Soft tissue sarcomas in children are relatively rare. Approximately 850 to 900 children and adolescents are diagnosed each year with rhabdomyosarcoma (RMS) or one of the non-RMS soft tissue sarcomas (NRSTS). Of these, 350 are cases of RMS. RMS is the most common soft tissue sarcoma in children 14 years old and younger, and NRSTS is more common in adolescents and young adults. Infants also get NRSTS, but their tumors constitute a distinctive set of histologies, including infantile fibrosarcoma and malignant hemangiopericytoma, not seen in adolescents. Surgery is a major therapeutic modality for all pediatric soft tissue sarcomas, and radiation can play a role in the local therapy for these tumors. RMS is always treated with adjuvant chemotherapy, whereas chemotherapy is reserved for the subset of NRSTS that are high grade or unresectable. This review discusses the etiology, biology, and treatment of pediatric soft tissue sarcomas, including new approaches to therapy aimed at improving the dismal prognosis of patients who have recurrent and metastatic disease.
Rhabdomyosarcoma EpidemiologyRMS is the most common soft tissue sarcoma among children less than 15 years old, with an incidence of 4.6 per million per year [1]. This represents 50% of all soft tissue sarcomas in this age range. It is slightly more common in boys than in girls, with a ratio of 1. slightly more common in white children than in black children less than 5 years old (1.1:1) but is more common in black children than in white children 5 years of age or older (1.2:1). Over the past 30 years, the incidence of RMS in the pediatric age group has been constant [1].
EtiologyLittle is known about the etiology of RMS. A few cases are associated with Li-Fraumeni syndrome (caused by germline mutations in p53) [2] or with neurofibromatosis (caused by mutations in NF1) [3]. There also is a weak association with congenital anomalies, especially in boys [4]. These tumors sometimes are seen as second malignant neoplasms after radiation therapy.
Molecular and cellular biologyThere are two major histologic variants of RMS-embryonal and alveolar. Other, minor, histologic types include spindle cell, botryoid, and pleomorphic. Embryonal RMS is named for its resemblance to immature skeletal muscle, accounts for 60% of RMS cases in patients less than 20 years of age, and tends to arise in the head and neck region, orbits, and genitourinary region (including bladder and prostate). Alveolar RMS, named for its resemblance to normal lung parenchyma, arises predominantly in the head and neck region and the extremities [3]. Histologically, RMS is a small round blue cell tumor, characterized by expression of muscle-specific antigens, such as desmin and MyoD, and by the presence of eosinophilic rhabdomyoblasts on standard pathologic staining.Alveolar RMS is characterized by the presence of one of two recurrent chromosomal translocations: t(2;13)(q35;q14), seen in 55% of cases, or t(1;13)(p36;q14), seen in 22% of cases [5]. These fuse the FKHR gene on chromosome 13 with...