Concordance of somatic mutation profiles (BRAF, NRAS, and TERT) and tumoral PD-L1 in matched primary cutaneous and metastatic melanoma samples

Despite the efficacy of BRAF-targeted and PD-L1–related immune therapies in tackling metastatic melanoma, a significant number of patients exhibit resistance. Given this, the objective of the current study was to ascertain concordance of somatic mutations in BRAF/NRAS/TERT and immunohistochemical PD-L1 and CD8 in matched primary cutaneous and metastatic melanoma. A total of 43 archival paired samples with sufficient material for genetic and immunohistochemical analyses met the criteria for inclusion in the study. Immunohistochemistry was performed for PD-L1 and CD8 and direct-DNA Sanger sequencing for BRAF/NRAS/TERT promoter mutational analyses. Agreement between paired samples was assessed using Cohen κ. Poor concordance among primary and corresponding metastases was noted in BRAF (9/42 cases discordant, κ = 0.49; 95% confidence interval [CI], 0.21-0.77; P =.0013), TERT promoter mutations (13/41 cases discordant, κ = 0.33; 95% CI, 0.04-0.62; P =.033), tumoral PD-L1 immunoexpression (9/43 cases discordant, κ = 0.39; 95% CI, 0.07-0.72; P =.0099), and immunoexpression of CD8⁺ T lymphocytes (12/43 cases discordant, κ = 0.44; 95% CI, 0.19-0.69; P =.002). Although NRAS1 and NRAS2 were highly concordant (42/43 and 39/43 cases, respectively), discordant NRAS2 mutational status was associated with a median time to metastasis of 90 versus 455 days for pairs with concordant status (P =.07). Although limited by sample size, our findings suggest that consideration be given to mutational analysis of metastatic tissue rather than the primary to guide BRAF-targeted therapy and question the roles of TERT promoter mutations and PD-L1 as predictive biomarkers in malignant melanoma.