Rhabdomyosarcoma (RMS) is an aggressive soft tissue sarcoma derived from embryonic mesenchymal tissue, specifically striated muscle. These tumors can arise from multiple locations, including the head and neck, extremities, and the genitourinary tract. It is one of the “small round blue cell tumors” of childhood (Ewing’s sarcoma, Carcinoid, Medulloblastoma, Neuroblastoma, and Wilms’ tumor comprise the others) that microscopically resemble fetal skeletal muscle cells. Spindle cells are also often present.
Three histological subtypes are recognized by the Intergroup RMS Study Group (IRSG)/Children’s Oncology Group (COG): Embryonal RMS (ERMS), Alveolar RMS (ARMS), and anaplastic or undifferentiated. ERMS and ARMS comprise the vast majority of cases that affect the genitourinary system. More recently molecular classification has aided patient stratification based on risk categories as will be explained below.
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