Prognostic Role of BRAFV600E Cellular Localization in Melanoma

BACKGROUND: Approximately half of cutaneous melanoma tissues harbor BRAF(V600E) mutations, resulting in a constitutive activation of the mitogen-activated protein kinase (MAPK) pathway. Nuclear-cytoplasmic transport machinery is dysregulated in neoplastic cells and alters the key regulatory proteins that can lead to tumor progression and drug resistance. The significance of nuclear localization of BRAF(V600E) has not been fully understood. We examined the clinical significance of intracellular localization of BRAF(V600E) in cutaneous melanoma. STUDY DESIGN: Immunohistochemical analysis of BRAF(V600E) was performed on formalin-fixed, paraffin-embedded specimens of cutaneous melanoma (n = 91). Staining intensity was graded in a blinded manner. Correlations to clinical factors were analyzed by Fisher's exact test and 2-tailed t-test. Localization of BRAF(V600E) was determined in melanoma cells, and we investigated their resistance to BRAF(V600E)specific inhibitor according to nuclear localization in both in vitro and in vivo models. RESULTS: We included 91 patients, of whom32% (29 of 91) had cytoplasmic BRAF(V600E). Nuclear BRAF(V600E) was observed in 30% (27 of 91). Overall, BRAF(V600E) expression correlated with TNM stage (p = 0.011), mitotic activity (p = 0.010), and ulceration (p = 0.045). Nuclear BRAF(V600E) expression correlated with overall clinical stage (p < 0.001), tumor size (p < 0.001), regional lymph node (p < 0.017), depth of invasion (p = 0.005), Clark level (p < 0.001), mitotic activity (p < 0.001), ulceration (p < 0.001), and margin status (p = 0.017). On a cellular level, BRAF(V600E) was identified in the nucleus, and its translocation was serum dependent. Our in vitro and in vivo data revealed sequestration of BRAF(V600E) in the cytosol-sensitized resistant cells to vemurafenib; nuclear retention of BRAF(V600E) was associated with aggressiveness and drug resistance. CONCLUSIONS: Nuclear localization of BRAF(V600E) is associated with melanoma aggressiveness. Further multi-institutional studies are warranted to confirm the clinical relevance of nuclear localization of BRAF(V600E). (C) 2018 by the American College of Surgeons. Published by Elsevier Inc. All rights reserved.