Mutation frequency in BRAF and NRAS genes among primary tumors and different types of metastasis from melanoma patients.

8574 Background: Mutations of NRAS and BRAF genes have been identified with high frequency in nevi, cutaneous melanomas, and melanoma metastases. Prevalence of such mutations during the disease progression phases and among the different types of metastasis still remains inconclusive. Methods: Paired samples of microdissected invasive primary melanomas (N=73) and synchronous or asynchronous metastases (N=164) from same patients underwent mutation analysis by automated DNA sequencing. Secondary lesions were from: regional (RN; N=49) or distant (DN; N=16) lymph nodes; regional (RS; N=16) or distant (DS; N=18) skin; visceral (VM; N=22) and brain (BM; N= 44) sites. Results: To date, mutations were identified in 44/73 (60%) primary melanomas [42% BRAF - 18% NRAS], 43/65 (66%) lymph nodes [49% BRAF - 17% NRAS], 21/34 (62%) subcutaneous metastases [38% BRAF - 24% NRAS], 13/22 (59%) visceral metastases [45% BRAF - 14% NRAS], and 31/44 (70%) brain metastases [48% BRAF - 23% NRAS]. Overall, a slight and not significant increase in mutation frequency after progression from primary melanoma was observed in our series: 108/164 (66%) mutated metastases [46% BRAF - 20% NRAS]. The only significant differences were found for subcutaneous metastases: a) DS presented a significantly higher mutation frequency than RS (78% vs. 44%); and b) a discontinuous pattern of BRAF/NRAS mutations was detected in primary melanomas vs. RS and DS lesions. These latter findings suggest that independent subclones may have been generated. Conclusions: Although collection and analysis of samples is still ongoing, our results may provide further clues about the impact of NRAS and BRAF mutations among the different stages of melanoma progression.