Clumped perinuclear BAP1 expression is a frequent finding in sporadic epithelioid Spitz tumors

Background BRCA1-associated protein 1 (BAP1) represents a recently identified tumor suppressor protein. Loss of BAP1 has been observed in cutaneous epithelioid Spitz tumors. These cutaneous melanocytic tumors show a distinct histopathologic phenotype characterized by an intradermal sheet-like proliferation of epithelioid melanocytes. Methods We retrospectively reviewed the clinical outcomes, histopathologic findings and immunophenotype in spitzoid melanocytic neoplasms with the morphologic features seen in BAP1 mutated Spitz tumors. Cases were obtained from our files. BAP1 immunohistochemistry was evaluated dichotomously for the presence of nuclear staining. Results Fifteen of 19 cases showed loss of nuclear BAP1 expression. Of the 15 cases displaying nuclear loss of BAP1, clumped perinuclear staining was observed in 8 cases while 7 cases showed complete loss. Follow up ranging from 0-45 months (mean 17 months) was uneventful. Conclusions Our data are consistent with an indolent overall clinical course for epithelioid Spitz tumors with loss of BAP1. Furthermore, a large subset of epithelioid Spitz tumors display loss of nuclear expression but show a reproducible clumped perinuclear staining pattern.