Molecular dissection of the RAS/RAF/MAPK pathway in primary and metastatic melanoma

Abstract

8050 Background: Given the reported presence of frequent mutation in NRAS and BRAF in many melanocytic lesions, the association of mutations activating the RAS/RAF/MAPK pathway with tumor progression in melanoma remains unclear. We compared the NRAS and BRAF mutation status with the levels of activated MAPK in paired primary and metastatic melanomas. Methods: 15 patients with material from both primary and metastatic lesions were assessed. Four patients had metastasis at initial diagnosis, the remaining patients developed metastasis from 8.5 to 66 months (mos) following initial diagnosis (median 24.1 mos). Mutations in BRAF (exons 11 and 15) and KRAS and NRAS (exons 1 and 2) were assessed by quantitative pyrosequencing. MAPK levels were assessed by immunohistochemistry on paraffin sections using phosphor-44/42 (Thr202/Tyr204) polyclonal antisera. Results: Activating NRAS point mutations were found in 3 of 15 patients, with 2 detected in the metastatic lesions; both of these had upregulation of activated MAPK compared to the primary lesions. BRAF V599 point mutations were found in 3 of 15 patients and present in both the primary and cognate metastatic lesions. All cases with BRAF or NRAS mutations had moderate to high levels of activated MAPK, as compared to only 2 of 9 patients without such mutations. The correlation of mutational status and clinical course revealed that NRAS/BRAF mutations and/or MAPK activation did not negatively impact overall survival. Conclusions: Molecular alterations in the RAS signaling pathway are associated with activated MAPK in both primary and metastatic melanoma. NRAS mutations and MAPK activation may be preferentially associated with disease progression, as opposed to BRAF mutations. However, neither NRAS/BRAF mutation nor activation of MAPK signaling pathway in primary and/or metastatic melanoma was significantly associated with poor disease outcome. Further molecular dissection using the archived material from two large melanoma neoadjuvant trials conducted in 1988 and 1994 is ongoing to determine the prognostic and predictive power of these biomarkers. No significant financial relationships to disclose.