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.