Rhabdomyosarcoma is a fast-growing, highly malignant tumor which accounts for over half of the soft tissue sarcomas in children. Less frequently, other soft tissue sarcomas are found in children: fibrosarcoma, mesenchymoma, synovial sarcoma, and liposarcoma.

Rhabdomyosarcoma often causes a noticeable lump on a child's body. If the tumor is located internally, the symptoms depend on its location. For example, tumors in the nasal passage may put pressure on the eustachian tubes; a bladder tumor can cause trouble urinating; an orbital tumor may cause the eye to protrude.

About Rhabdomyosarcoma

Rhabdomyosarcoma tumors arise from a cell called a "rhabdomyoblast", which is a primitive muscle cell. Instead of differentiating into striated muscle cells, the rhabdomyoblasts grow out of control. Since this type of muscle is located throughout the body, the tumors can appear at numerous locations. The four major sites in which rhabdomyosarcoma is found are:

• head and neck; around the eyes -- 35-40%

• genitourinary tract -- 20%

• extremities -- 15-20%

• trunk (chest and lungs) -- 10-15%

Depending on the "histology" of the cells (how they look under a microscope), the tumors are classified as one of the following:

Embryonal rhabdomyosarcoma. Most common type, usually found in children under 15 and in the head and neck region and genitourinary tract.

Botryoid type. A variant of the embryonal type; the tumor arises as a grape-like lesion in mucosal-lined hollow organs such as the vagina and urinary bladder.

Alveolar type. A more aggressive tumor which usually involves the muscles of the extremities or trunk.

Pleomorphic type. Usually seen in adults and arises in muscles of the extremities.

Embryonal rhabdomyosarcoma is considered the most treatable form of the disease. The prognosis is also affected by the location of the primary tumor. Orbital and genitourinary track rhabdomyosarcomas have a better prognosis than do tumors which originate in the head and neck, extremity, pelvic, and trunk locations.

Prognosis also depends on the stage of the tumor. The Intergroup Rhabdomyosarcoma Study Group has defined a set of guidelines, which assign the tumor to groups 1-4 depending on the extent of the disease. For more information, see the PDQ on the staging of rhabdomyosarcoma.