Noninvasive Therapeutic Monitoring of Circulating Tumor DNA in BRAF-Mutant Metastatic Colon Cancer Using Droplet Digital PCR, Next-Generation Sequencing, and Fragmentomics.

PURPOSE: BRAFV600E-mutated metastatic colorectal cancers (mCRCs) are associated with poorer prognosis. We present a case, in which noninvasive therapeutic monitoring was performed on a patient with BRAF-mutant mCRC, aiming to track disease progression and elucidate the mechanisms of response and resistance towards anti-BRAF therapy.

METHODS

A 40-year-old man diagnosed with metastatic BRAFV600E mutant sigmoid adenocarcinoma received multiple lines of treatment, including first-line chemotherapy + bevacizumab and targeted therapy of cetuximab, encorafenib ± binimetinib. Noninvasive therapeutic monitoring was performed on ctDNA using our in-house designed droplet digital PCR assay and fragmentomics. We also performed serial and paired analyses of tissue, liquid biopsy, and in vitro studies at different multiple timepoints.

RESULTS

ctDNA and fragmentomics biomarkers were concordant with, and even preceded traditional serological and radiological biomarkers in predicting disease progression. Molecular analyses and drug testing also revealed mutations that are either potentially targetable or account for resistance, which guided the subsequent treatment regimen.

CONCLUSION

This case demonstrates the potential application of ctDNA and fragmentomics biomarkers, molecular analyses, and drug testing in noninvasive therapeutic monitoring of BRAFV600E mutant mCRC. These illustrate the potential application of such noninvasive therapeutic monitoring in larger scale cohorts of patients.