Rhabdomyosarcoma is a very rare tumour, but is important as it is the most common soft tissue sarcoma of childhood, and makes up about 5% of all paediatric malignancies. There are two types seen in childhood: embryonal rhabdomyosarcoma and alveolar rhabdomyosarcoma. Pleomorphic rhabdomyosarcoma is a disease of adults.
Embryonal rhabdomyosarcoma is the most common type of rhabdomyosarcoma in children. It usually occurs before the age of 10 years (80% of cases) and occurrence in adult patients is very rare. Boys have a slightly higher incidence (1.2:1).
Aetiology and Pathogenesis
The exact cause of rhabdomyosarcoma is not known. Embryonal rhabdomyosarcoma is postulated to arise from loss of a gene in chromosome 11p15. Loss of this gene acts in a similar way to RB1 and retinoblastoma via Knudson's two hit hypothesis. Other gene mutations may be seen but are not characteristic (e.g. TP53).
Embryonal rhabdomyosarcoma may arise in any organ or structure of the body. The most common site is the head and neck (50%); about 25% occur in the genitourinary system including the testicle; 10% occur in extremities and the remainder occur in other structures including viscera. The meninges may also be the primary site of disease. Local invasion may be extensive. Lymphatic spread is usually seen only in testicular and peripheral tumours. Haematogenous spread occurs to the lungs.
Symptoms and signs relate to the site of disease. These are usually due to mass effect on adjacent structures (e.g. proptosis, hollow viscous obstruction). Most patients will describe a rapidly growing mass in the history. Imaging demonstrates a heterogenous mass which expands the site of origin and may compress or invade other structures.
Tumour/Normal Tissue Features
The macroscopic appearance depends on the histological subtype. All subtypes are usually large, tan and invade adjacent structures. The botryoid variant displays grape-like projections from a mucosal surface. The spindle cell variant is often firm and has a whorled appearance.
The cells making up an embryonal rhabdomyosarcoma recapitulate the various stages of normal rhabdomyogenesis. Various stages may
Staging / Classification
TNM or other staging system if relevant