Theragnostic significance of tumor-infiltrating lymphocytes and Ki67 in BRAFV600-mutant metastatic melanoma (BRIM-3 trial)

We conducted a retrospective tumor tissue analysis as part of the BRIM3 trial to evaluate the theragnostic significance of tumor-infiltrating lymphocytes (TILs) and melanoma cell proliferation. Using manual semi-quantitative analyses, we assessed the density of TILs by pathology review of tissue sections stained with hematoxylin and eosin (H&E TIL score) and by immunohistochemistry (IHC) with an anti–CD8 antibody (CD8 TIL score); also, the melanoma cell proliferation by IHC with an anti–Ki67 antibody. Three hundred and fifty-three, 280, and 172 patients’ tumor tissue samples were available for H&E, CD8, and Ki67 IHC analysis, respectively. There was no association between high (2+, 3+) peritumoral and intratumoral H&E and/or TIL CD8 score or high Ki67 proliferation index (>15%) with serum LDH level and stage IV melanoma. Neither high Ki67 proliferation, nor high peritumoral and/or intratumoral TIL score was significantly associated with objective antitumor response in any treatment arm. High intratumoral and high peritumoral CD8 TIL score was significantly associated with progression-free survival (PFS) only in DTIC-treated patients (P = 0.002 and 0.037, respectively); in vemurafenib-treated patients, high intratumoral and/or peritumoral CD8 TIL score was not significant (log-rank P = 0.053 and 0.062, respectively). Nevertheless, a high peritumoral CD8 TIL score was a significant predictor of PFS and overall survival after adjustment for age, sex, serum LDH, ECOG performance status, and treatment arm in a Cox regression model. Vemurafenib does not only benefit patients bearing brisk TILs; even vemurafenib-treated patients with absent and/or non–brisk TILs tend to have longer PFS compared to DTIC-treated patients with brisk TILs. High peritumoral CD8 TIL score is a favorable prognostic factor independent of well-established AJCC staging factors.