The most common type of Rhabdomyosarcoma is
Rhabdomyosarcoma, the most common soft-tissue sarcoma of childhood and adolescence, usually appears before age 20. It may arise in any anatomic location, but most occur in the head and neck or genitourinary tract, where there is little if any skeletal muscle as a normal constituent. Rhabdomyosarcoma is histologically sub classified into embryonal, alveolar, and pleomorphic variants. The rhabdomyoblast—the diagnostic cell in all types—contains eccentric eosinophilic granular cytoplasm rich in thick and thin filaments. Rhabdomyoblasts may be round or elongate; the latter are known as tadpole or strap cells, and may contain cross-striations visible by light microscopy.
Embryonal rhabdomyosarcoma is the most common type, accounting for 60% of rhabdomyosarcomas. It includes the sarcoma botryoides as well as spindle cell and anaplasticvariants. The tumor occurs in children younger than 10 years of age and typically arises in the nasal cavity, orbit, middle ear, prostate, and paratesticular region. This variant of rhabdomyosarcoma commonly has parental isodisomy of chromosome 11p15.5, which leads to overexpression of the imprinted IGFII gene. The sarcoma botryoides subtype develops in the walls of hollow, mucosal-lined structures, such as the nasopharynx, common bile duct, bladder, and vagina. Where the tumors abut the mucosa of an organ, they form a submucosal zone of hypercellularity called the cambium layer.
Embryonal
Alveolar
Pleomorphic
Inflammatory