BAP1-inactivated melanocytic tumour with borderline histopathological features (BAP1-inactivated melanocytoma): A case report and a reappraisal.

We describe a case of BRCA1-associated protein (BAP1)-inactivated melanocytic tumour (BIMT) in a 22-year-old woman, documenting for the first time with dermoscopy its sudden development with the onset of an atypical vascular pattern within a Miescher naevus. The tumour was histopathologically atypical because of the presence of confluent pleomorphism, solid sheets of cells and grouped mitotic figures: these features were consistent with a melanocytic neoplasm with intermediate morphology ('BAP1-inactivated melanocytoma'; BIM) between a BAP1-inactivated melanocytic naevus and a BAP1-inactivated melanoma. The atypical histopathological features of the present case were different from the criteria quoted for BIM in the World Health Organization 2018 classification of skin tumours.