LAUSR

183Background: The phase 3 COMBI-v study (NCT01597908) showed that D+T significantly improved outcomes vs vemurafenib in pts with BRAF V600E/K–mutant MM. Checkpoint inhibitors also provide clinical benefit in some pts with MM. To date, characterization of markers associated with response to anti–PD-1 therapy has identified positive associations with PD-L1 expression and immune cell infiltration. Here we describe expression of PD-L1 and the T-cell marker CD8 in tumor samples from pts randomized to receive D+T in COMBI-v and associations with clinical outcomes. Methods: Biopsies from 74 of 352 D+T pts (21%) in COMBI-v were assessed for expression of PD-L1 (PD-L1 IHC 22C3 pharmDx assay; Dako) and CD8 (anti-CD8 antibody, clone C8/144B; Dako). PD-L1 positivity was determined as a percentage of stained tumor cells and MEL score (staining on both tumor and mononuclear inflammatory cells; 0 or 1 [negative]: < 1% staining; 2-5 [positive]: ≥ 1% staining; Daud et al. J Clin Oncol. 2016). Results: Of 74 pts analyzed,...