Vulvar and vaginal melanoma: A unique subclass of mucosal melanoma based on a comprehensive molecular analysis of 51 cases compared with 2253 cases of nongynecologic melanoma

Abstract

BACKGROUND Optimal treatments for vulvar and vaginal melanomas (VVMs) have not been identified. Herein, the authors compare molecular profiles between VVM and nongynecologic melanoma (NGM) subtypes with the objective of identifying novel, targetable biomarkers. METHODS In total, 2304 samples of malignant melanoma that were submitted to Caris Life Sciences between 2009 and 2015 were reviewed. In situ hybridization and immunohistochemistry were used to assess copy numbers and protein expression of selected genes. Sequenced variants were analyzed using a proprietary cancer panel. RESULTS In total, 51 VVMs (14 vaginal and 37 vulvar melanomas) were compared with 2253 malignant NGMs, including 2127 cutaneous, 105 mucosal, and 21 acral melanomas. In VVMs, B‐Raf proto‐oncogene serine/threonine kinase (BRAF) was the most frequently mutated gene (26%) compared with 8.3% of mucosal NGMs (P = .008). In BRAF‐mutated tumors, fewer VVMs (50%), compared with NGMs (82.1%), had a variant within the valine codon 600 (V600) domain. The KIT mutation rate was highest in VVMs (22%) compared with 3% in cutaneous (P < .001) and 8.8% in mucosal (P = .05) melanoma subtypes. NRAS mutations were rare in VVMs compared with cutaneous (25.9%; P = .009) and acral (40.6%; P = .002) melanoma subtypes. PD‐L1 (56%) and PD‐1 (75%) were frequently expressed in VVM, whereas PI3KCA pathway mutations and estrogen receptor/progesterone receptor expression were rare. Compared with VVMs that had KIT mutations, wild‐type KIT VVMs were more likely to express molecular markers suggestive of platinum resistance (ERCC1), alkylating sensitivity (MGMT), and anthracycline sensitivity (TOP2A). CONCLUSIONS The unique molecular features of VVM render this disease a distinct subtype of melanoma. Gene‐based molecular therapy and immunotherapies may be promising and should be evaluated in clinical trials. Cancer 2017;123:1333–1344. © 2016 American Cancer Society.