Cutaneous leiomyosarcoma in a case of hereditary leiomyomatosis and renal cell carcinoma syndrome.

Hereditary leiomyomatosis and renal cell carcinoma (HLRCC) syndrome is an autosomal-dominant disorder that results from a germline pathogenic variant in the fumarate hydratase (FH) gene on chromosome 1, characterised by renal cell carcinoma (RCC), cutaneous leiomyoma and uterine leiomyoma. Leiomyosarcomas are reported in less than 1% of those with HLRCC. We report a case of a man in his 30s who had a long-standing plaque excised from the left upper arm after undergoing a radical nephrectomy for a fumarate-deficient RCC, with histological exam revealing a grade 1 leiomyosarcoma. Genetic testing confirmed a heterozygous pathogenic variant in the FH gene. This is a rare case of leiomyosarcoma associated with HLRCC, and our patient remains under surveillance with interval abdominal imaging and skin examination. Leiomyosarcomas are difficult to distinguish clinically from their benign counterpart; therefore, histopathological examination is paramount with a low threshold for excision.