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Rhabdomyosarcoma Cancer Panel
Rhabdomyosarcoma is a soft tissue sarcoma arising from skeletal muscle tissue (NCI 2012). Rhabdomyosarcoma most often affects children, and it is the most common soft tissue sarcoma diagnosed in children (SEER 1999). Approximately 350 cases of rhabdomyosarcoma are diagnosed in children each year, making up about 50% of pediatric soft tissue sarcoma cases and 7.4% of pediatric cancers (SEER 1999). Survival rates depend on age at diagnosis, stage, histology, and site of origin (NCI 2012). Overall, the 5-year survival rate for childhood rhabdomyosarcoma is 64% (SEER 1999).
Rhabdomyosarcoma can occur anywhere in the body: most commonly, the head, genitourinary tract, and the arms and legs (NCI 2012). There are three main rhabdomyosarcoma histologies: embryonal (60-70% of childhood rhabdomyosarcomas), alveolar (~20%), and pleomorphic (anaplastic; rare in children; NCI 2012). Treatment of rhabdomyosarcoma includes chemotherapy for all patients, surgery whenever possible, and radiation therapy in most cases (patients who have not had surgery and those whose tumors were not completely resected; NCI 2012).
Embryonal and alveolar rhabdomyosarcoma histologies have distinct molecular profiles: 80% of alveolar rhabdomyosarcomas harbor a characteristic translocation between chromosomes 1 or 2 and chromosome 13, resulting in a PAX7:FOXO1 or a PAX3:FOXO1 fusion protein (NCI 2012). The clinical behavior of alveolar rhabdomyosarcomas without translocations are more similar to typical embryonal rhabdomyosarcomas than to alveolar rhabdomyosarcomas with translocations. The impact of tumor genetics in rhabdomyosarcoma on treatment is not well understood. ALK has been suggested as a potential therapeutic target in rhabdomyosarcoma (van Gaal et al. 2012). Aberrant genes observed in embryonal rhabdomyosarcoma include BRAF, CTNNB1 (beta-catenin), FGFR4, HRAS, KRAS, NRAS, PIK3CA, and PTPN11. KRAS mutations have been found in alveolar rhabdomyosarcoma (Shukla et al. 2012 ).