Characterization and Clinical Utility of BRAFV600 Mutation Detection Using Cell-Free DNA in Patients with Advanced Melanoma

Abstract

Tissue-based tests for BRAFV600 mutation-positive melanoma involve invasive biopsy procedures, and can lead to an erroneous diagnosis when the tumor samples degrade. Herein, we explored a minimally invasive, cell-free deoxyribonucleic acid (cfDNA)-based platform, to retest patients for BRAFV600 mutations. This phase 2 study enrolled adult patients with unresectable/metastatic melanoma. A prescreening testing phase evaluated the concordance between a prior tissue-based BRAFV600 mutation test result and a subsequent plasma cfDNA-based test result. A treatment phase evaluated the patients who were confirmed as BRAFV600 mutation-positive, and were treated with cobimetinib plus vemurafenib. It was found that 35/54 patients (64.8%) with a mutant BRAF status by prior tissue test had a positive BRAFV600 mutation with the cfDNA test. Further, 7/118 patients (5.9%) with a wild-type BRAF status had a positive BRAFV600 mutation cfDNA test; tissue retests on archival samples confirmed BRAFV600 mutation positivity in 5/7 patients (71.4%). One of these patients received BRAF pathway-targeted therapy (cobimetinib plus vemurafenib), and had progression-free survival commensurate with previous experience. In the overall cobimetinib plus vemurafenib-treated population, 29/36 patients (80.6%) had an objective response. The median progression-free survival was 13.6 months (95% confidence interval, 9.5–16.5). Cell-free DNA–based tests may be a fast and convenient option to identify BRAF mutation status in melanoma patients, and help inform treatment decisions.