Rhabdomyosarcoma (RMS) is a rare disease with an incidence in children of 4.5 cases per million per year. Yet, although rare, this is the most common soft tissue sarcoma in children. RMS arises from mesenchymal tissue, which typically differentiates to form striated muscle. Per the World Health Organization 2013 classification, there are now 4 major histologic subtypes of RMS: embryonal, alveolar, pleomorphic, and spindle cell/sclerosing. These subtypes differ significantly in their underlying clinical features and molecular mechanisms. The 2 major subtypes in children are embryonal RMS and alveolar RMS.
Most RMS tumors occur sporadically, more commonly in males, and less commonly in the Hispanic population. There is a bimodal age distribution peaking at age 2 to 6 years and then at age 10 to 18 years. The location of the tumor can occur at almost any anatomical site and varies depending on age and histologic subtype. Younger patients commonly have...
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