Melanoma NRAS/BRAF Mutations: A Population-Based Study

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DESCRIPTION (provided by applicant): Melanoma, which is rapidly increasing in incidence, remains a potentially fatal disease with poor medical treatment options and controversial methods of prevention. Because of the increasing burden of this disease and its lethality, improved methods of prevention, early diagnosis and treatment are expected to be of increasing importance. NRAS and BRAF, mediators in the RAS-RAF-MEK-ERK-MAP cell signaling pathway, are the most commonly mutated oncogenes thus far described for melanoma. However, despite the identification of these mutations in primary human melanomas, the frequency and mutational spectrum of NRAS and BRAF mutations in melanoma have not been fully characterized and there is a critical gap in the knowledge base regarding the association of these mutations with heterogeneity, precursor lesions, risk, and prognosis in melanoma. The specific aims of this study are to: (1) determine the population-based frequency and mutational spectrum of NRAS and BRAF somatic alterations in primary cutaneous invasive melanoma and their associations with histologic subtype and potential precursor lesions, and (2) determine associations between NRAS and BRAF mutational phenotypes and known prognostic indicators and risk factors. For this study, a group of approximately 300 consecutive patients with malignant melanoma in North Carolina in the year 2000 has been assembled. Complete epidemiologic data, pathology, and tumor blocks have been obtained for these patients. NRAS and BRAF somatic mutations will be detected and characterized using the highly sensitive technique of single strand conformational polymorphism (SSCP) analysis combined with direct sequencing of PCR products. The population-based frequency of these mutations will be determined and compared between pathologically distinct subtypes of melanoma (superficial spreading, lentigo maligna, nodular, and acral lentiginous). In melanoma samples associated with a nevus, this component will be analyzed separately for mutations using laser capture microdissection. Mutational phenotype will be associated with subtype, potential precursor lesions, risk factors, and prognostic indicators. The data derived from this study is expected to clarify the role of NRAS and BRAF in the development, progression and heterogeneity of melanoma, ultimately leading to better prevention, classification and treatment. Elucidation of how these mutations might arise in relationship to environmental and hereditary factors should result in more evidence-based recommendations for risk factor avoidance. In addition, understanding how mutations arise in relationship to precursors should provide information regarding which potential precursors should be removed. This study is also expected to lead to identification of new hemotherapeutic targets and more efficient testing of inhibitors for NRAS and BRAF signaling, which have recently been developed.