Effects of Molecular Heterogeneity on Survival of Patients With BRAF V600 -Mutated Melanoma Treated With Vemurafenib With or Without Cobimetinib in the coBRIM Study

• Published in: JCO precision oncology Vol. 2; p. 1
• Main Authors: Wongchenko, Matthew J, Ribas, Antoni, Ascierto, Paolo A, Dréno, Brigitte, Maria di Giacomo, Anna, Garbe, Claus, Chang, Ilsung, Hsu, Jessie, Rooney, Isabelle, Lu, William, Koeppen, Hartmut, Larkin, James, Yan, Yibing, McArthur, Grant A
• Format: Journal Article
• Language: English
• Published: United States 01.11.2018
• ISSN: 2473-4284
• DOI: 10.1200/PO.17.00242

The treatment of advanced -mutated melanomas with BRAF inhibitors (BRAFi) has improved survival, but the efficacy of BRAFi varies among individuals and the development of acquired resistance to BRAFi through reactivation of mitogen-activated protein kinase (MAPK) signaling is common. We performed an exploratory, retrospective analysis to investigate the effects of allelic balance, coexisting oncogene mutations, cell proliferation signaling levels, and loss of PTEN expression on progression-free survival (PFS) in patients in the phase III coBRIM study, which compared the combination of the MEK inhibitor cobimetinib with the BRAFi vemurafenib versus vemurafenib as monotherapy. Baseline tumor samples from the intention-to-treat population were analyzed by targeted deep sequencing at a median coverage of 3,600× and by immunohistochemistry for cell proliferation markers, , and PTEN. The association of these biomarkers with PFS was assessed by Cox proportional hazards modeling. Gene expression in relation to loss of PTEN was profiled by RNA sequencing in 205 patient samples and 42 -mutated melanoma cell lines. Neither allelic balance nor coexisting mutations in the RAS/RAF/RTK pathway affected PFS in either treatment group. Increased baseline MAPK signaling and cell proliferation did not affect PFS in patients treated with cobimetinib combined with vemurafenib. PTEN loss was associated with reduced PFS in patients treated with vemurafenib alone but not in patients treated with cobimetinib combined with vemurafenib. Deeper inhibition of the MAPK pathway through targeting of both MEK and BRAF may override the effects of tumor heterogeneity and improve PFS in all patients with advanced melanoma.