Prognostic significance of dipeptidyl peptidase-7 (DPP7) in HPV16-negative head and neck squamous cell carcinoma treated with induction chemoradiotherapy.

Introduction

Head and neck squamous cell carcinoma (HNSCC) is a type of cancer that develops in the squamous cells lining the mucous membranes of the head and neck, including the oral cavity, pharynx, and larynx. Globally, it ranks is the sixth most common cancer, with approximately 890,000 new cases and 450,000 deaths reported annually [ 1 ]. This condition can severely impair critical functions like speech, swallowing, and breathing, potentially resulting in physical deformity and a significant decline in quality of life. The 5-year survival rate for HNSCC typically ranges from 60 to 65%, depending on factors such as the cancer’s location, stage of progression, and the patient’s overall comorbidities [ 2 , 3 ].

Induction chemotherapy (IC) or chemoradiotherapy administered prior to surgery has shown potential in improving organ preservation options for patients with locally advanced HNSCC [ 4 , 5 ]. Historically, stage III/IV tumors often required complete removal of the affected organ, such as the larynx or oral cavity. However, studies indicate that initiating treatment with IC or chemoradiotherapy can achieve significant tumor shrinkage in 30–50% of cases [ 6 ]. This reduction in tumor size may enable less invasive surgical approaches, such as partial organ removal, or in cases of complete clinical response, surgery may be entirely avoided [ 7 , 8 ].

Given that early detection of HNSCC is crucial for improving survival, preserving organ function, and enabling more effective treatment [ 9 – 11 ], the identification of novel diagnostic biomarkers represents a critical research goal. This study investigates the potential of dipeptidyl peptidase 7 (DPP7) as one such biomarker for early-stage HNSCC.

Dipeptidyl peptidase 7 (DPP7), also referred to as DPP2 is an enzyme belonging to the serine peptidase family. Its main role involves hydrolyzing dipeptides from the N-terminus of polypeptides [ 12 ]. This enzyme plays a crucial role in intracellular protein catabolism, contributing to protein balance homeostasis and cellular function regulation [ 13 ].

DPP7 exists in two main forms: a soluble version located in the cytoplasm, responsible for degrading intracellular proteins, and a membrane-bound version located on the cell surface [ 14 ]. The membrane-bound form is thought to play a role in cell signaling and interactions with the extracellular environment. Both forms of DPP7 are essential for maintaining normal cellular processes and systemic physiological homeostasis [ 15 ].

DPP7 is believed to play multiple roles within cells and has been implicated in cancer development and progression [ 13 ]. While the precise mechanisms remain under investigation, DPP7 is thought to influence cell cycle regulation and apoptosis. Elevated DPP7 expression is associated with increased tumor growth and decreased cell apoptosis [ 16 ]. Additionally, DPP7 may contribute to the breakdown of the extracellular matrix, supporting tumor invasion and metastasis [ 13 ]. Its effects on cell adhesion and mobility might also be critical in promoting the spread of cancer cells [ 17 ].

Interactions between DPP7 and the immune system may affect the tumor microenvironment and potentially modulate anti-tumor immune responses. DPP7 is also thought to play a role in angiogenesis [ 18 ]. Finally, emerging evidence links DPP7 and cancer stem cells, which are crucial for tumor initiation, growth, and metastasis [ 19 ].

In this study, we evaluated the effect of Induction chemoradiotherapy on organ preservation in head and neck squamous cell carcinoma (HNSCC). Additionally, the role of DPP7 in HNSCC remains largely unexplored. Our research seeks to investigate the function of DPP7 in HNSCC and its potential as a diagnostic and prognostic biomarker. Furthermore, we aim to analyze its association with various pathological and clinical features of HNSCC.

Patients and methods

A total of 104 patients with locally advanced, non-metastatic head and neck squamous cell carcinoma (HNSCC) were enrolled in this study at the Clinical Oncology Department of Zagazig University between August 2016 and June 2024. The follow-up period lasted up to 94 months. An equal number of age- and sex-matched healthy controls were also included. The study protocol received approval from the Ethics Committee of Zagazig University (approval number: 2016-Jan-112). Before participating in the study, all patients provided written informed consent. Eligibility criteria included a confirmed diagnosis of HNSCC without any evidence of metastasis as per The American Joint Committee on Cancer Staging criteria (AJCC) [ 20 ]. Additionally, all enrolled patients were confirmed to be HPV-negative based on standardized diagnostic testing. Patients were younger than 65 years, with an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 [ 21 ], and have normal bone marrow, hepatorenal, and cardiac function. The initial assessment included a physical examination, a thorough review of the patient’s medical history, and standard laboratory tests such as regular serum chemistries and a complete blood cell count. Additional diagnostic tests may have been performed, including a chest X-ray, CT scan, or head and neck MRI. Furthermore, a triple endoscopy was conducted to assess the size of the primary lesion and its local extent.

Induction chemotherapy

The patients received induction chemotherapy consisting of the TPF regimen (docetaxel, cisplatin, and fluorouracil). Specifically, docetaxel was administered at a dose of 75 mg/m² intravenously (IV) on Day 1, cisplatin at 75 mg/m² IV on Day 1, and 5-fluorouracil (5-FU) at 1000 mg/m²/day IV as a continuous infusion over 120 h (Days 1–5). This regimen was repeated every 28 days for a total of three cycles.

Following the completion of the third cycle, the patients underwent an assessment to evaluate their response based on the latest criteria for assessing responses in solid tumors [ 22 ].

Concurrent chemotherapy and radiotherapy

Following Induction chemotherapy, patients underwent concurrent chemoradiotherapy after their treatment response had been evaluated. The treatment consisted of intravenous cisplatin 100 mg/m² IV on days 1, 22, 43 during radiation therapy.

Radiotherapy planning commences with CT simulation, where patients are immobilized in a thermoplastic mask to ensure reproducible positioning. Target volumes are meticulously delineated in a hierarchical approach: the Gross Tumor Volume (GTV) encompasses the primary tumor and any involved lymph nodes. A 5–10 mm expansion creates the Clinical Target Volume (CTV), which is subdivided into a High-Risk CTV for suspected microscopic disease and a Low-Risk CTV for elective nodal regions. Finally, a 3–5 mm margin is added to form the Planning Target Volume (PTV), accounting for setup uncertainties and organ motion.

Treatment is delivered via intensity-modulated radiation therapy (IMRT) to precisely conform doses and spare organs at risk. The prescription doses are delivered simultaneously in 35 fractions over seven weeks: 70 Gy to the primary tumor and involved nodes, 59.4–63 Gy to the High-Risk CTV, and 50–54 Gy to the elective Low-Risk CTV.

The patients were then categorized based on their response to this therapy. Those with complete responses (CR) did not require further treatment. Patients with eradicated primary tumors but remaining neck nodes underwent neck dissection. Patients showing a partial response (PR) at the primary tumor underwent conservative surgery for organ preservation if necessary. Patients whose condition progressed or did not respond to the initial treatment were shifted to an alternative treatment.

Evaluation of the levels of serum DPP7 by ELISA

Blood samples were collected by venipuncture technique from patients both before and after treatment, as well as from control subjects, and were placed into plain tubes. After allowing the samples to clot for 30 min, the tubes were centrifuged at 2000×g for 10 min at 4 °C. Finally, the sera were separated and stored at − 80 °C for further analysis. The concentration of serum DPP7 was measured using the Human Dipeptidyl Peptidase 2 (DPP7) ELISA Kit from MyBioSource, Inc., San Diego, CA, USA (Catalog # MBS9322067). The assay’s sensitivity is 0.1 ng/ml, and the detection range is 0.25 ng/ml–8 ng/ml. the cutoff is 2.869 ng/ml, which was likely selected based on the point on the ROC curve that maximizes both sensitivity (true positive rate) and specificity (true negative rate).

The tests were carried out and analyzed following the manufacturer’s instructions.

Evaluation of the DPP7 gene expression in tissues by quantitative real-time (RT-PCR)

Sample collection and Preparation

104 paired tissue specimens were obtained, consisting of head and neck squamous cell carcinoma (HNSCC) and corresponding normal tissue (located 5–6 cm from the tumor), during the local evaluation of the primary tumor by endoscopy. These specimens were frozen in liquid nitrogen at -80 °C and stored for later use. Total RNA extraction was performed on these tissues using GENEzol™ TriRNA Pure Kit, Geneaid, China according to the manufacturer’s instructions.

Complementary DNA (cDNA) synthesis

cDNA synthesis was performed using the HiScript Ⅱ 1st Strand cDNA Synthesis Kit to convert extracted RNA into complementary DNA (cDNA), serving as a PCR amplification template.

Quantitative PCR analysis

Quantitative polymerase chain reaction (qPCR) was used to evaluate the levels of DPP7 mRNA expression. The analysis utilized a CFX96 Touch Real-Time PCR Detection System and SYBR Green Chemistry. Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) mRNA levels were used as an internal control to standardize gene expression and adjust for differences in RNA input. The relative expression of DPP7 mRNA was determined using the 2 −ΔCt method.

Primer design

Primer sequences were designed for GAPDH and DPP7. The primer sequences for GAPDH were forward 5′-GGAGTCAACGGATTTGGTCGT-3′ and reverse 5′-TCTCGCTCCTGGAAGATGGT-3′. For DPP7, the primer sequences were forward 5′-GAAGCGTTCCGACAGATCAAG-3′ and reverse 5′-TCAGGTCCTTCTCGTCTGACA-3′.

Detection and interpretation of p16 expression by immunohistochemistry

The detection of p16 was performed using immunohistochemistry (IHC) with the Roche E6H4™ mouse monoclonal antibody (catalog #725–4713). Formalin-fixed, paraffin-embedded (FFPE) tissue Sects. (4–5 μm) were deparaffinized, rehydrated, and subjected to heat-induced antigen retrieval. Endogenous peroxidase activity was blocked, and the primary antibody was applied at the recommended dilution. Immunodetection was performed using a secondary antibody conjugated to horseradish peroxidase (HRP), visualized with 3,3’-Diaminobenzidine (DAB) chromogen, and counterstained with hematoxylin.

Strong and diffuse nuclear and/or cytoplasmic staining in ≥ 70% of cells was classified as positive for p16 overexpression, a finding commonly associated with high-risk HPV infection in cervical and oropharyngeal cancers.

Statistical analysis

The data were examined using the SPSS software package (v. 27, IBM, Chicago, IL, United States). The expression of DPP7 was analyzed using a student’s t-test for comparing two groups and a one-way analysis of variance (ANOVA) for comparing more than two groups. A Receiver-Operating Characteristic (ROC) curve was plotted, and the area under the ROC curve (AUC) was calculated to assess the diagnostic value of DPP7 in tissues and serum. Survival curves were generated using the Kaplan-Meier model and evaluated with log-rank tests. Variables were considered statistically significant at P < 0.05.

Results

Clinical characteristics in head and neck squamous cell carcinoma (HNSCC) patients

Most patients were male (75%), with a mean age of 48.19 years. Among the study population, 104 patients received induction chemotherapy, and 81 completed the full treatment course. The follow-up duration was 94 months. The main tumor sites were the oropharynx (43.3%) and hypopharynx (30.8%), with varying grades. Most patients had an ECOG score of 0 (79.8%). The majority of the patients were diagnosed at Stage IV (92.3%), with T4N2 (25%) and T3N2 (14.4%) being common subcategories (Table 1 ).

Table 1 Overview of clinical characteristics in head and neck squamous cell carcinoma (HNSCC) patients Number % Gender Males 78 75 Females 26 25 Age Mean (Median) 48.19 ± 11.58 (50) Range 28–66 Evaluable for response to induction chemotherapy 104 Evaluable for response to induction chemotherapy + concomitant chemoradiotherapy 88 84.6 Evaluable for response at completion of all therapy 81 77.9 Site Oral cavity Oropharynx Hypopharynx Larynx 7 45 32 20 6.7 43.3 30.8 19.2 Tumor grade Well differentiated Moderately differentiated Poorly differentiated 24 44 36 23.1 42.3 34.6 ECOG performance status 0 1 83 21 79.8 20.2 Clinical stage Stage III 8 7.7 T2N1 T3N0 T3N1 0 4 4 0 3.8 3.8 Stage IV 96 92.3 T1N2 T2N2 T3N2 T3N3 T4N0 T4N1 T4N2 T4N3 4 11 11 15 16 6 26 7 3.8 10.6 10.6 14.4 15.4 5.8 25 6.7

Response to treatment

Response to induction chemotherapy (104 patients)

Induction chemotherapy has demonstrated a high level of efficacy in treating advanced HNSCC. Among the patients treated, 16.4% achieved a complete response, while 36.5% showed a partial response. Additionally, 35.6% experienced stable disease, but unfortunately, 11.5% experienced disease progression. These results underscore the potential of induction chemotherapy in managing HNSCC (Table 2 ).

Induction Chemotherapy + Chemo-radiotherapy Response (88 patients):

Furthermore, the addition of radiotherapy to induction chemotherapy significantly improved treatment outcomes. The complete response rates increased to 59.1%, with 15.9% of patients achieving substantial partial responses. Disease stabilization was observed in 13.6% of patients, while 11.4% experienced disease progression (Table 2 ).

Table 2 Response rates and outcomes of induction chemotherapy and combined induction chemotherapy with radiotherapy in HNSCC treatment Clinical response after three cycles of induction chemotherapy (104 evaluable patients) No. % Complete response (CR) 17 16.4 Partial response (PR) 38 36.5 Stable disease (SD) 37 35.6 Progressive disease (PD) 12 11.5 Clinical response after three cycles of induction chemotherapy and concomitant chemo-radiotherapy (88 evaluable patients) CR 52 59.1 PR 14 15.9 SD 12 13.6 PD 10 11.4

Outcomes of patients with head and neck squamous cell carcinoma (HNSCC)

Our analysis of the 88 patients who completed induction chemotherapy and concomitant chemoradiotherapy revealed the following outcomes. The majority of patients (59.1%, 52/88) who achieved a complete response (CR) stopped treatment after protocol completion. Among the 14 patients with a partial response (PR), a small subset (2 patients, 2.3% of the total cohort) refused the recommended conservative surgery. Of the 12 patients with stable disease (SD), two (2.3%) were not amenable to radical surgery, and another two (2.3%) died after concomitant chemoradiotherapy. Finally, for the 10 patients with progressive disease (PD), alternative treatment strategies—defined as therapies outside the standard protocol, including palliative chemotherapy, targeted therapy, or participation in clinical trials—were employed in 8 cases (9.1% of the total cohort) (Table 3 ).

Table 3 Outcomes of treatment head and neck squamous cell carcinoma (HNSCC) Outcome of treatment No. % Stopped treatment at protocol completion because of CR 52 59.1 Refused conservative surgery (PR) 2 2.3 Not amenable to radical surgery (SD) 2 2.3 Died after concomitant chemo-radiotherapy (SD) 2 2.3 PD shifted to other treatment protocols 8 9.1 Total 66 75

DPP7 as a potential diagnostic marker in HNSCC

The evaluation of DPP7 gene expression via qRT-PCR revealed a significant increase in HNSCC tissues compared to matched nearby normal tissues (NNT). The mean relative DPP7 expression (2 −ΔCt ) was 6.6 ± 1.2 in tumor tissues versus 2.5 ± 0.3 in normal controls ( p < 0.0001), as shown in Fig. 1 A.

Additionally, the evaluation of DPP7 levels in the serum of HNSCC patients and controls revealed a significant elevation in patients (11.49 ± 2.07) compared to controls (2.3 ± 0.3) ( p < 0.0001), Fig. 1 B.

The results of the ROC curve analysis demonstrate that DPP7 expression exhibits strong discriminatory capacity between HNSCC and normal tissues, with an AUC of 1.000, a p-value < 0.0001, and a 95% confidence interval of 1.000 to 1.000, all indicating statistically significant diagnostic performance. These findings suggest that DPP7 may serve as a potential biomarker for distinguishing HNSCC from normal tissues, which could have important clinical implications (Fig. 1 C).

Similarly, the ROC curve analysis demonstrated strong discriminatory performance between HNSCC serum and control serum based on DPP7 expression, yielding an AUC of 1.000. The p-value of < 0.0001 and a 95% confidence interval of 1.000 to 1.000 indicate a statistically significant diagnostic accuracy for DPP7 in distinguishing between the two groups (Fig. 1 D).

Our findings revealed a strong association between DPP7 expression in the tissues and serum of HNSCC patients. The Pearson correlation coefficient (r) was 0.9909, and the p-value of < 0.0001 confirms a statistically significant, strong positive correlation (Fig. 1 E).

Fig. 1 Diagnostic and Prognostic performance of DPP7 as a biomarker for HNSCC

Prognostic significance of DPP7 in HNSCC: associations with patient characteristics

Table 4 summarizes the relationship between DPP7 expression in tumor tissues and patient serum with key clinicopathological features in HNSCC. DPP7 levels were significantly associated with several established prognostic factors.

Analysis of DPP7 levels in tissue samples revealed statistically significant differences across various demographic and clinical parameters (all p < 0.0001). DPP7 expression was significantly higher in older patients (> 50 years) compared to younger individuals (7.71 vs. 5.59). Statistically significant elevations were also observed in female patients compared to males (8.31 vs. 6.05) and in patients with a poor performance status (PS 1) compared to those with a good performance status (PS 0) (8.4 vs. 6.16). However, these latter findings regarding sex and performance status should be interpreted with caution, as the female ( n = 26) and PS 1 ( n = 21) subgroups were relatively small, and the analysis may be underpowered for these variables. Furthermore, DPP7 expression increased with worsening tumor differentiation, rising from 5.07 in well-differentiated tumors to 8.07 in poorly-differentiated tumors. Patients with advanced stage IV disease exhibited higher DPP7 levels compared to those with stage III disease (6.77 vs. 4.7).

Identical trends were observed in serum DPP7 levels, with all comparisons reaching statistical significance ( p < 0.0001). This consistency between tissue and serum samples indicates that DPP7 may serve as a reliable circulating biomarker for the non-invasive monitoring of disease status.

Table 4 Relationship between DPP7 expression and clinicopathological factors in HNSCC Tissues Serum No % Mean SD P Mean SD P Age ≤ 50 years 54 51.9 5.59 0.55 17.05* < 0.0001 9.79 1.19 16.56* < 0.0001 > 50 years 50 48.1 7.71 0.72 13.32 0.96 Sex Males 78 75 6.05 0.85 13.16* < 0.0001 10.61 1.6 11.01* < 0.0001 Females 26 25 8.31 0.33 14.12 0.42 Performance Status 0 83 79.8 6.16 0.94 10.74* < 0.0001 10.79 1.71 9.14* < 0.0001 1 21 20.2 8.4 0.3 14.24 0.369 Grade Well differentiated 24 23.1 5.07 0.32 363.8** < 0.0001 8.64 0.57 386.1** < 0.0001 Moderate differentiated 44 42.3 6.26 0.45 11.15 0.82 Poorly differentiated 36 34.6 8.07 0.49 13.8 0.65 Clinical Stage Stage III 8 7.7 4.7 0.07 5.053* < 0.0001 8.05 0.1 5.545* < 0.0001 Stage IV 96 92.3 6.77 1.15 11.77 1.9 *Student t test, **One way ANOVA

Evaluation of DPP7 expression as a biomarker for treatment response in HNSCC

DPP7 expression was analyzed in relation to treatment response in HNSCC patients (Fig. 2 ). In tumor tissues, a significant stepwise increase in DPP7 levels was observed with worsening clinical outcome, from lowest in patients with a complete response (CR) to highest in those with progressive disease (PD) ( p < 0.0001, Fig. 2 A). A highly similar pattern was found in serum samples, where DPP7 concentrations also increased progressively across response categories (CR to PD, p < 0.0001, Fig. 2 B).

Together, these findings suggest an association between elevated DPP7 expression and poorer treatment response and prognosis. Furthermore, the consistent pattern observed in serum indicates that circulating DPP7 could serve as a non-invasive biomarker for predicting therapeutic efficacy and monitoring disease outcome in HNSCC.

Fig. 2 DPP7 Expression in HNSCC Tissues (A) and Serum (B) Stratified by Clinical Response to Treatment (CR: Complete Response, PR: Partial Response, SD: Stable Disease, PD: Progressive Disease)

Univariate and multivariate analysis of DPP7 as a prognostic biomarker in HNSCC

Univariate analysis revealed significant correlations between DPP7 expression in tumor tissues and key prognostic factors in HNSCC (Table 5 ). DPP7 levels increased significantly with patient age ( p < 0.0001) and were higher in females than in males ( p < 0.0001). Furthermore, DPP7 expression demonstrated a strong positive association with advancing disease stage (Stage IV vs. Stage III, p < 0.0001) and showed progressively higher levels with worsening tumor grade ( p < 0.0001). These findings support the role of DPP7 as a valuable prognostic biomarker for risk stratification in HNSCC.

Table 5 Univariate analysis of DPP7 expression correlation with prognostic factors in head and neck squamous cell carcinoma (HNSCC) Variable Estimate Standard Error 95% Confidence Interval t-statistic P -value Age Intercept 3.469 0.195 3.083 to 3.855 17.82 < 0.0001 Age Coefficient 2.124 0.125 1.877 to 2.371 17.05 < 0.0001 Sex Intercept 6.045 0.096 5.855 to 6.235 63.03 < 0.0001 Sex Coefficient (Female vs. Male) 2.255 0.156 1.945 to 2.564 14.46 < 0.0001 Tumor Grade Intercept 5.07 0.065 4.941 to 5.199 78.05 < 0.0001 Grade Coefficient 1.526 0.06 1.407 to 1.646 25.35 < 0.0001 Clinical Stage Intercept 4.7 0.281 4.142 to 5.258 16.71 < 0.0001 Stage Coefficient (IV vs. III) 2.071 0.41 1.258 to 2.884 5.05 < 0.0001

The multivariate analysis confirms that DPP7 is an independent prognostic marker in head and neck squamous cell carcinoma (HNSCC) (Table 6 ). Even after adjusting for other factors, DPP7 shows strong associations with important disease characteristics. Specifically, DPP7 levels increase with age ( p < 0.0001), women have higher DPP7 levels than men ( p < 0.0001), DPP7 levels rise with tumor undifferentiation ( p < 0.0001), and patients with advanced Stage IV disease have higher DPP7 levels than those in Stage III ( p < 0.0001). These findings establish DPP7 as a significant independent prognostic biomarker in HNSCC, and its strong connections to adverse clinicopathological features underscore its potential to improve risk stratification and inform personalized treatment strategies.

Table 6 Multivariate analysis of DPP7 as an independent prognostic marker in head and neck squamous cell carcinoma Variable Estimate Standard error 95% confidence interval |t| P value Intercept 1.859 0.2128 1.437 to 2.282 8.736 < 0.0001 B: Age 0.7732 0.08688 0.6008 to 0.9456 8.9 < 0.0001 C: Sex 0.7825 0.09171 0.6005 to 0.9645 8.532 < 0.0001 D: Pathological differentiation 0.6947 0.07067 0.5545 to 0.8349 9.831 < 0.0001 E: Stage 0.5923 0.1148 0.3644 to 0.8202 5.157 < 0.0001

DPP7 expression and survival in HNSCC patients

The overall and disease-free survival analyses provide compelling evidence that HNSCC prognosis is powerfully dictated by DPP7 expression status. Both the log-rank and Gehan-Breslow-Wilcoxon tests demonstrate the survival curves are highly statistically distinct between high and low DPP7 groups ( p < 0.005 for both) (Fig. 3 ).

The survival disparities are staggering. Median overall survival was just 23.74 months for patients with high tumor DPP7, compared to an impressive 67.82 months in the low DPP7 cohort (Fig. 3 A). Similarly, the median disease-free survival was 23.74 months in the high DPP7 group versus 66.03 months for low DPP7 - an over 2.7-fold difference ( p < 0.001 for both) (Fig. 3 B).

Fig. 3 Survival in HNSCC patients according to DPP7 Expression

Discussion

Head and neck squamous cell carcinoma (HNSCC) represents a major clinical challenge, significantly impairing vital functions and quality of life [ 23 ]. Our study reinforces the value of induction chemotherapy followed by concurrent chemoradiotherapy as an organ-preservation strategy, aligning with the paradigm shift towards mitigating long-term treatment effects [ 6 ]. This sequential approach achieved an overall response rate of 74%, and notably, enabled 59.1% of complete responders to avoid radical surgery. Despite this overall efficacy, treatment responses were heterogeneous, and a subset of patients experienced disease progression or suboptimal outcomes.

Treatment decisions were nuanced, influenced by patient preference and medical contraindications, such as comorbidities and frailty. It is noteworthy that approximately 60% of patients who achieved complete responses were able to avoid radical or disfiguring surgical procedures, thereby preserving their quality of life. Additionally, some patients opted against conservative surgery despite achieving partial responses, while others were deemed ineligible for radical surgery due to stable disease, where the tumor neither regressed sufficiently to qualify as a partial response nor progressed.

The results of our study regarding the effectiveness of induction chemotherapy in HNSCC are consistent with previous research. The overall response rate of 74% after concurrent chemoradiotherapy aligns with the findings reported in the literature [ 23 ]. Similarly, the 16% complete response rate observed in our study is comparable to outcomes from a meta-analysis of related trials [ 24 ]. Variations in response rates across studies may be attributed to differences in patient demographics, treatment protocols, and criteria used to evaluate outcomes.

Our findings indicate that the treatment strategy implemented in this study is associated with encouraging survival outcomes. These results align with prior research on the use of induction chemotherapy followed by concurrent chemoradiotherapy in this patient group. For context, one study involving advanced HNSCC patients reported a median overall survival of 14 months and a median progression-free survival of 8 months, while other studies showed a median overall survival of 18 months and a median progression-free survival of 12 months in patients with locally advanced HNSCC treated with this approach [ 25 ]. The survival outcomes in our study appear more favorable than these historical reports, potentially due to differences in patient characteristics, treatment protocols, or follow-up durations. The response rates observed in our study are consistent with earlier findings, reinforcing the established effectiveness of induction chemotherapy combined with concurrent chemoradiotherapy for head and neck cancer patients. It is essential to acknowledge that the findings of our study are constrained by a small sample size and a relatively short follow-up period. Further research is required to evaluate the long-term effectiveness and safety of using induction chemotherapy in combination with concurrent chemoradiotherapy for the treatment of head and neck squamous cell carcinoma (HNSCC).

To investigate potential biomarkers for predicting treatment response in HNSCC, we evaluated the role of DPP7. DPP7 expression was found to be significantly elevated in both tissue and serum samples from HNSCC patients compared to normal controls ( p < 0.0001). ROC curve analysis indicated a high degree of discriminatory power (AUC = 1.000) between HNSCC and normal samples in this cohort, suggesting its potential utility as a sensitive and specific diagnostic biomarker. This observed upregulation of DPP7 is consistent with reports in other malignancies, including colorectal cancer and multiple myeloma [ 17 , 18 , 26 , 27 ] .

Our analysis revealed a clear association between elevated DPP7 levels and unfavorable treatment outcomes, where patients with progressive disease exhibited the highest expression in both tissue and serum. This gradient of increasing DPP7 with worsening response suggests that DPP7 is not merely a passive marker but may be functionally implicated in mechanisms of therapeutic resistance, such as enhanced cell survival or altered drug metabolism. The strong concordance of this pattern in serum is particularly significant, as it indicates that circulating DPP7 could serve as a practical, non-invasive biomarker. This could allow for the pre-treatment identification of patients at high risk of treatment failure, enabling more personalized, risk-adapted therapeutic strategies, and facilitate post-treatment monitoring for early signs of recurrence.

We next assessed the relationship between DPP7 levels and clinicopathological characteristics. DPP7 expression in tumor tissue was significantly associated with several adverse prognostic factors, including older age, female sex, poor performance status, advanced tumor stage, and higher grade (all p < 0.0001). An identical pattern of associations was observed for serum DPP7 levels, reinforcing its potential as a practical, circulating biomarker. In both univariate and multivariate analyses, DPP7 was confirmed as a strong independent prognostic factor for survival. This link between elevated DPP7, aggressive disease features, and poorer outcomes is consistent with its reported role in other malignancies such as colorectal cancer and multiple myeloma [ 16 – 18 , 26 , 27 ].

The correlation in our cohort between high DPP7 expression, advanced disease stage, and poor tumor grade aligns with reports in colorectal cancer, where DPP7 is also linked to advanced stage and lymphatic invasion [ 18 , 26 ]. Furthermore, the identification of DPP7 as an independent prognostic factor in HNSCC is consistent with its role as a marker of aggressive disease in other malignancies, including multiple myeloma [ 16 , 27 ].

In our cohort, elevated DPP7 expression was associated with a poorer prognosis, as patients with high DPP7 levels had significantly shorter overall and disease-free survival than those with low levels. This association between high DPP7 and inferior survival is consistent with its role as a negative prognostic factor in other malignancies, including colorectal cancer [ 17 ], multiple myeloma [ 27 ], and breast cancer [ 13 ].

This study has several limitations that should be considered when interpreting the findings. First, its single-center, retrospective design and modest sample size ( n = 104) may limit the generalizability of the results and reduce statistical power for subgroup analyses, such as those involving female patients or individuals with a poor performance status. The retrospective nature also introduces the potential for selection bias.

The observed perfect diagnostic discrimination of DPP7 (AUC = 1.000) should be interpreted in the context of the study design. While this indicates a strong differential expression between patients and healthy controls in our cohort, such a high AUC can sometimes result from the case-control study design itself, which compares a well-defined diseased group to healthy individuals. This performance needs to be assessed in future studies that include patients with other head and neck pathologies to confirm its diagnostic utility in a more clinically representative setting.

Furthermore, the lack of an external validation cohort is a significant constraint for confirming the prognostic value of DPP7 in independent populations. Beyond its correlative role, the study did not explore the underlying molecular mechanisms of DPP7 in HNSCC pathogenesis. Additionally, potential confounding factors, such as detailed data on smoking, alcohol use, and comorbidities, were not fully accounted for and could influence both DPP7 expression and clinical outcomes. Finally, while the follow-up duration was substantial, it may not be sufficient for evaluating very late recurrences or secondary malignancies.

Future studies should involve larger, multi-center, prospective cohorts to validate these findings. Furthermore, functional analyses are required to elucidate the biological mechanisms through which DPP7 contributes to HNSCC pathogenesis.

Conclusion

In conclusion, our study indicates that induction chemotherapy followed by concurrent chemoradiotherapy can be an effective organ-preservation approach for locally advanced HNSCC. Furthermore, our data associate DPP7 with clinically important characteristics in this cancer. Elevated DPP7 expression in both tumor tissue and serum was correlated with adverse clinicopathological features and could serve as a potential independent prognostic factor in our cohort. The observed stepwise increase in DPP7 levels with worsening treatment response suggests a possible involvement in therapeutic resistance. The consistency of these findings in serum samples indicates that circulating DPP7 warrants further evaluation as a potential non-invasive biomarker. These results support future studies to validate the utility of DPP7 for risk stratification and to investigate its biological function in HNSCC.

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Change history

11/16/2025

This article has been updated to correct the acknowledgement.

Acknowledgements

The authors extend their appreciation to Taif University, Saudi Arabia, for supporting this work through project number (TU-DSPP-2024-54).

Author contributions

Final Approval: All authors.

Funding

This research was funded by Taif University, Saudi Arabia, project No. (TU-DSPP-2024-54).

Data availability

Data is provided within the manuscriptAny additional Data will be available upon request.

Declarations

Ethics approval and consent to participate

The authors are accountable for all aspects of the work in ensuring that accuracy and integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Helsinki Declaration (revised in 2013). The study was approved by the Research Ethics Committee of Faculty of Medicine, Zagazig University (No. 112: 2016-Jan). Informed consent was obtained from all participants.

Consent for publication

All authors confirm they have read and approved the final manuscript. The work has not been published previously, is not under consideration elsewhere, and contains no previously published material by any author. All authors agree to submission to Discover Oncology.

Competing interests

The authors declare no competing interests.

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