Liquid Profiling of Circulating Tumor DNA in Plasma of Melanoma Patients for Companion Diagnostics and Monitoring of BRAF Inhibitor Therapy.

Background: The current standard for determining eligibility of patients with metastatic melanoma for BRAF-targeted therapy is tissue-based testing of mutations. As patients are rarely rebiopsied, detection in blood might be advantageous by enabling a comprehensive assessment of tumor mutational status in real time and thereby representing a noninvasive biomarker for monitoring BRAF therapy.

Methods: In all, 634 stage I to IV melanoma patients were enrolled at 2 centers, and 1406 plasma samples were prospectively collected. Patients were assigned to 3 separate study cohorts: study 1 for assessment of circulating tumor DNA (ctDNA) as part of companion diagnostics, study 2 for assessment of ctDNA for patients with low tumor burden and for follow-up, and study 3 for monitoring of resistance to BRAF inhibitor (BRAFi) or mitogen-activated protein kinase inhibitor therapy.

Results: Overall, a high degree of concordance between plasma and tissue testing results was observed at 90.9% (study 1) and 90.1% (study 2), respectively. Interestingly, discrepant results were in some cases associated with nonresponse to BRAFi (n = 3) or a secondary -mutant malignancy (n = 5). Importantly, ctDNA results correlated with the clinical course of disease in 95.7% and with response to treatment. Significantly, the detection of mutant ctDNA preceded relapse assessed by Response Evaluation Criteria in Solid Tumors, and was more specific than serum S100 and lactate dehydrogenase.

Conclusions: Blood-based testing compares favorably with standard-of-care tissue-based mutation testing. Importantly, blood-based testing correlates with the clinical course, even for early-stage patients, and may be used to predict response to treatment, recurrence, and resistance before radioimaging under BRAFi therapy, thereby enabling considerable improvements in patient treatment.