Histiocyte-rich rhabdomyoblastic tumor easily misdiagnosed as rhabdomyosarcoma: a case report

Histiocyte-rich rhabdomyoblastic tumor (HRRMT) is an extremely rare tumor of uncertain origin. Morphologically, it closely resembles inflammatory leiomyosarcoma (ILMS) without smooth muscle differentiation, making clinical diagnosis particularly challenging. Due to its rarity, HRRMT is often misdiagnosed as rhabdomyosarcoma, leading to unnecessary aggressive treatment.

A 62-year-old male was admitted to the hospital after an incidental discovery of a mass on his right thigh, first noticed seven days prior. Clinical examination revealed a well-circumscribed, painless mass measuring approximately 5 × 6 cm. Ultrasound and magnetic resonance imaging (MRI) suggested rhabdomyosarcoma in the distal sartorius muscle. However, histopathological analysis following surgical resection confirmed HRRMT. The patient did not undergo postoperative radiotherapy or chemotherapy, and no recurrence was observed during six months of follow-up.

HRRMT is a rare tumor with favorable biological behavior. Given its morphological overlap with ILMS and rhabdomyosarcoma, early and accurate diagnosis is essential to prevent overtreatment. Extensive surgical resection remains an effective therapeutic approach. We report a case of HRRMT that is easily misdiagnosed as rhabdomyosarcoma, which will be a valuable case.