Pediatric soft tissue sarcomas are a heterogeneous group of tumors that are presumed to arise from a primitive mesenchymal cell. These tumors can arise in many anatomic locations and can resemble fat, fibrous tissue, and muscle. Overall, these pediatric tumors are rare, accounting for about 7 percent of all childhood cancers; they have an estimated incidence of 11 per million .
This topic review will cover the epidemiology, pathology, and pathogenesis of two specific types of pediatric soft tissue sarcoma, rhabdomyosarcoma (RMS) and undifferentiated sarcoma (UDS). Clinical manifestations, the diagnostic evaluation, staging and risk-adapted therapy for RMS and UDS are discussed elsewhere, as are primary tumors of bone, and other soft tissue neoplasms arising in children as well as adults. (See appropriate topic reviews).
RMS is the most common soft tissue tumor of childhood, and responsible for approximately one-half of all soft tissue sarcomas in this age group [1,2]. However, they are rare, representing only 3 to 4 percent of pediatric cancers overall. Approximately 350 new cases are diagnosed in the US each year, and the annual incidence in children, adolescents, and young adults under the age of 20 is 4.3 cases per one million population .
Two-thirds of cases are diagnosed in children younger than six years of age, and there is a small male predominance (male to female ratio between 1.3 and 1.5). The incidence in African-American patients is higher than in whites, most notably in 15 to 19 year olds . The incidence appears to be lower in Asians when compared to predominantly Caucasian populations .
Although RMS can arise anywhere in the body, distinct patterns link primary site, histology, and age at diagnosis: