PD-L1 and CD8 expression and association with outcomes in patients (pts) with BRAF V600E/K-mutant metastatic melanoma (MM) who received dabrafenib + trametinib (D+T) in the randomized phase 3 COMBI-v study.

Abstract

9527 Background: The phase 3 COMBI-v study (NCT01597908) showed that D+T significantly improved outcomes vs vemurafenib in pts with BRAFV600E/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, 54 (73%) had PD-L1–positive tumors, and the largest MEL score subgroup was 2 (45%). A significant association ( P < .0001) was observed between PD-L1 and CD8 expression. Overall response rate, tumor shrinkage, progression-free survival, overall survival (OS), and duration of response with D+T were not associated with PD-L1 (MEL score of ≥ 2) or CD8 positivity. However, a significant association ( P = .04) with improved OS was observed in tumors with high PD-L1 expression (≥ 20% of cells PD-L1 positive), and a trend ( P = .06) was seen in pts with a MEL score of ≥ 3. Among PD-L1–negative pts, improved OS was seen in those with high CD8 positivity ( P = .03), particularly in the stromal compartment. Conclusions: These data, representing PD-L1 and CD8 expression profiles for a BRAF-mutant mm population in the context of outcomes following D+T, showed that clinical benefit was maintained regardless of immune phenotype. The results also suggest that an immune component has an impact on outcomes following targeted therapy. Clinical trial information: NCT01597908.