TERT, BRAF, and NRAS mutational heterogeneity between paired primary and metastatic melanoma tumors

Abstract Mutational heterogeneity can contribute to therapeutic resistance in solid cancers. In melanoma, the frequency of inter- and intra-tumoral heterogeneity is controversial. We examined mutational heterogeneity within individual melanoma patients using multi-platform analysis of commonly mutated driver and non-passenger genes. We analyzed paired primary and metastatic tumors from 60 patients, and multiple metastatic tumors from 39 patients whose primary tumors were unavailable (n=271 tumors). We used a combination of multiplex SNaPshot assays, Sanger Sequencing, Mutation-specific PCR, or droplet digital PCR to determine the presence of BRAFV600, NRASQ61, and TERT-124C>T and TERT-146C>T mutations. Mutations were detected in BRAF (39%), NRAS (21%) and/or TERT (78%). Thirteen patients had TERTmutant discordant tumors; seven of these had a single tumor with both TERT-124C>T and TERT-146C>T mutations present at different allele frequencies. Two patients had both BRAF and NRAS mutations; one in different tumors and the other had a single tumor with both mutations. One patient with a BRAFmutant primary lacked mutant BRAF in least one of their metastases. Overall, we identified mutational heterogeneity in 18/99 (18%) patients. These results suggest that some primary melanomas may be comprised of subclones with differing mutational profiles. Such heterogeneity may be relevant to treatment responses and survival outcomes.