Rhabdomyosarcoma
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.
