ROUTINE MELANOMA GENOTYPING PROFILE AT BARRETOS CANCER HOSPITAL

Melanoma is the 5th most common cancer in men and the 7th in women with 9,320 deaths in 2018 in the U.S. Melanoma molecular basis are well explored and it can guide the patients prognosis and therapy. In Brazil, knowledge of melanoma mutation landscape is limited. Here, we investigated the somatic variation profile of melanoma-related genes in a series of Brazilian patients. Formalin-fixed paraffin-embedded (FFPE) samples from 102 patients diagnosed with melanoma at Barretos Cancer Hospital, Brazil in 2018. Following DNA isolation, mutation analysis was done by TruSight Tumor 15 (TST15) panel at MiSeq based-next generation sequencing platform (Illumina). Panel content focuses on relevant somatic variants in 15 cancer-associated genes: AKT1, GNA11, NRAS, BRAF, GNAQ, PDGFRA, EGFR, KIT, PIK3CA, ERBB2, KRAS, RET, FOXL2, MET, and TP53. Variant calling analyses were performed using Sophia-DDM platform (Sophia). Samples were analyzed when > 500x of average coverage was observed and variants were classified when observed a minimum variant fraction of 10%. Overall, 8.8% (9/102) of cases were inconclusive due to poor quality DNA. Of the conclusive 93 cases, we observed BRAF mutations in 41.9% of cases (39/93), been the great majority (38 cases) at codon 600, and one case at codon 598. NRAS mutations were identified in 12.9% (12/93) of cases with 10 cases exhibiting mutation at codon 61, and 2 at codons 12-13. Only one case (1.1%) showed KIT mutation at exon 17. In the analyzed cases, mutations in BRAF, NRAS and KIT genes are mutually exclusive. Moreover, we identified mutations of TP53 in 9.7% (9/93) of cases, most of which are simultaneous with BRAF and NRAS variants. No variants or small percentage of variants with clinical significance were observed in EGFR, FOXL2, GNA11, GNAQ, MET, RET and AKT1, ERBB2, KRAS, PDGFRA, and PIK3CA oncogenes. Brazilian melanomas exhibit BRAF and NRAS mutation frequencies similar to the reported in the international literature. The routine identification of pathogenic and targeted mutations by TST15 panel in FFPE melanoma cases is feasible and crucial for therapeutic management of melanomas patients attended at Barretos Cancer Hospital.