BAP1-Inactivated Melanocytic Tumors With Distinctive p16-Negative Clonal Growth and Liver Metastases

BAP1-inactivated melanocytic tumor (BIMT) represents a distinct subtype of melanocytoma, with characteristic morphologic features. These lesions are associated with inactivation of the BAP1 tumor suppressor gene. Although there are frequently histologic features that might otherwise cause concern for malignancy, including enlarged cells with nuclear variability, prominent nucleoli, and a lymphocytic inflammatory infiltrate, empirical data suggest that the majority behave in a clinically benign fashion. We report 2 cases of cutaneous BIMT with a distinctive morphologic pattern of clonal expansion with p16 loss. In both cases, there was liver metastasis after complete excision, in the absence of locoregional recurrence. These rare cases highlight the possibility of a distinct pathway of malignant progression in BIMT.