rate (ORR) of 21%, and median progression-free survival (PFS) of 4.2 mo[ 21 ].

TARGETING HER2

The overexpression of HER2 has been implicated in resistance to anti-EGFR therapy via aberrant MEK-AKT pathway activation[ 22 ]. Dual HER2 inhibition with trastuzumab and lapatinib in patients with HER2-amplified, KRAS wild-type metastatic CRC who are resistant to standard therapies, including EGFR-targeted agents, demonstrated that dual HER2 blockade can produce objective responses[ 23 ]. These findings suggested a need for continued exploration to find viable treatment options for HER2-positive CRC[ 23 ]. Similarly, trastuzumab and pertuzumab demonstrated a 23% response rate and 69% disease control rate in the colorectal arm of a basket study[ 24 ].

HER2-targeted therapy for patients with HER2-positive GC who progressed on trastuzumab-based therapy is still challenging. Fam-trastuzumab deruxtecan (DS-8201a), a HER2-directed antibody and DNA topoisomerase I inhibitor conjugate, showed an acceptable safety profile and promising antitumor activity in salvage-line subjects with HER2-positive GC patients who previously received trastuzumab[ 25 ]. The randomized, phase II, multicenter, open-label, destiny-Gastric01 study is ongoing ( NCT03329690 ). The primary purpose of this trial is to compare the efficacy and safety of DS-8201a and physician's choice treatment in HER2-positive GC. Similarly, the destiny-CRC01 trial is under evaluation; its main objective is to test the safety and effectiveness of DS-8201a for patients with HER2-positive CRC ( NCT03384940 ). Ongoing studies are evaluating trastuzumab + pertuzumab vs cetuximab and irinotecan ( NCT03365882 ), and tucatinib (ONT-380; a highly selective small molecule inhibitor of Her-kinase) and trastuzumab in patients with HER2-positive, previously treated advanced CRC ( NCT03043313 ).

TARGETING ANGIOGENESIS

Angiogenesis plays a pivotal role in the growth, metastasis, and ascites formation of malignancies. The overexpression of angiogenic factors such as VEGF, fibroblast growth factor (FGF), and platelet-derived growth factor (PDGF) was reported to be correlated with the tumor development and poor survival of GI cancer patients[ 26 ]. The OS for GI cancer increased to 3 years with the application of anti-VEGF monoclonal antibodies[ 27 ]. Three clinical trials comparing patients treated with fluorouracil/ Leucovorin alone or in combination with bevacizumab showed improved response rates and OS[ 28 ]; however, the therapeutic effect of anti-VEGF therapy in mCRC patients was reduced for several months due to acquired resistance. During bevacizumab exposure, VEGF-A is decreased, instead of increased levels of vascular endothelial growth factor receptor 1 (VEGFR1) which result in drug resistance. Hepatocyte growth factor (HGF)-ligand inhibition and silencing HOXB9 is expected to be a promising approach to regulate this resistance[ 29 , 30 ].

Similarly, the anti-VEGF drug ramucirumab in combination with chemotherapy in the treatment of advanced GC significantly improved the ORR and prolonged the PFS and OS compared to chemotherapy alone[ 31 ]. The rainbow subgroup analysis of patients who received prior trastuzumab therapy showed that the OS was prolonged in the second-line ramucirumab + paclitaxel combination group (11.4 mo; 95%CI: 7.0-17.9) vs the placebo + paclitaxel group (7.0 mo; 95%CI: 3.4-14.6)[ 32 ]. In 2012, regorafenib, a multikinase inhibitor, was approved by the United States food and drug administration (FDA) for the treatment of patients with mCRC who have progressed on standard chemotherapies[ 33 ]. Significant improvement in the OS of chemo-refractory KRAS wild-type mCRC patients was observed when regorafenib was administered before cetuximab +/− irinotecan, compared to the reverse treatment sequence (HR: 0.61, P = 0.0293)[ 34 ]. Regorafenib has shown promising activity in GC patients in the integrate phase II trial[ 35 ]. Thus, blockage of the interaction of multiple growth factors with their receptors might improve therapeutic efficacy.

Vandetanib (ZD6474) is an oral tyrosine kinase inhibitor of VEGFR-2, VEGFR-3, RET, and EGFR. A Phase I trial demonstrated that the administration of vandetanib with a chemotherapy regimen as well as concurrent radiation therapy is feasible in the neoadjuvant setting for the treatment of locally advanced esophageal cancer[ 36 ]. Apatinib is an orally bioavailable TKI that selectively inhibits VEGFR-2, c-Kit and Src, which has been approved by China's national medical products administration (formerly the China food and drug administration) for third-line treatment of patients with GC[ 37 ]. The phase II clinical trial of apatinib monotherapy for chemotherapy-refractory mCRC revealed improved survival outcomes over the historical control expected from a placebo or best supportive care[ 38 ].

In contrast, apatinib may be an option to improve the chemosensitivity of paclitaxel and 5-FU in the treatment of GC[ 39 ]. Axitinib, a first-generation anti-VEGFR TKI with high potency against VEGFRs, platelet-derived growth factor receptor (PDGFR) and c-KIT, has been approved by the FDA for the treatment of renal cell carcinoma[ 40 ]. In phase II trials, the median PFS was significantly increased in the axitinib group compared to the placebo group (4.9 mo vs 3.1 mo; P = 0.0116) for patients with first-line mCRC, suggesting that axitinib is a promising candidate for the maintenance treatment of mCRC[ 41 ]. Fruquintinib, a novel oral TKI of VEGFR-1, -2 and -3, afforded significantly superior median OS (HR: 0.65, P < 0.001) and median PFS (HR: 0.26, P < 0.001) compared to placebo in patients with chemo-refractory mCRC, and it demonstrated the benefit of VEGFR inhibition in the latter lines of mCRC treatment[ 42 ].

Bemarituzumab (FPA144), a fucosylated mAb directed against FGFR2b, can be safely administered to patients with advanced gastroesophageal adenocarcinoma. In a phase I study of bemarituzumab (FPA144) treatment for patients with advanced FGFR2b-selected gastroesophageal adenocarcinoma, stable disease was the best observed response in 13 additional patients, leading to an overall disease control rate [ i.e. , partial response (PR) + stable disease] of 64.3% (95%CI: 44.1%-81.4%) in the subgroup with high FGFR2b overexpression[ 43 ]. A randomized double-blinded phase II study with a primary endpoint of overall survival with or without bemarituzumab in addition to mFOLFOX6 for GC is now underway ( NCT03694522 ).

To date, erdafitinib was developed for treating patients with advanced or metastatic urothelial cancer with FGFR3 or FGFR2 alterations, accounting for 15%-20% of patients[ 44 ]. Erdafitinib is now being evaluated in a multicenter phase II clinical trial which is expected to determine the efficiency of erdafitinib in ECC and GC patients with FGFR translocation or mutation ( NCT02699606 ).

TARGETING THE PI3K/ AKT/MTOR PATHWAY

The PI3K pathway, discovered over 20 years ago, plays an important role in a variety of cellular activities. Emerging data show that the PI3K/AKT/mechanistic target of rapamycin (mTOR) cascade is involved in the development of GI cancer[ 45 ]. Despite extensive efforts evaluating the value of PI3K/AKT/mTOR inhibitors in GI cancer ( e.g. , BEZ235, NVP-BEZ235, OSI-027, MK-2206, KRX-0401, BYL719, and BKM120), several significant problems remain to be clarified regarding the molecular mechanisms underlying the targeting of the PI3K/AKT pathway in GI cancer and overcoming resistance. The selection of patients who could obtain the greatest advantage from treatment as well as combination therapies with agents targeting another pathway would be important. Interestingly, a phase I/II trial examined the efficacy of everolimus, an inhibitor of mTOR, in combination with mFOLFOX6 + bevacizumab as a first-line treatment for mCRC patients; the response rate was assessed based on the expression of phosphatase and tensin homolog (PTEN)[ 46 ].

A phase Ib clinical trial evaluating triple-drug combinations of cetuximab, encorafenib ( BRAF inhibitors), and a PI3Kα inhibitor, alpelisib, demonstrated more convincing efficacies than "targeted doublets"[ 47 ]. The ORR was 53% in the whole population, and it was superior (86%) in the patients with PTEN expression below the threshold ( P = 0.03). A phase III randomized, double-blind study of paclitaxel with and without everolimus failed to show improved outcomes with the addition of everolimus. However, everolimus significantly prolonged the PFS of the patients pretreated with taxane ( P = 0.03)[ 48 ]. BYL719 is a selective PI3Kα inhibitor that was reported to be equipotent against the wild-type and the most common somatic mutations of PI3Kα[ 49 ]. BYL719 has shown markedly selective efficacy in PIK3CA mutants. A multi-center, open-label phase II biomarker-driven umbrella trial is in progress in Korea, investigating ECC ( NCT03292250 ): BYL719 is selectively applied for the patients with relevant genetic alterations including a PI3K pathway alteration revealed by next-generation sequencing.

AZD5363 is a novel AKT kinase inhibitor that has potential based on the genetic status of PIK3CA, PTEN[ 50 ]. A phase II study of AZD5363 in combination with paclitaxel in patients with GC harboring a PIK3CA mutation or amplification as a second-line chemotherapy was launched in 2015 ( NCT02451956 ). ABI-009 (nab-rapamycin) is a nanoparticle form of human albumin-bound rapamycin with a mean particle size of approx. 100 nm, developed with a proprietary nanoparticle albumin-bound technology[ 51 ]. In CRC, a multicenter open-label phase I/II trial to investigate the efficacy of ABI-009 in combination with mFOLFOX6 and bevacizumab as first-line therapy is underway ( NCT03439462 ).

TARGETING THE TGF-Β PATHWAY

TGF-β is a cytokine involved in both physiological and pathological processes including tumorigenesis and cancer spreading[ 52 ]. TGF-β signaling mediates immune/inflammatory responses and tumor microenvironments throughout the development of a tumor. It also regulates tumor growth, the epithelial-mesenchymal transition, and cancer cell stemness[ 52 ]. In the majority of CRC and GC patients with microsatellite instability (MSI), inactivating mutations in the TGFBR2 gene were shown[ 53 ]. Mutations in Smad4, which have been identified in > 30% of CRC patients, have been said to disrupt TGF-β signaling[ 54 ].

Thus, participates in the development of GI cancers, and management targeting the TGF-β signaling pathway may be effective for the treatment of GI cancers. M7824 (MSB0011359C) is a first-in-class bifunctional fusion protein composed of the extracellular domain of two TGF-β receptor 2 (TGF-βR2) molecules that serve as a TGF-β sequestering or trap molecule fused to a fully humanized mAb against PD-L1[ 55 ]. M7824 simultaneously blocks the PD-L1 and TGF-β pathways of immune evasion. A phase 1 trial of M7824 with 19 patients with heavily pretreated advanced solid tumors, including CRC, revealed a manageable safety profile comparable to other anti-PD-1/PD-L1 antibodies[ 56 ] ( NCT02517398 ).

Even though few drugs targeting TGF-β have exhibited efficiency in clinical trials, the future of TGF-β pathway-based strategies against GI cancers is encouraging from these inspiring clinical trials[ 57 ]. Vactosertib (EW-7197) is a potent, orally active and ATP-competitive TGFBR1 and ALK inhibitor. A phase 1b/2a multicenter study to assess the safety, tolerability, pharmacokinetics, and antitumor activity of vactosertib in combination with pembrolizumab in patients with mCRC or GC is currently underway ( NCT03724851 ).

TARGETING HGF/ C-MET

C-MET, a kinase receptor for HGF, is well known for its roles in driving tumorigenesis. HGF/ mesenchymal-epithelial transition (c-MET) is also thought to promote the progression of tumorigenesis[ 58 ]. In GC, elevated c-MET expression is also a predictor of poor OS compared to c-MET negative tumors[ 59 ]. Several c-MET inhibitors have been developed as anticancer drugs in GC therapy. A phase I study of the c-Met tyrosine kinase inhibitor SAR125844 in Asian patients with MET-amplified solid tumors, including GC, demonstrated that among 19 patients with MET-amplified solid tumors, with the administration of 570 mg/m 2 of SAR125844, two GC patients had partial responses, seven patients had stable disease (six GC and one renal cancer), and 10 patients had progressive disease[ 60 ].

An ongoing phase Ib clinical trial is currently evaluating the efficacy and safety of INC280, an orally administered c-Met inhibitor, in combination with cetuximab in patients with c-Met-positive metastatic CRC whose disease progressed on cetuximab or panitumumab treatment ( NCT02205398 ). A potent and selective MET inhibitor, savolitinib, is being investigated in a phase II trial in patients with MET-amplified CRC (NCT03593641). More and more c-MET inhibitors have been found to have antitumor activity in GI cancer, but many drug studies have remained at a nonclinical stage.

TARGETING THE WNT PATHWAY

Wnt proteins are cysteine-rich glycoproteins that bind to the extracellular domain of frizzled receptor and lipoprotein receptor-related protein 5/6. Wnt signaling mediates diverse cellular processes, including cell fate, movement, polarity, and organogenesis[ 61 ]. In recent years, the understanding of the role of Wnt secretion in tumor initiation has developed and revealed novel therapeutic targets. Mutations of RNF43 and R-spondin fusion proteins, which mutually exclusively occur with APC mutations in CRC, were subsequently identified as a predictor of effective therapy targeting Wnt secretion[ 62 ]. Based on these results, a phase I/II trial of LGK974 was initiated for patients with mCRC harboring mutations of RNF43 or R-spondin fusions. In addition, a novel orally available porcupine inhibitor ( i.e. , ETC-1922159) that was found to prevent the growth of R-spondin-fusion-positive CRC is being assessed in a clinical trial ( NCT02521844 ). A current phase I/II study is evaluating the orally bioavailable and specific porcupine inhibitor WNT974 in patients with mCRC with BRAF V600 and ring finger protein 43 mutations or RSPO fusions, in combination with a BRAF inhibitor and anti-EGFR agent to mitigate acquired resistance through the Wnt-β-catenin pathway ( NCT02278133 ).

Foxy-5, a Wnt-5a agonist, is a mimicking peptide of Wnt-5a and a non-canonical member of the Wnt family which impairs the migration and invasion of epithelial cancer cells[ 63 ]. Foxy-5 is currently being tested in a resected CRC setting in the Neo Fox trial, in which standard therapy (surgery + FOLFOX 6-month regimen) + neo-adjuvant administration of Foxy-5 prior to and following surgery is being compared to standard therapy alone in patients with Wnt-5a low CRC ( NCT03883802 ). Dickkopf-1 was identified as a secretory protein that can inhibit the Wnt signaling pathway by competitively binding to Wnt ligand-receptor LRP5/6. An ongoing phase IIa study is evaluating the use of DKN-01 in combination with tislelizumab and chemotherapy as first-line or second-line therapy in patients with GC ( NCT04363801 ).

TARGETING POLY (ADP-RIBOSE) POLYMERASE

Chromosomal instability is the hallmark of the chromosomal instability subtype of GC according to the cancer genome atlas classification. The poly (ADP-ribose) polymerases are a family of enzymes that are activated by DNA damage and facilitate DNA repair[ 64 ]. A defect in DNA repair may lead to the loss of chromosomes associated with sensitivity to PARP inhibitors[ 65 ]. In preclinical studies, the PARP inhibitor olaparib was active against GC cell lines with low levels of ataxia telangiectasia mutated (ATM) kinase, which is an activator of the DNA damage response[ 65 ]. Although the advantage of combining olaparib with paclitaxel therapy for metastatic GC was not shown in a phase III trial[ 66 ], these trials involved only a few patients with low levels of ATM. A trial evaluating the safety and activity of olaparib combined with durvalumab in patients with advanced-stage GC is underway ( NCT02734004 ) . A phase I/II pilot study was prepared to analyze the efficacy of olaparib in combination with ramucirumab in patients with metastatic, recurrent or unresectable GC ( NCT03008278 ), and a phase II trial designed to assess the efficacy and safety/tolerability of olaparib in patients with advanced EC is currently ongoing ( NCT03829345 ).

As well, a phase II non-randomized open-label study to evaluate temozolomide in combination with olaparib in patients with MGMT promoter hypermethylated advanced CRC is now recruiting ( NCT04166435 ). Rucaparib (Rubraca ® ) is a small-molecule PARP inhibitor with potent activity against PARP-1, -2 and -3. It is approved in the United States and the EU for the treatment of patients with BRCA-mutated ovarian cancer who have failed upfront standard chemotherapy[ 67 ]. A phase I/II trial of rucaparib in combination with ramucirumab with or without nivolumab in patients with advanced GC who have been treated with two or more lines of chemotherapy is in progress ( NCT03995017 ).

TARGETING ANAPLASTIC LYMPHOMA KINASE

ALK, which is also known as ALK tyrosine kinase receptor, is a tyrosine kinase encoded by the ALK gene. ALK is constitutively activated by fusion events, which leads to cellular transformation and the facilitation of survival and growth through downstream signaling[ 68 ]. Gene fusion is the most frequent molecular alteration occurring in this gene across different tumor types including GI cancer. ALK, ROS1, and NTRK fusions occur in 0.2%-2.4% of cases of CRC. Entrectinib is an oral inhibitor of TRK A/B/C, ROS1, and ALK. The results of two phase I studies with 119 patients have been published; 18 of these patients had GI cancer[ 69 ]. The ORR was 57% in the ALK-rearranged solid tumors, which included CRC. Thus, targeted agents may provide clinical benefit to patients with rare fusions . A l though their incidences are minor, the presence of gene fusions is easily detectable by a liquid biopsy, and further research is thus worthwhile.

OTHER CANDIDATES

Claudin (CLDN) 18.2 is an isoform of claudin proteins, which play a role in maintaining tight cell junctions. The identification of CLDN 18.2 in GC became a potential target with the ensuing development of a mAb against CLDN 18.2, i.e. , zolbetuximab (formerly known as IMAB362). More recently, the results of the randomized phase II fast study demonstrated that the combination of claudiximab + EOX significantly increased the response rate and improved the PFS and OS of patients with higher CLDN 18.2 expression. Monotherapy with zolbetuximab, a chimeric IgG1 mAb that binds to CLDN 18.2, showed superior antitumor activity in patients with CLDN18.2-positive advanced gastric or gastroesophageal junction (GEJ) adenocarcinomas[ 70 ].

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors are orally bioavailable drugs that have been explored as anticancer agents. These agents directly block the activity of the cyclin D-CDK4/6 holoenzyme, which leads to the inhibition of the growth of sensitive tumor cells. The CDK4/6 inhibitors specifically block cell-cycle progression from the G1 to the S phase of the cell cycle. There is an ongoing phase II trial comparing palbociclib, an oral inhibitor of CDK4/6 + binimetinib vs TAS-102 for the treatment of patients with KRAS and NRAS mutation-positive CRC ( NCT03981614 ). Regarding GC, alvocidib , a flavonoid alkaloid CDK9 kinase inhibitor under clinical development for the treatment of acute myeloid leukemia, has been investigated in phase I and II trials. In patients with GC, the efficacy of alvocidib in combination with nivolumab or pembrolizumab is being tested ( NCT03311334 ).

Histone deacetylases (HDACs) have a key impact on chromatin remodeling and epigenetics, which makes their inhibitors a very attractive area of investigation. In hepatocellular carcinoma, epigenetic therapy with belinostat, a potent HDAC inhibitor, demonstrated that a 58% disease stabilization rate ( i.e. , CR + PR + SD) in tumors with high and low HR23B histoscores[ 71 ]. However, although the objective PR was 42%, the combination of vorinostat with capecitabine + cisplatin is not likely to show enhanced efficacy in comparison with standard fluoropyrimidine-platinum doublet regimens in patients with GC[ 72 ].

Napabucasin is a cancer stemness inhibitor that targets a number of oncogenic pathways, including the signal transducer and activator of transcription 3 pathway. Phase I/II studies have indicated the tolerability and antitumor activity of napabucasin in various types of cancer, including CRC. For example, a multicenter randomized phase II study (modulate) is in progress to assess the efficacy of the combination of nivolumab and BNC105 (a microtubule/tubulin inhibitor) and the combination of nivolumab and napabucasin to modulate the tumor microenvironment in patients with microsatellite-stable refractory CRC. A phase III study of napabucasin + standard therapy in GC and CRC is ongoing ( NCT02178956 , NCT3522649).

Notch pathway signaling is associated with several human cancers[ 73 ]. A role for Notch signaling in the maintenance of cancer stem cells has been presented in preclinical experiments and recently in clinical trials. CB-103, an orally active small-molecule inhibitor of the Notch transcription activation complex, is being investigated in a phase I/II trial in patients with refractory solid tumors, including CRC ( NCT03422679 ). Th e ubiquitin proteasome system plays an important role in the degradation of intracellular proteins involved in multiple cellular processes, including cell-cycle division, DNA repair, and the regulation of membrane receptors[ 74 ]. Bortezomib is one of the major components of proteasome inhibitors, with activity in multiple myeloma. Bortezomib/paclitaxel/carboplatin is currently being tested in patients with metastatic esophageal cancer and gastroesophageal adenocarcinoma ( NCT02912559 ).

Heat shock protein (Hsp) 90 serves as a chaperone protein that promotes the proper folding of proteins involved in a variety of signal transduction processes[ 75 ]. HSP90 has been demonstrated to play pivotal roles in tumor development and resistance to recently applied therapies. However, recent clinical trials using established inhibitors against HSP90 demonstrated limited clinical efficacy when the inhibitors were used as a monotherapy. These results suggest that combinations of the inhibitors with standard chemotherapeutic agents might improve the antitumor efficacy of the HSP90-inhibitors.

Luminespib is a representative HSP90 inhibitor that shows anticancer effects via binding to the ATPase domain of HSP90, causing a loss of chaperone functions. Luminespib is currently being investigated in a phase II clinical trial, which is expected to enroll 21 patients to evaluate the efficacy of luminespib + trastuzumab in patients with HER2-positive advanced GC who have received trastuzumab + chemotherapy as the first-line treatment ( NCT 01402401 ).

The hedgehog signaling pathway is an evolutionarily conserved pathway of signal transmission from the cell membrane to the cell nucleus[ 76 ]. The hedgehog signaling pathway plays a significant role in the normal embryonic development of invertebrates and vertebrates. Vismodegib, a first-in-class small molecule inhibitor of Hedgehog pathway signaling was approved by the FDA and the European Medicines Agency for the treatment of adults with basal cell carcinoma. The phase II trial to investigate the efficacy of vismodegib in GC patients with SMO overexpression is ongoing ( NCT03052478 ).

THE DEVELOPMENT OF IMMUNOLOGY

One of the fundamental avoidant mechanisms of cancer cells is the alteration of the host immune system. Immunotherapy has been shown to be aggressive in tumors containing a high mutation as confirmed in melanoma and lung cancer[ 77 , 78 ]. An increased amount of mutations is responsible for the production of neoantigens, which leads to enhanced tumor immunogenicity. In MSI, frameshift mutations in protein-coding sequences retain the ability to produce a variety of peptides with potential neoepitopes acknowledged as foreign substances by the immune system[ 79 ]. The immune checkpoint receptor programmed death-1 (PD-1) is a co-inhibitory molecule that is physiologically expressed on immune cells such as T and B lymphocytes and myeloid cells providing the signal for the termination of immune system activity. PD-1 receptor has two natural ligands, programmed death-ligand 1 (PD-L1) and PD-L2, which can be expressed in immune cells as well as tumor cells; this represents a potential mechanism of immune surveillance escape[ 79 ].

In GC, subtypes such as MSI-H tumors harboring multiple neoantigens resulting from MMR gene deficiency as well as Epstein-Barr virus (EBV)-positive tumors expressing PD-L1/L2 may serve as candidates for immunotherapy. It is suspected that roughly one-third of all GC cases are potentially immunogenic. A recent randomized phase III trial, attraction-2 (ONO-4538-12), investigated treatment with nivolumab, a mAb targeting PD-1, after two or more previous chemotherapy regimens in advanced GC patients; the results demonstrated extended median overall survival compared to that associated with a placebo[ 80 ]. Based on that trial, nivolumab gained approval in Japan. The clinical effectiveness of using nivolumab alone or in combination with ipilimumab (a fully human IgG1 monoclonal antibody inhibitor of cytotoxic T-lymphocyte associated protein-4) in patients with chemotherapy-refractory advanced GC/GEJC was shown in the GC cohort of the phase I/II CheckMate-032 trial[ 81 ]. A previous study reported that a patient with EBV-infected GC achieved a robust response to treatment with the anti-PD-L1 antibody avelumab[ 82 ].

ARID1A alterations are significantly associated with EBV infection, which in turn leads to longer PFS after anti-PD-1/PD-L1 immunotherapy, regardless of the microsatellite and tumor mutational burden status[ 82 ]. Another PD-1 antibody, pembrolizumab, also showed encouraging antitumor activity for PD-L1-positive advanced GC in phase II and III trials[ 83 , 84 ]. The ATTRACTION-3 trial, which was a phase III trial of the efficiency of nivolumab, revealed that nivolumab treatment resulted in significantly higher OS relative to chemotherapy (docetaxel or paclitaxel) in a PDL1-unselected population with EC[ 85 ]. Camrelizumab + apatinib in combination with liposomal paclitaxel and nedaplatin could be a new treatment option for patients with unresectable locally advanced or metastatic ESCC ( NCT03603756 ). Thus far, CRC has been a poor candidate for immunotherapy. Early studies are deficient in objective clinical responses to nivolumab among patients with unresectable mCRC. However, and increasing amount of evidence suggests the effectiveness of the application of a check-point inhibitor (CPI) in patients with MSI-H CRC[ 86 ].

Clinical trials investigating the combination of nivolumab + ipilimumab for patients with MSI-H demonstrated high response rates and encouraging PFS and OS at 12 mo, manageable safety, and meaningful improvements in key patient-reported outcomes[ 87 ]. Subsequently, there is growing attention regarding the use of a combination of CPI with chemotherapies or targeted therapies. The combined therapy of bevacizumab + atezolizumab revealed a clear significant effect for MSI-H patients in a phase III clinical trial ( NCT02997228 ). An ongoing trial is evaluating the safety and efficacy of the combination of regorafenib + nivolumab in patients with previously treated advanced gastric cancer or CRC (NCT32085012).

A better understanding of cancer immunotherapy agents that can provide prolonged survival in the microsatellite-stable (MSS) subgroup of GI cancer will contribute to the outcomes of this patient subset, which accounts for the majority of GI cancer patients. One approach to further improving GI cancer therapy is a vaccination with peptides alone, peptide-expressing viruses, peptide-loaded antigen-presenting cells, or the application of peptide-specific T cells. Traditionally, the advancement of such cancer vaccines started with peptides derived from tumor-associated antigens (TAAs), tumor-specific antigens, and cancer testis antigens. Several lines of evidence support neoantigens as important targets for immune responses. A phase I/II open-label study exploring the immune response to TAA CEA of a dendritic cell vaccination in patients with Lynch syndrome or CRC with MSI is ongoing ( NCT01885702 ).

Similarly, chimeric antigen receptor (CAR)-T cell immunotherapy enhances the immune cells' ability to eradicate cancer cells by reprogramming them to express CAR protein and selectively binding to the cancer cells. The efficacy of CAR-T cell therapy has been demonstrated in mouse models of mCRC and GC[ 88 ]. A phase I prospective nonrandomized controlled trial to investigate the safety and efficacy of the infusion of intraperitoneal EpCAM CAR-T cells for the treatment of advanced GC with peritoneal metastasis is now underway ( NCT03563326 ).

CLOSING REMARKS AND FUTURE PERSPECTIVE

This review has briefly summarized the current evidence and ongoing clinical trials regarding the application of targeted therapy in GI cancer in various settings. The goal of treating GI cancer is to provide the most effective approach across multiple lines of therapy for individual patients, using the tumor characteristics to inform the selection and sequencing of agents. In addition to EGFR and VEGF signaling, new molecular targets are being continuously detected, e.g. , MET, FGFR, ALK, TGF-β, WNT, PAPP, CDK, Hedgehog, CLDN18.2, and immune checkpoint inhibitors, which has prompted the development of new therapies. In the past few decades, evolving sequencing technologies have uncovered genomic, transcriptional, proteomic, and epigenetic details as never before. Numerous investigations of new GI cancer-targeted agents have been conducted with the goals of achieving better patient compliance, lower rates of adverse events, and more personalized treatment options.

Genomic profiling for optimum patient selection has great promise to guide future precision medicine applications for GI cancer. The specific use of TKIs should be planned based on the patients' genetic backgrounds, and the precise signaling pathway that induces the carcinogenic properties of the cells for a given cancer type should be identified. The targeted agents for GI cancer now being investigated in clinical trials are summarized in Tables 1 - 3 and Figure 1 .

Cancer cell growth, differentiation, and angiogenesis are thought to be mediated by multiple intracellular and cell-surface protein kinases with their downstream pathways. Multi-kinase inhibitors, which are agents that target several kinases or pathways simultaneously, have recently been developed for malignancies. Regorafenib and sorafenib are currently approved by the United States FDA for treating patients with CRC and renal cancer, respectively. Sorafenib, a broad-spectrum TKI targeting VEGFR2 and PDGFR as well as RET and RAF1, has been investigated in phase II trials, and the results have led to disease stabilization and encouraging PFS in patients with refractory EC[ 89 ].

In addition, as noted above, vandetanib, apatinib, axitinib and fruquintinib are currently being tested in GI cancer settings in clinical trial. Pazopanib is another TKI that targets VEGFR, PDGFR, FGFR, and C-kit; it emerged almost a decade after sorafenib. Pazopanib is being investigated in ongoing phase I/II studies in combination with chemotherapy in GC and CRC as first-line treatments ( NCT01716546 and NCT00387387 ). A large-scale phase III randomized trial was launched in 2008 with the primary endpoint of OS; it compared brivanib alaninate with or without cetuximab in patients with K-RAS wild-type tumors following failure of treatment with chemotherapy for mCRC ( NCT00640471 ). Similarly, there are several ongoing clinical trials in GI cancer evaluating the use of inhibitors targeting multi-kinases including VEGFR (sunitinib, lenvatinib, nintedanib, dasatinib, carbozantinib, surufatinib, sitravatinib, vorolanib, dovitinib, and telatinib) with or without cytotoxic agents.

Crizotinib, an oral ALK/MET/ROS1 inhibitor, prompted the development of ALK target therapy[ 90 ]. It became the first ALK inhibitor to be approved by the FDA for standard first-line therapy in patients with ALK-positive NSCLC. Crizotinib is also currently being investigated in a clinical trial evaluating the efficacy of poziotinib in patients with mCRC and ALK mutation who have failed two or three lines of therapy ( NCT03792568 ).

Multi-kinase inhibitors, which broadly inhibit cancer-related kinases, also carry the risk of inhibiting kinases whose function is unknown. Thus, along with their efficacy, multi-kinase inhibitors have been found to cause several unfavorite side effects such as proteinuria, stomatitis, diarrhea and hypertension, the latter of which were observed in more than half of the treated patients[ 91 ]. Future studies should continue to examine multi-kinase inhibitors toward the goal of achieving synergistic activity while minimizing toxicity.

In principle, combinatorial therapies that target a wide range of tumor biological functions (including cell proliferation, motility, apoptosis, and others) are considered an attractive option. The concurrent administration of several drugs that target different cellular drivers of tumor cells has been reported to be frequently beneficial over monotherapeutic approaches, due to their synergistic effect[ 92 ]. Moreover, combinatorial therapies can reduce the doses of the individual drugs and therefore prevent primary and secondary therapeutic resistance by down-regulating different metabolic factors[ 93 , 94 ]. Theoretically, a combination of TKIs that could doubly inhibit similar signaling pathways is thought to be ideal because it may prevent primary and secondary therapeutic resistance. For example, as noted above, dual HER2 inhibition is active in patients with CRC[ 23 ].

There are several ongoing studies including LJM716 + trastuzumab treatment for GC ( NCT01602406 ) and tucatinib + trastuzumab treatment for CRC. The triple inhibition of EGFR, BRAF and MEK demonstrated synergistic activity for BRAF V600E-mutant CRC[ 21 ] . Another strategy under development consists of a crosstalk inhibition of another class of drug. In melanoma, many successful new combinations use mAbs that inhibit immune checkpoints such as CTLA-4 or PD-1 receptors and MEK and BRAF inhibitors[ 95 ]. These combined therapies have shown enhanced anti-metastatic effects and enhanced antitumor immunity in clinical trials[ 96 ]. In mCRC, a phase III multicenter open-label three-arm randomized study (COTEZO IMblaze370) is underway to investigate the efficacy of cobimetinib + atezolizumab and atezolizumab monotherapy vs regorafenib.

The synergistic effects of immune checkpoint blockade and anti-angiogenesis approaches in cancer treatment are now attracting attention. Based on the interaction between tumor immunity and angiogenesis, it is speculated that anti-angiogenesis approaches might enhance the efficacy of immune checkpoint inhibitors. In the case of GI cancer, lenvatinib (a TKI that acts on a range of receptors including VEGFR, PDGFR, FGFR and RET) is currently being investigated in a global phase II clinical trial that will evaluate the efficacy of lenvatinib + pembrolizumab in patients with advanced GC or CRC who have failed two or three lines of therapy ( NCT03797326 ). As mentioned above, the combination of TKIs is ideal from a theoretical point of view. However, the achievement of its clinical application is not easy in light of the toxicity; RTKIs have specific toxicities that are related to the primary target kinases or an off-target effect or are caused by a specific metabolite of the kinase inhibitor. This may be prevented by a better determination of toxicity profiles of each drug before they are used in combination, in order to select the most specific TKIs[ 97 ]. Investigations of the synergistic properties of TKIs with other agents (such as a monoclonal antibody targeting PD-1) will likely contribute to the advancement of effective therapeutics with low toxicity, including tolerance for drug combinations, toward the achievement of better cancer therapy.

Collectively, the findings presented above are encouraging. Patients with GI cancer are living longer with the best treatment strategies, several of which could eventually be quite beneficial. Selected mutant gene profiles are eligible for target therapy. GI cancer is a heterogeneous disease with many diverse sets of alterations in tumor suppressor genes and oncogenes. The profiling of the entire spectrum of genetic changes based on advances in next-generation sequencing and whole-genome sequencing will provide a foundation that can be used to stratify patients in distinct molecular subclasses that suggest prognostic relevance and possible treatment advantages. However, many questions remain to be answered such as treatment scheduling, optimized dosages, and combinations with other agents. The identification of potential biomarkers that can predict the patients' clinical responses and the toxicities of these targeted therapies is challenging. Adverse events which may be caused by combined targeted agents and acquired resistance are additional research focuses for targeted drug advancement. Feasibility studies are necessary to develop well-designed randomized clinical trials that can evaluate the appropriate biomarkers, synergic effects, and degrees of toxicity.

CONCLUSION

Together, the above-described findings indicate that clinical trials designed based on patients' molecular profiles will lead to more personalized precision treatments for patients and better outcomes. Improved algorithms for the selection of immune checkpoint inhibitors or combination therapy should be established. These developments could facilitate precision medicine for patients with gastric cancer in the near future.

ACKNOWLEDGEMENTS

Tasuku Matsuoka conducted the literature search, drafted the initial manuscript, critically reviewed the manuscript, and approved the final manuscript as submitted. Masakazu Yashiro critically reviewed the manuscript, and approved the final manuscript as submitted.

Conflict-of-interest statement: There are not any financial or other interests regarding the submitted manuscript that might be construed as a conflict of interest.

Manuscript source: Invited manuscript

Peer-review started: January 14, 2021

First decision: February 14, 2021

Article in press: April 21, 2021

Specialty type: Oncology

Country/Territory of origin: Japan

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P-Reviewer: Li LW, Liu Y S-Editor: Zhang L L-Editor: A P-Editor: Li JH

1 Nie S Yang G Lu H Current Molecular Targeted Agents for Advanced Gastric Cancer Onco Targets Ther 2020 13 4075 4088 32494161 10.2147/OTT.S246412 PMC7229784

2 Ettinger DS Wood DE Aisner DL Akerley W Bauman J Chirieac LR D'Amico TA DeCamp MM Dilling TJ Dobelbower M Doebele RC Govindan R Gubens MA Hennon M Horn L Komaki R Lackner RP Lanuti M Leal TA Leisch LJ Lilenbaum R Lin J Loo BW Jr Martins R Otterson GA Reckamp K Riely GJ Schild SE Shapiro TA Stevenson J Swanson SJ Tauer K Yang SC Gregory K Hughes M Non-Small Cell Lung Cancer, Version 5.2017, NCCN Clinical Practice Guidelines in Oncology J Natl Compr Canc Netw 2017 15 504 535 28404761 10.6004/jnccn.2017.0050

3 Parkin DM Bray F Ferlay J Pisani P Global cancer statistics, 2002 CA Cancer J Clin 2005 55 74 108 15761078 10.3322/canjclin.55.2.74

4 Tosi D Pérez-Gracia E Atis S Vié N Combès E Gabanou M Larbouret C Jarlier M Mollevi C Torro A Del Rio M Martineau P Gongora C Rational development of synergistic combinations of chemotherapy and molecular targeted agents for colorectal cancer treatment BMC Cancer 2018 18 812 30103709 10.1186/s12885-018-4712-z PMC6090616

5 Wee P Wang Z Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways Cancers (Basel) 2017 9 10.3390/cancers9050052 PMC5447962 28513565

6 Lièvre A Bachet JB Boige V Cayre A Le Corre D Buc E Ychou M Bouché O Landi B Louvet C André T Bibeau F Diebold MD Rougier P Ducreux M Tomasic G Emile JF Penault-Llorca F Laurent-Puig P KRAS mutations as an independent prognostic factor in patients with advanced colorectal cancer treated with cetuximab J Clin Oncol 2008 26 374 379 18202412 10.1200/JCO.2007.12.5906

7 Amado RG Wolf M Peeters M Van Cutsem E Siena S Freeman DJ Juan T Sikorski R Suggs S Radinsky R Patterson SD Chang DD Wild-type KRAS is required for panitumumab efficacy in patients with metastatic colorectal cancer J Clin Oncol 2008 26 1626 1634 18316791 10.1200/JCO.2007.14.7116

8 Zhao B Wang L Qiu H Zhang M Sun L Peng P Yu Q Yuan X Mechanisms of resistance to anti-EGFR therapy in colorectal cancer Oncotarget 2017 8 3980 4000 28002810 10.18632/oncotarget.14012 PMC5354808

9 Montagut C Argilés G Ciardiello F Poulsen TT Dienstmann R Kragh M Kopetz S Lindsted T Ding C Vidal J Clausell-Tormos J Siravegna G Sánchez-Martín FJ Koefoed K Pedersen MW Grandal MM Dvorkin M Wyrwicz L Rovira A Cubillo A Salazar R Desseigne F Nadal C Albanell J Zagonel V Siena S Fumi G Rospo G Nadler P Horak ID Bardelli A Tabernero J Efficacy of Sym004 in Patients With Metastatic Colorectal Cancer With Acquired Resistance to Anti-EGFR Therapy and Molecularly Selected by Circulating Tumor DNA Analyses: A Phase 2 Randomized Clinical Trial JAMA Oncol 2018 4 e175245 29423521 10.1001/jamaoncol.2017.5245 PMC5885274

10 Bettegowda C Sausen M Leary RJ Kinde I Wang Y Agrawal N Bartlett BR Wang H Luber B Alani RM Antonarakis ES Azad NS Bardelli A Brem H Cameron JL Lee CC Fecher LA Gallia GL Gibbs P Le D Giuntoli RL Goggins M Hogarty MD Holdhoff M Hong SM Jiao Y Juhl HH Kim JJ Siravegna G Laheru DA Lauricella C Lim M Lipson EJ Marie SK Netto GJ Oliner KS Olivi A Olsson L Riggins GJ Sartore-Bianchi A Schmidt K Shih lM Oba-Shinjo SM Siena S Theodorescu D Tie J Harkins TT Veronese S Wang TL Weingart JD Wolfgang CL Wood LD Xing D Hruban RH Wu J Allen PJ Schmidt CM Choti MA Velculescu VE Kinzler KW Vogelstein B Papadopoulos N Diaz LA Jr Detection of circulating tumor DNA in early- and late-stage human malignancies Sci Transl Med 2014 6 224ra24 10.1126/scitranslmed.3007094 PMC4017867 24553385

11 Strickler JH Loree JM Ahronian LG Parikh AR Niedzwiecki D Pereira AAL McKinney M Korn WM Atreya CE Banks KC Nagy RJ Meric-Bernstam F Lanman RB Talasaz A Tsigelny IF Corcoran RB Kopetz S Genomic Landscape of Cell-Free DNA in Patients with Colorectal Cancer Cancer Discov 2018 8 164 173 29196463 10.1158/2159-8290.CD-17-1009 PMC5809260

12 Siravegna G Mussolin B Buscarino M Corti G Cassingena A Crisafulli G Ponzetti A Cremolini C Amatu A Lauricella C Lamba S Hobor S Avallone A Valtorta E Rospo G Medico E Motta V Antoniotti C Tatangelo F Bellosillo B Veronese S Budillon A Montagut C Racca P Marsoni S Falcone A Corcoran RB Di Nicolantonio F Loupakis F Siena S Sartore-Bianchi A Bardelli A Clonal evolution and resistance to EGFR blockade in the blood of colorectal cancer patients Nat Med 2015 21 827 10.1038/nm0715-827b 26151329

13 Pietrantonio F Vernieri C Siravegna G Mennitto A Berenato R Perrone F Gloghini A Tamborini E Lonardi S Morano F Picciani B Busico A Volpi CC Martinetti A Battaglin F Bossi I Pellegrinelli A Milione M Cremolini C Di Bartolomeo M Bardelli A de Braud F Heterogeneity of Acquired Resistance to Anti-EGFR Monoclonal Antibodies in Patients with Metastatic Colorectal Cancer Clin Cancer Res 2017 23 2414 2422 27780856 10.1158/1078-0432.CCR-16-1863

14 Russo M Siravegna G Blaszkowsky LS Corti G Crisafulli G Ahronian LG Mussolin B Kwak EL Buscarino M Lazzari L Valtorta E Truini M Jessop NA Robinson HE Hong TS Mino-Kenudson M Di Nicolantonio F Thabet A Sartore-Bianchi A Siena S Iafrate AJ Bardelli A Corcoran RB Tumor Heterogeneity and Lesion-Specific Response to Targeted Therapy in Colorectal Cancer Cancer Discov 2016 6 147 153 26644315 10.1158/2159-8290.CD-15-1283 PMC4744519

15 Tran B Kopetz S Tie J Gibbs P Jiang ZQ Lieu CH Agarwal A Maru DM Sieber O Desai J Impact of BRAF mutation and microsatellite instability on the pattern of metastatic spread and prognosis in metastatic colorectal cancer Cancer 2011 117 4623 4632 21456008 10.1002/cncr.26086 PMC4257471

16 Karoulia Z Gavathiotis E Poulikakos PI New perspectives for targeting RAF kinase in human cancer Nat Rev Cancer 2017 17 676 691 28984291 10.1038/nrc.2017.79 PMC6000833

17 Laurent-Puig P Cayre A Manceau G Buc E Bachet JB Lecomte T Rougier P Lievre A Landi B Boige V Ducreux M Ychou M Bibeau F Bouché O Reid J Stone S Penault-Llorca F Analysis of PTEN, BRAF, and EGFR status in determining benefit from cetuximab therapy in wild-type KRAS metastatic colon cancer J Clin Oncol 2009 27 5924 5930 19884556 10.1200/JCO.2008.21.6796

18 Loupakis F Ruzzo A Cremolini C Vincenzi B Salvatore L Santini D Masi G Stasi I Canestrari E Rulli E Floriani I Bencardino K Galluccio N Catalano V Tonini G Magnani M Fontanini G Basolo F Falcone A Graziano F KRAS codon 61, 146 and BRAF mutations predict resistance to cetuximab plus irinotecan in KRAS codon 12 and 13 wild-type metastatic colorectal cancer Br J Cancer 2009 101 715 721 19603018 10.1038/sj.bjc.6605177 PMC2736831

19 Roth AD Tejpar S Delorenzi M Yan P Fiocca R Klingbiel D Dietrich D Biesmans B Bodoky G Barone C Aranda E Nordlinger B Cisar L Labianca R Cunningham D Van Cutsem E Bosman F Prognostic role of KRAS and BRAF in stage II and III resected colon cancer: results of the translational study on the PETACC-3, EORTC 40993, SAKK 60-00 trial J Clin Oncol 2010 28 466 474 20008640 10.1200/JCO.2009.23.3452

20 Prahallad A Sun C Huang S Di Nicolantonio F Salazar R Zecchin D Beijersbergen RL Bardelli A Bernards R Unresponsiveness of colon cancer to BRAF(V600E) inhibition through feedback activation of EGFR Nature 2012 483 100 103 22281684 10.1038/nature10868

21 Corcoran RB André T Atreya CE Schellens JHM Yoshino T Bendell JC Hollebecque A McRee AJ Siena S Middleton G Muro K Gordon MS Tabernero J Yaeger R O'Dwyer PJ Humblet Y De Vos F Jung AS Brase JC Jaeger S Bettinger S Mookerjee B Rangwala F Van Cutsem E Combined BRAF, EGFR, and MEK Inhibition in Patients with BRAF V600E -Mutant Colorectal Cancer Cancer Discov 2018 8 428 443 29431699 10.1158/2159-8290.CD-17-1226 PMC5882509

22 Richman SD Southward K Chambers P Cross D Barrett J Hemmings G Taylor M Wood H Hutchins G Foster JM Oumie A Spink KG Brown SR Jones M Kerr D Handley K Gray R Seymour M Quirke P HER2 overexpression and amplification as a potential therapeutic target in colorectal cancer: analysis of 3256 patients enrolled in the QUASAR, FOCUS and PICCOLO colorectal cancer trials J Pathol 2016 238 562 570 26690310 10.1002/path.4679 PMC4785607

23 Sartore-Bianchi A Trusolino L Martino C Bencardino K Lonardi S Bergamo F Zagonel V Leone F Depetris I Martinelli E Troiani T Ciardiello F Racca P Bertotti A Siravegna G Torri V Amatu A Ghezzi S Marrapese G Palmeri L Valtorta E Cassingena A Lauricella C Vanzulli A Regge D Veronese S Comoglio PM Bardelli A Marsoni S Siena S Dual-targeted therapy with trastuzumab and lapatinib in treatment-refractory, KRAS codon 12/13 wild-type, HER2-positive metastatic colorectal cancer (HERACLES): a proof-of-concept, multicentre, open-label, phase 2 trial Lancet Oncol 2016 17 738 746 27108243 10.1016/S1470-2045(16)00150-9

24 Hainsworth JD Meric-Bernstam F Swanton C Hurwitz H Spigel DR Sweeney C Burris H Bose R Yoo B Stein A Beattie M Kurzrock R Targeted Therapy for Advanced Solid Tumors on the Basis of Molecular Profiles: Results From MyPathway, an Open-Label, Phase IIa Multiple Basket Study J Clin Oncol 2018 36 536 542 29320312 10.1200/JCO.2017.75.3780

25 Shitara K Iwata H Takahashi S Tamura K Park H Modi S Tsurutani J Kadowaki S Yamaguchi K Iwasa S Saito K Fujisaki Y Sugihara M Shahidi J Doi T Trastuzumab deruxtecan (DS-8201a) in patients with advanced HER2-positive gastric cancer: a dose-expansion, phase 1 study Lancet Oncol 2019 20 827 836 31047804 10.1016/S1470-2045(19)30088-9

26 Dimova I Popivanov G Djonov V Angiogenesis in cancer - general pathways and their therapeutic implications J BUON 2014 19 15 21 24659637

27 Battaglin F Puccini A Intini R Schirripa M Ferro A Bergamo F Lonardi S Zagonel V Lenz HJ Loupakis F The role of tumor angiogenesis as a therapeutic target in colorectal cancer Expert Rev Anticancer Ther 2018 18 251 266 29338550 10.1080/14737140.2018.1428092 PMC7493706

28 Kabbinavar FF Hambleton J Mass RD Hurwitz HI Bergsland E Sarkar S Combined analysis of efficacy: the addition of bevacizumab to fluorouracil/Leucovorin improves survival for patients with metastatic colorectal cancer J Clin Oncol 2005 23 3706 3712 15867200 10.1200/JCO.2005.00.232

29 Pineda E Salud A Vila-Navarro E Safont MJ Llorente B Aparicio J Vera R Escudero P Casado E Bosch C Bohn U Pérez-Carrión R Carmona A Ayuso JR Ripollés T Bouzas R Gironella M García-Albéniz X Feliu J Maurel J Dynamic soluble changes in sVEGFR1, HGF, and VEGF promote chemotherapy and bevacizumab resistance: A prospective translational study in the BECOX (GEMCAD 09-01) trial Tumour Biol 2017 39 1010428317705509 28621236 10.1177/1010428317705509

30 Carbone C Piro G Simionato F Ligorio F Cremolini C Loupakis F Alì G Rossini D Merz V Santoro R Zecchetto C Zanotto M Di Nicolantonio F Bardelli A Fontanini G Tortora G Melisi D Homeobox B9 Mediates Resistance to Anti-VEGF Therapy in Colorectal Cancer Patients Clin Cancer Res 2017 23 4312 4322 28298545 10.1158/1078-0432.CCR-16-3153

31 Mawalla B Yuan X Luo X Chalya PL Treatment outcome of anti-angiogenesis through VEGF-pathway in the management of gastric cancer: a systematic review of phase II and III clinical trials BMC Res Notes 2018 11 21 29329598 10.1186/s13104-018-3137-8 PMC5767044

32 De Vita F Borg C Farina G Geva R Carton I Cuku H Wei R Muro K Ramucirumab and paclitaxel in patients with gastric cancer and prior trastuzumab: subgroup analysis from RAINBOW study Future Oncol 2019 15 2723 2731 31234645 10.2217/fon-2019-0243

33 Goel G Evolution of regorafenib from bench to bedside in colorectal cancer: Is it an attractive option or merely a "me too" drug? Cancer Manag Res 2018 10 425 437 29563833 10.2147/CMAR.S88825 PMC5844550

34 Shitara K Yamanaka T Denda T Tsuji Y Shinozaki K Komatsu Y Kobayashi Y Furuse J Okuda H Asayama M Akiyoshi K Kagawa Y Kato T Oki E Ando T Hagiwara Y Ohashi Y Yoshino T REVERCE: a randomized phase II study of regorafenib followed by cetuximab vs the reverse sequence for previously treated metastatic colorectal cancer patients Ann Oncol 2019 30 259 265 30508156 10.1093/annonc/mdy526

35 Pavlakis N Sjoquist KM Martin AJ Tsobanis E Yip S Kang YK Bang YJ Alcindor T O'Callaghan CJ Burnell MJ Tebbutt NC Rha SY Lee J Cho JY Lipton LR Wong M Strickland A Kim JW Zalcberg JR Simes J Goldstein D Regorafenib for the Treatment of Advanced Gastric Cancer (INTEGRATE): A Multinational Placebo-Controlled Phase II Trial J Clin Oncol 2016 34 2728 2735 27325864 10.1200/JCO.2015.65.1901 PMC5019744

36 Boland PM Meyer JE Berger AC Cohen SJ Neuman T Cooper HS Olszanski AJ Davey M Cheng JD Lebenthal A Burtness BA Scott WJ Astsaturov IA Induction Therapy for Locally Advanced, Resectable Esophagogastric Cancer: A Phase I Trial of Vandetanib (ZD6474), Paclitaxel, Carboplatin, 5-Fluorouracil, and Radiotherapy Followed by Resection Am J Clin Oncol 2017 40 393 398 26986978 10.1097/COC.0000000000000171 PMC5026539

37 Li J Zhao X Chen L Guo H Lv F Jia K Yv K Wang F Li C Qian J Zheng C Zuo Y Safety and pharmacokinetics of novel selective vascular endothelial growth factor receptor-2 inhibitor YN968D1 in patients with advanced malignancies BMC Cancer 2010 10 529 20923544 10.1186/1471-2407-10-529 PMC2984425

38 Wang F Yuan X Jia J Bi X Zhou Z Zhou Q Li X Luo C Deng M Yi L Li Y Lu J Su W Chen H Zhu Y Wang S Apatinib Monotherapy for Chemotherapy-Refractory Metastatic Colorectal Cancer: A Multi-centre, Single-Arm, Prospective Study Sci Rep 2020 10 6058 32269247 10.1038/s41598-020-62961-5 PMC7142071

39 Xu Z Hu C Chen S Zhang C Yu J Wang X Lv H Cheng X Apatinib enhances chemosensitivity of gastric cancer to paclitaxel and 5-fluorouracil Cancer Manag Res 2019 11 4905 4915 31213909 10.2147/CMAR.S196372 PMC6549793

40 Bellesoeur A Carton E Alexandre J Goldwasser F Huillard O Axitinib in the treatment of renal cell carcinoma: design, development, and place in therapy Drug Des Devel Ther 2017 11 2801 2811 10.2147/DDDT.S109640 PMC5614734 29033542

41 Zhang Y Zou JY Wang Z Wang Y Fruquintinib: a novel antivascular endothelial growth factor receptor tyrosine kinase inhibitor for the treatment of metastatic colorectal cancer Cancer Manag Res 2019 11 7787 7803 31496821 10.2147/CMAR.S215533 PMC6701622

42 Li J Qin S Xu RH Shen L Xu J Bai Y Yang L Deng Y Chen ZD Zhong H Pan H Guo W Shu Y Yuan Y Zhou J Xu N Liu T Ma D Wu C Cheng Y Chen D Li W Sun S Yu Z Cao P Chen H Wang J Wang S Wang H Fan S Hua Y Su W Effect of Fruquintinib vs Placebo on Overall Survival in Patients With Previously Treated Metastatic Colorectal Cancer: The FRESCO Randomized Clinical Trial JAMA 2018 319 2486 2496 29946728 10.1001/jama.2018.7855 PMC6583690

43 Catenacci DVT Rasco D Lee J Rha SY Lee KW Bang YJ Bendell J Enzinger P Marina N Xiang H Deng W Powers J Wainberg ZA Phase I Escalation and Expansion Study of Bemarituzumab (FPA144) in Patients With Advanced Solid Tumors and FGFR2b-Selected Gastroesophageal Adenocarcinoma J Clin Oncol 2020 38 2418 2426 32167861 10.1200/JCO.19.01834 PMC7367551

44 Montazeri K Bellmunt J Erdafitinib for the treatment of metastatic bladder cancer Expert Rev Clin Pharmacol 2020 13 1 6 31810398 10.1080/17512433.2020.1702025

45 Curigliano G Shah RR Safety and Tolerability of Phosphatidylinositol-3-Kinase (PI3K) Inhibitors in Oncology Drug Saf 2019 42 247 262 30649751 10.1007/s40264-018-0778-4

46 Weldon Gilcrease G Stenehjem DD Wade ML Weis J McGregor K Whisenant J Boucher KM Thorne K Orgain N Garrido-Laguna I Sharma S Phase I/II study of everolimus combined with mFOLFOX-6 and bevacizumab for first-line treatment of metastatic colorectal cancer Invest New Drugs 2019 37 482 489 30302599 10.1007/s10637-018-0645-2

47 van Geel RMJM Tabernero J Elez E Bendell JC Spreafico A Schuler M Yoshino T Delord JP Yamada Y Lolkema MP Faris JE Eskens FALM Sharma S Yaeger R Lenz HJ Wainberg ZA Avsar E Chatterjee A Jaeger S Tan E Maharry K Demuth T Schellens JHM A Phase Ib Dose-Escalation Study of Encorafenib and Cetuximab with or without Alpelisib in Metastatic BRAF -Mutant Colorectal Cancer Cancer Discov 2017 7 610 619 28363909 10.1158/2159-8290.CD-16-0795 PMC5546207

48 Lorenzen S Knorrenschild JR Pauligk C Hegewisch-Becker S Seraphin J Thuss-Patience P Kopp HG Dechow T Vogel A Luley KB Pink D Stahl M Kullmann F Hebart H Siveke J Egger M Homann N Probst S Goetze TO Al-Batran SE Phase III randomized, double-blind study of paclitaxel with and without everolimus in patients with advanced gastric or esophagogastric junction carcinoma who have progressed after therapy with a fluoropyrimidine/platinum-containing regimen (RADPAC) Int J Cancer 2020 147 2493 2502 32339253 10.1002/ijc.33025

49 Fritsch C Huang A Chatenay-Rivauday C Schnell C Reddy A Liu M Kauffmann A Guthy D Erdmann D De Pover A Furet P Gao H Ferretti S Wang Y Trappe J Brachmann SM Maira SM Wilson C Boehm M Garcia-Echeverria C Chene P Wiesmann M Cozens R Lehar J Schlegel R Caravatti G Hofmann F Sellers WR Characterization of the novel and specific PI3Kα inhibitor NVP-BYL719 and development of the patient stratification strategy for clinical trials Mol Cancer Ther 2014 13 1117 1129 24608574 10.1158/1535-7163.MCT-13-0865

50 Davies BR Greenwood H Dudley P Crafter C Yu DH Zhang J Li J Gao B Ji Q Maynard J Ricketts SA Cross D Cosulich S Chresta CC Page K Yates J Lane C Watson R Luke R Ogilvie D Pass M Preclinical pharmacology of AZD5363, an inhibitor of AKT: pharmacodynamics, antitumor activity, and correlation of monotherapy activity with genetic background Mol Cancer Ther 2012 11 873 887 22294718 10.1158/1535-7163.MCT-11-0824-T

51 Gonzalez-Angulo AM Meric-Bernstam F Chawla S Falchook G Hong D Akcakanat A Chen H Naing A Fu S Wheler J Moulder S Helgason T Li S Elias I Desai N Kurzrock R Weekly nab-Rapamycin in patients with advanced nonhematologic malignancies: final results of a phase I trial Clin Cancer Res 2013 19 5474 5484 24089446 10.1158/1078-0432.CCR-12-3110 PMC3935482

52 Luo J Chen XQ Li P The Role of TGF-β and Its Receptors in Gastrointestinal Cancers Transl Oncol 2019 12 475 484 30594036 10.1016/j.tranon.2018.11.010 PMC6314240

53 Yashiro M Hirakawa K Boland CR Mutations in TGFbeta-RII and BAX mediate tumor progression in the later stages of colorectal cancer with microsatellite instability BMC Cancer 2010 10 303 20565851 10.1186/1471-2407-10-303 PMC2927997

54 Wosiak A Wodziński D Kolasa M Sałagacka-Kubiak A Balcerczak E SMAD-4 gene expression in human colorectal cancer: Comparison with some clinical and pathological parameters Pathol Res Pract 2017 213 45 49 27914767 10.1016/j.prp.2016.10.013

55 Jochems C Tritsch SR Pellom ST Su Z Soon-Shiong P Wong HC Gulley JL Schlom J Analyses of functions of an anti-PD-L1/TGFβR2 bispecific fusion protein (M7824) Oncotarget 2017 8 75217 75231 29088859 10.18632/oncotarget.20680 PMC5650414

56 Strauss J Heery CR Schlom J Madan RA Cao L Kang Z Lamping E Marté JL Donahue RN Grenga I Cordes L Christensen O Mahnke L Helwig C Gulley JL Phase I Trial of M7824 (MSB0011359C), a Bifunctional Fusion Protein Targeting PD-L1 and TGFβ, in Advanced Solid Tumors Clin Cancer Res 2018 24 1287 1295 29298798 10.1158/1078-0432.CCR-17-2653 PMC7985967

57 Katz LH Likhter M Jogunoori W Belkin M Ohshiro K Mishra L TGF-β signaling in liver and gastrointestinal cancers Cancer Lett 2016 379 166 172 27039259 10.1016/j.canlet.2016.03.033 PMC5107316

58 Konstorum A Lowengrub JS Activation of the HGF/c-Met axis in the tumor microenvironment: A multispecies model J Theor Biol 2018 439 86 99 29203124 10.1016/j.jtbi.2017.11.025 PMC5799021

59 Fuse N Kuboki Y Kuwata T Nishina T Kadowaki S Shinozaki E Machida N Yuki S Ooki A Kajiura S Kimura T Yamanaka T Shitara K Nagatsuma AK Yoshino T Ochiai A Ohtsu A Prognostic impact of HER2, EGFR, and c-MET status on overall survival of advanced gastric cancer patients Gastric Cancer 2016 19 183 191 25682441 10.1007/s10120-015-0471-6

60 Shitara K Kim TM Yokota T Goto M Satoh T Ahn JH Kim HS Assadourian S Gomez C Harnois M Hamauchi S Kudo T Doi T Bang YJ Phase I dose-escalation study of the c-Met tyrosine kinase inhibitor SAR125844 in Asian patients with advanced solid tumors, including patients with MET -amplified gastric cancer Oncotarget 2017 8 79546 79555 29108334 10.18632/oncotarget.18554 PMC5668067

61 Eisenmann DM Wnt signaling WormBook 2005 1 17 10.1895/wormbook.1.7.1 PMC4781570 18050402

62 Giannakis M Hodis E Jasmine Mu X Yamauchi M Rosenbluh J Cibulskis K Saksena G Lawrence MS Qian ZR Nishihara R Van Allen EM Hahn WC Gabriel SB Lander ES Getz G Ogino S Fuchs CS Garraway LA RNF43 is frequently mutated in colorectal and endometrial cancers Nat Genet 2014 46 1264 1266 25344691 10.1038/ng.3127 PMC4283570

63 Canesin G Evans-Axelsson S Hellsten R Krzyzanowska A Prasad CP Bjartell A Andersson T Treatment with the WNT5A-mimicking peptide Foxy-5 effectively reduces the metastatic spread of WNT5A-low prostate cancer cells in an orthotopic mouse model PLoS One 2017 12 e0184418 28886116 10.1371/journal.pone.0184418 PMC5590932

64 Amé JC Spenlehauer C de Murcia G The PARP superfamily Bioessays 2004 26 882 893 15273990 10.1002/bies.20085

65 Kubota E Williamson CT Ye R Elegbede A Peterson L Lees-Miller SP Bebb DG Low ATM protein expression and depletion of p53 correlates with olaparib sensitivity in gastric cancer cell lines Cell Cycle 2014 13 2129 2137 24841718 10.4161/cc.29212 PMC4111704

66 Bang YJ Van Cutsem E Feyereislova A Chung HC Shen L Sawaki A Lordick F Ohtsu A Omuro Y Satoh T Aprile G Kulikov E Hill J Lehle M Rüschoff J Kang YK ToGA Trial Investigators Trastuzumab in combination with chemotherapy vs chemotherapy alone for treatment of HER2-positive advanced gastric or gastro-oesophageal junction cancer (ToGA): a phase 3, open-label, randomised controlled trial Lancet 2010 376 687 697 20728210 10.1016/S0140-6736(10)61121-X

67 Shirley M Rucaparib: A Review in Ovarian Cancer Target Oncol 2019 14 237 246 30830551 10.1007/s11523-019-00629-5

68 Hallberg B Palmer RH The role of the ALK receptor in cancer biology Ann Oncol 2016 27 Suppl 3 iii4 iii15 27573755 10.1093/annonc/mdw301

69 Drilon A Siena S Ou SI Patel M Ahn MJ Lee J Bauer TM Farago AF Wheler JJ Liu SV Doebele R Giannetta L Cerea G Marrapese G Schirru M Amatu A Bencardino K Palmeri L Sartore-Bianchi A Vanzulli A Cresta S Damian S Duca M Ardini E Li G Christiansen J Kowalski K Johnson AD Patel R Luo D Chow-Maneval E Hornby Z Multani PS Shaw AT De Braud FG Safety and Antitumor Activity of the Multitargeted Pan-TRK, ROS1, and ALK Inhibitor Entrectinib: Combined Results from Two Phase I Trials (ALKA-372-001 and STARTRK-1) Cancer Discov 2017 7 400 409 28183697 10.1158/2159-8290.CD-16-1237 PMC5380583

70 Türeci O Sahin U Schulze-Bergkamen H Zvirbule Z Lordick F Koeberle D Thuss-Patience P Ettrich T Arnold D Bassermann F Al-Batran SE Wiechen K Dhaene K Maurus D Gold M Huber C Krivoshik A Arozullah A Park JW Schuler M A multicentre, phase IIa study of zolbetuximab as a single agent in patients with recurrent or refractory advanced adenocarcinoma of the stomach or lower oesophagus: the MONO study Ann Oncol 2019 30 1487 1495 31240302 10.1093/annonc/mdz199 PMC6771222

71 Yeo W Chung HC Chan SL Wang LZ Lim R Picus J Boyer M Mo FK Koh J Rha SY Hui EP Jeung HC Roh JK Yu SC To KF Tao Q Ma BB Chan AW Tong JH Erlichman C Chan AT Goh BC Epigenetic therapy using belinostat for patients with unresectable hepatocellular carcinoma: a multicenter phase I/II study with biomarker and pharmacokinetic analysis of tumors from patients in the Mayo Phase II Consortium and the Cancer Therapeutics Research Group J Clin Oncol 2012 30 3361 3367 22915658 10.1200/JCO.2011.41.2395 PMC3438233

72 Yoo C Ryu MH Na YS Ryoo BY Lee CW Kang YK Vorinostat in combination with capecitabine plus cisplatin as a first-line chemotherapy for patients with metastatic or unresectable gastric cancer: phase II study and biomarker analysis Br J Cancer 2016 114 1185 1190 27172248 10.1038/bjc.2016.125 PMC4891506

73 Takebe N Nguyen D Yang SX Targeting notch signaling pathway in cancer: clinical development advances and challenges Pharmacol Ther 2014 141 140 149 24076266 10.1016/j.pharmthera.2013.09.005 PMC3982918

74 Reinstein E Ciechanover A Narrative review: protein degradation and human diseases: the ubiquitin connection Ann Intern Med 2006 145 676 684 17088581 10.7326/0003-4819-145-9-200611070-00010

75 Taipale M Jarosz DF Lindquist S HSP90 at the hub of protein homeostasis: emerging mechanistic insights Nat Rev Mol Cell Biol 2010 11 515 528 20531426 10.1038/nrm2918

76 Skoda AM Simovic D Karin V Kardum V Vranic S Serman L The role of the Hedgehog signaling pathway in cancer: A comprehensive review Bosn J Basic Med Sci 2018 18 8 20 29274272 10.17305/bjbms.2018.2756 PMC5826678

77 Franklin C Livingstone E Roesch A Schilling B Schadendorf D Immunotherapy in melanoma: Recent advances and future directions Eur J Surg Oncol 2017 43 604 611 27769635 10.1016/j.ejso.2016.07.145

78 Hirsch FR Scagliotti GV Mulshine JL Kwon R Curran WJ Jr Wu YL Paz-Ares L Lung cancer: current therapies and new targeted treatments Lancet 2017 389 299 311 27574741 10.1016/S0140-6736(16)30958-8

79 Deschoolmeester V Baay M Lardon F Pauwels P Peeters M Immune Cells in Colorectal Cancer: Prognostic Relevance and Role of MSI Cancer Microenviron 2011 4 377 392 21618031 10.1007/s12307-011-0068-5 PMC3234325

80 Kang YK Boku N Satoh T Ryu MH Chao Y Kato K Chung HC Chen JS Muro K Kang WK Yeh KH Yoshikawa T Oh SC Bai LY Tamura T Lee KW Hamamoto Y Kim JG Chin K Oh DY Minashi K Cho JY Tsuda M Chen LT Nivolumab in patients with advanced gastric or gastro-oesophageal junction cancer refractory to, or intolerant of, at least two previous chemotherapy regimens (ONO-4538-12, ATTRACTION-2): a randomised, double-blind, placebo-controlled, phase 3 trial Lancet 2017 390 2461 2471 28993052 10.1016/S0140-6736(17)31827-5

81 Janjigian YY Bendell J Calvo E Kim JW Ascierto PA Sharma P Ott PA Peltola K Jaeger D Evans J de Braud F Chau I Harbison CT Dorange C Tschaika M Le DT CheckMate-032 Study: Efficacy and Safety of Nivolumab and Nivolumab Plus Ipilimumab in Patients With Metastatic Esophagogastric Cancer J Clin Oncol 2018 36 2836 2844 30110194 10.1200/JCO.2017.76.6212 PMC6161834

82 Panda A Mehnert JM Hirshfield KM Riedlinger G Damare S Saunders T Kane M Sokol L Stein MN Poplin E Rodriguez-Rodriguez L Silk AW Aisner J Chan N Malhotra J Frankel M Kaufman HL Ali S Ross JS White EP Bhanot G Ganesan S Immune Activation and Benefit From Avelumab in EBV-Positive Gastric Cancer J Natl Cancer Inst 2018 110 316 320 29155997 10.1093/jnci/djx213 PMC6658862

83 Fuchs CS Doi T Jang RW Muro K Satoh T Machado M Sun W Jalal SI Shah MA Metges JP Garrido M Golan T Mandala M Wainberg ZA Catenacci DV Ohtsu A Shitara K Geva R Bleeker J Ko AH Ku G Philip P Enzinger PC Bang YJ Levitan D Wang J Rosales M Dalal RP Yoon HH Safety and Efficacy of Pembrolizumab Monotherapy in Patients With Previously Treated Advanced Gastric and Gastroesophageal Junction Cancer: Phase 2 Clinical KEYNOTE-059 Trial JAMA Oncol 2018 4 e180013 29543932 10.1001/jamaoncol.2018.0013 PMC5885175

84 Shitara K Özgüroğlu M Bang YJ Di Bartolomeo M Mandalà M Ryu MH Fornaro L Olesiński T Caglevic C Chung HC Muro K Goekkurt E Mansoor W McDermott RS Shacham-Shmueli E Chen X Mayo C Kang SP Ohtsu A Fuchs CS KEYNOTE-061 investigators Pembrolizumab vs paclitaxel for previously treated, advanced gastric or gastro-oesophageal junction cancer (KEYNOTE-061): a randomised, open-label, controlled, phase 3 trial Lancet 2018 392 123 133 29880231 10.1016/S0140-6736(18)31257-1

85 Kato K Cho BC Takahashi M Okada M Lin CY Chin K Kadowaki S Ahn MJ Hamamoto Y Doki Y Yen CC Kubota Y Kim SB Hsu CH Holtved E Xynos I Kodani M Kitagawa Y Nivolumab vs chemotherapy in patients with advanced oesophageal squamous cell carcinoma refractory or intolerant to previous chemotherapy (ATTRACTION-3): a multicentre, randomised, open-label, phase 3 trial Lancet Oncol 2019 20 1506 1517 31582355 10.1016/S1470-2045(19)30626-6

86 Saeterdal I Bjørheim J Lislerud K Gjertsen MK Bukholm IK Olsen OC Nesland JM Eriksen JA Møller M Lindblom A Gaudernack G Frameshift-mutation-derived peptides as tumor-specific antigens in inherited and spontaneous colorectal cancer Proc Natl Acad Sci U S A 2001 98 13255 13260 11687624 10.1073/pnas.231326898 PMC60857

87 Overman MJ Lonardi S Wong KYM Lenz HJ Gelsomino F Aglietta M Morse MA Van Cutsem E McDermott R Hill A Sawyer MB Hendlisz A Neyns B Svrcek M Moss RA Ledeine JM Cao ZA Kamble S Kopetz S André T Durable Clinical Benefit With Nivolumab Plus Ipilimumab in DNA Mismatch Repair-Deficient/Microsatellite Instability-High Metastatic Colorectal Cancer J Clin Oncol 2018 36 773 779 29355075 10.1200/JCO.2017.76.9901

88 Jiang H Shi Z Wang P Wang C Yang L Du G Zhang H Shi B Jia J Li Q Wang H Li Z Claudin18.2-Specific Chimeric Antigen Receptor Engineered T Cells for the Treatment of Gastric Cancer J Natl Cancer Inst 2019 111 409 418 30203099 10.1093/jnci/djy134

89 Janjigian YY Vakiani E Ku GY Herrera JM Tang LH Bouvier N Viale A Socci ND Capanu M Berger M Ilson DH Phase II Trial of Sorafenib in Patients with Chemotherapy Refractory Metastatic Esophageal and Gastroesophageal (GE) Junction Cancer PLoS One 2015 10 e0134731 26275293 10.1371/journal.pone.0134731 PMC4537304

90 Hoang T Myung SK Pham TT Park B Efficacy of Crizotinib, Ceritinib, and Alectinib in ALK-Positive Non-Small Cell Lung Cancer Treatment: A Meta-Analysis of Clinical Trials Cancers (Basel) 2020 12 10.3390/cancers12030526 PMC7139871 32106398

91 Cabanillas ME Habra MA Lenvatinib: Role in thyroid cancer and other solid tumors Cancer Treat Rev 2016 42 47 55 26678514 10.1016/j.ctrv.2015.11.003

92 Broekman F Giovannetti E Peters GJ Tyrosine kinase inhibitors: Multi-targeted or single-targeted? World J Clin Oncol 2011 2 80 93 21603317 10.5306/wjco.v2.i2.80 PMC3095472

93 Jia J Zhu F Ma X Cao Z Cao ZW Li Y Li YX Chen YZ Mechanisms of drug combinations: interaction and network perspectives Nat Rev Drug Discov 2009 8 111 128 19180105 10.1038/nrd2683

94 O'Neil J Benita Y Feldman I Chenard M Roberts B Liu Y Li J Kral A Lejnine S Loboda A Arthur W Cristescu R Haines BB Winter C Zhang T Bloecher A Shumway SD An Unbiased Oncology Compound Screen to Identify Novel Combination Strategies Mol Cancer Ther 2016 15 1155 1162 26983881 10.1158/1535-7163.MCT-15-0843

95 Hu-Lieskovan S Mok S Homet Moreno B Tsoi J Robert L Goedert L Pinheiro EM Koya RC Graeber TG Comin-Anduix B Ribas A Improved antitumor activity of immunotherapy with BRAF and MEK inhibitors in BRAF(V600E) melanoma Sci Transl Med 2015 7 279ra41 10.1126/scitranslmed.aaa4691 PMC4765379 25787767

96 Wang M Liu Y Cheng Y Wei Y Wei X Immune checkpoint blockade and its combination therapy with small-molecule inhibitors for cancer treatment Biochim Biophys Acta Rev Cancer 2019 1871 199 224 30605718 10.1016/j.bbcan.2018.12.002

97 Pottier C Fresnais M Gilon M Jérusalem G Longuespée R Sounni NE Tyrosine Kinase Inhibitors in Cancer: Breakthrough and Challenges of Targeted Therapy Cancers (Basel) 2020 12 731 10.3390/cancers12030731 PMC7140093 32244867