Clear-cell variant of superficial cutaneous leiomyosarcoma associated with RB1 mutation: Clinical, dermoscopic, and histopathological characteristics.

Leiomyosarcoma is a relatively rare soft tissue tumor whose clear-cell variant has only been reported in leiomyosarcomas of the uterus. We report here for the first time a primary cutaneous clear-cell leiomyosarcoma in the trunk skin of a 49-year-old man, characterized by a very indolent clinical and dermoscopic presentation, mimicking a dermatofibroma. Genetic analysis of the otherwise healthy patient revealed a germline mutation in the retinoblastoma 1 gene (RB1); the same mutation was found in his son, who had previously developed retinoblastoma. Moreover, the mother of the patient had died of uterine leiomyosarcoma with clear-cell changes. Mutations in the RB1 gene occur commonly in human neoplasms. In this patient, we were able to link his clear-cell variant of cutaneous leiomyosarcoma with the loss of retinoblastoma protein expression, as revealed by immunohistochemical staining analysis.

Cutaneous Malignant Peripheral Nerve Sheath Tumor.

Cutaneous malignant peripheral nerve sheath tumors (MPNSTs) are rare sarcomas of neuroectodermal origin arising in the dermis and/or subcutis. In contrast with their deep soft tissue and visceral counterparts, cutaneous MPNSTs are rarely associated with neurofibromatosis type 1. Two main subtypes of cutaneous MPNST can be distinguished histologically: conventional (ie, spindle cell) and epithelioid MPNST. The 2 subtypes also differ in predilection for deep versus superficial locations, association with preexistent benign peripheral nerve sheath tumors and S100 immunohistochemistry. Herein, we review current knowledge of cutaneous MPNST and discuss its differential diagnosis.