Sclerosing spindle cell rhabdomyosarcoma in an adult: report of a new case and review of the literature.

Sclerosing spindle cell rhabdomyosarcoma (SSRMS) is a newly recognized entity in adults. The authors report a new case of SSRMS in a 31-year-old woman who presented with a large right leg mass. Biopsy revealed a malignant spindle cell neoplasm with focal sclerotic areas. A diagnosis of monophasic synovial sarcoma was favored initially. The tumor cells in the resection specimen were positive for myosin, myogenin, and MyoD1. Fluorescence in situ hybridization performed on the resection specimen showed no evidence of SYT gene rearrangement in the neoplastic cells, ruling out monophasic synovial sarcoma. A diagnosis of SSRMS was established. The patient succumbed to widely metastatic disease 16 months after initial diagnosis. This case highlights the utility of skeletal muscle markers and cytogenetic testing in distinguishing SSRMS from its mimic, monophasic synovial sarcoma. It is hoped that this case will expand the literature on adult SSRMS and help clinicians and pathologists better understand this newly described entity.