Hematol Oncol Stem Cell Ther 1(2) April 2008 hemoncstem.edmgr.com 133 Soft tissue sarcomas are the sixth most common malignancy in childhood and rhabdomyosarcot mas constitute about 50% of soft tissue sarcot mas. This tumor accounts for 10% to 15% of solid mat lignant tumors and 6% of all malignancies in children under 15 years of age. In the United States, the malet totfemale ratio is 1.5:1, and the tumor is twice as comt mon in whites as in AfricantAmericans. Approximately 250 new cases are diagnosed every year.1 Rhabdomyosarcoma is a malignant tumor of strit ated muscle but, because of its mesenchymal origin, can originate in tissue that does not normally contain striated muscle (for example, the ureter). There is a bit modal distribution of rhabdomyosarcoma with peaks between 2 and 4 years of age and 12 and 16 years of age. Nearly 80% of rhabdomyosarcoma is diagnosed by the age of 14 years. The most common primary sites for rhabdomyosarcomas include the head and neck, the genitourinary tract, and extremities. However, primary sites with a favorable prognosis include the orbit and nonparameningeal, head and neck, paratestis, the vat gina, and the biliary tract.2,3