Track

Case Reports

Abstract

BRCA1-associated protein 1 (BAP1)-inactivated melanocytic neoplasms are a rare subset of epithelioid melanocytic neoplasms which can occur sporadically or in association with a germline BAP1 mutation. This case series describes the histopathologic spectrum of BAP1-inactived melanocytic neoplasms, including BAP1-inactived melanocytoma (BIM), combined BIM/compound nevus, and BAP1- inactivated melanoma. Case 1 (combined BIM and compound nevus): A 32-year-old female with right chest biopsy demonstrating an atypical melanocytic proliferation with two distinct populations of melanocytes. One population was composed of poorly nested epithelioid melanocytes demonstrating loss of BAP1 and a distinct population of well-nested, banal-appearing melanocytes with retained BAP1 staining. Case 2 (BIM): A 46-year-old female with a hereditary, germline BAP-1 mutation with left dorsal wrist biopsy demonstrating a well-circumscribed melanocytic proliferation of characteristic epithelioid melanocytes with BAP-1 loss and retained p16. Case 3 (BAP1-inactivated melanoma): A 61-year-old female with right forearm biopsy demonstrating an expansile dermal proliferation of atypical epithelioid melanocytes, some with a rhabdoid-appearance, arranged in nests, sheets, and nodules with significant cytologic atypia and numerous mitotic figures. BAP1 was lost and PRAME was positive. Chromosomal microarray testing showed multiple abnormalities including BAP1 loss, gain of 6p (including RREB1), and loss of chromosome 9 (including CDKN2A)  The World Health Organization (WHO) classifies melanocytomas as genetically intermediate lesions containing at least one driver mutation, and the degree of atypia can increase with the number of mutations. The range of BAP1-inactivated melanocytic tumors can present a challenge, but careful consideration of the cytologic, architectural, immunophenotypic, and