Primary alveolar rhabdomyosarcoma of bone.

Introduction: Rhabdomyosarcoma (RMS) is a malignant solid tumor of mesenchymal origin. It is the most com mon soft-tissue sarcoma in childhood and adolescence. 65% of cases are diagnosed before the age of 6. Histological subtypes include embryonal, alveolar, pleomorphic, and fused-cell RMS. The embryo nal subtype is more frequent in children, while the alveolar one is more frequent in adolescents and adults.

Objective: To describe the clinical presentation of primary alveolar rhabdomyosarcoma in a schoolgirl.

Clinical Case: 7-year-old schoolgirl with one-month history of progressive pain in her left thigh. X-ray shows a lytic lesion in the left femur diaphysis. A study was performed with 2 biopsies, immunohistochemistry, and PAX-FOXO1 studies which were compatible with alveolar RMS. Con clusion: Primary alveolar rhabdomyosarcoma of the bone is rare, but it should be considered within the differential diagnosis of primary small-round-blue cell bone tumors. Despite presenting a poor prognosis cytogenetic, this type of tumor seems to have better biological behavior, which for a successful treatment makes necessary to have a high index of suspicion in order to install a multimodal therapy in the context of a national protocol.