UV-induced multifocal cutaneous high-grade leiomyosarcoma.

Cutaneous sarcomas almost never present as multifocal disease. We describe a case of a man in his mid-90s with history of prior squamous cell carcinomas and an atypical fibroxanthoma involving the scalp who presented with multiple focal cutaneous nodules localised to the scalp, with some >3 cm. Biopsy with histopathology confirmed high-grade desmin-positive mesenchymal malignancy, with 99% of cells expressing PD-1, consistent with leiomyosarcoma (LMS). Gene expression profiling indicated a UV gene signature. The patient was treated with radiation therapy to the affected area with significant response but then developed additional cutaneous nodules inferior to the radiation field. He was subsequently treated with pembrolizumab with almost immediate resolution of the remaining nodules. This case is unique as it highlights several unusual features of cutaneous high-grade LMSs, notably presentation of multifocal disease, a UV signature and high responsiveness to anti-PD-1 therapy.