Rhabdomyosarcoma (RMS) has three known subtypes including: Embryonal, Alveolar, & Pleiomorphic each with distinct characteristics.
Embryonal RMS has a predilection for the ages of 0-15 years and predominates in males. This type is mostly found about the head and neck but the botryoid variants (meaning “cluster of grapes” after its usual gross appearance) are commonly found in the vagina. Akin to the embryonal subtype is the Alveolar RMS; which predominates in males in the 10-25 years range. Also found mostly in the head and neck, this subtype can occur in the thigh and calf. Histologically, these tumors appear as small round blue cells that will frequently have muscle striations and can be differentiated by special stains that highlight actin (Figure 16). MRI is the best study to delineate the extent of these soft tissue tumors. Treatment of these tumors involves chemotherapy before and after wide excision of the tumor. Post-operative XRT is only undertaken if margins are positive following excision. The most current chemotherapeutics include vincristine, dactinomycin, cyclophosphamide, and doxorubicin; these agents have been highly effective in improving 5-year survival from 10% to 80%. However, the prognosis with alveolar RMS is worse than embryonal.
Figure # 16
Micrograph of rhabdomyosarcoma with special staining to show the muscle fibers within the tumor.
The rare Pleiomorphic RMS does not have a predilection for younger patients and instead attacks older adults. It usually involves the proximal extremities and carries a poor prognosis. Histologically, bizarre giant cells and tadpole myoblasts are usually encountered that stain strongly for actin, myosin and glycogen. Metastatic rates are high and treatment consists of wide excision and adjuvant XRT, as the results with chemotherapy have been disappointing.