Incidence and Epidemiology
Childhood rhabdomyosarcoma, a soft tissue malignant tumor of mesenchymal origin, accounts for approximately 3.5% of the cases of cancer among children aged 0 to 14 years and 2% of the cases among adolescents and young adults aged 15 to 19 years.[3,4] The incidence is 4.5 per 1 million children and 50% of cases are seen in the first decade of life.
Incidence may depend on the histologic subtype of rhabdomyosarcoma:
- Embryonal: Patients with embryonal rhabdomyosarcoma are predominantly male (M:F = 1.5) and peaks in the 0 to 4 year age group at approximately 4 cases per 1 million children, with a lower rate in adolescents, approximately 1.5 cases per 1 million adolescents.
- Alveolar: The incidence of alveolar rhabdomyosarcoma does not vary by gender and is constant from ages 0 to 19 years at approximately 1 case per 1 million children and adolescents.
- Undifferentiated sarcoma: Infants younger than 1 year have a higher incidence of undifferentiated sarcoma and tumors of the trunk and abdomen and a lower incidence of parameningeal tumors than do older patients.
The most common primary sites for rhabdomyosarcoma are the head, the genitourinary tract, and the extremities.[7,8] Within extremity tumors, tumors of the hand and foot occur more often in older patients and have an alveolar histology; these tumors also have a higher rate of metastatic spread. Other less common primary sites include the trunk, chest wall, perineal/anal region, and abdomen including the retroperitoneum and biliary tract.
Most cases of rhabdomyosarcoma occur sporadically, with no recognized predisposing factor or risk factor. For patients with embryonal tumors, high birth weight and large size for gestational age are associated with an increased incidence of rhabdomyosarcoma. Genetic conditions associated with rhabdomyosarcoma include Li-Fraumeni cancer susceptibility syndrome (with germline p53 mutations),[12,13,14] pleuropulmonary blastoma (with DICER1 mutations),[15,16] neurofibromatosis type I, Costello syndrome (with germline HRAS mutations),[18,19,20,21] Beckwith-Wiedemann syndrome (with which Wilms tumor and hepatoblastoma are more commonly associated),[22,23] and Noonan syndrome.[21,24,25]