Embryonal rhabdomyosarcoma presenting in an adult: a case report and discussion of immunohistochemical staining.

Embryonal rhabdomyosarcoma is the most common soft tissue sarcoma of childhood but is rarely seen in adults. We report an embryonal rhabdomyosarcoma of the cheek in a 21-year-old Filipino man presenting as a rapidly enlarging mass. An incisional biopsy was consistent with embryonal rhabdomyosarcoma. The patient failed to respond to one cycle of chemotherapy after initial diagnosis and workup for metastatic disease. Wide local excision of the tumor was then completed with the use of the Mohs technique to clear the glabrous cutaneous margins during surgery. A Mohs surgeon and dermatopathologist were involved in interpretation of the Mohs sections. Subsequent immunohistochemical staining revealed a poorly differentiated spindled and epithelioid cell tumor, which stained diffusely positive for vimentin, S-100, and MyoD1. Rare rhabdomyoblasts were present and stained positively for desmin, muscle-specific actin, and phosphotungstic acid hematoxylin. The patient subsequently underwent radiation therapy for a total of 6,000 cGy, followed by two cycles of chemotherapy. The patient continues to be disease-free at 22 months after his wide local excision.