Despite its name, rhabdomyosarcoma does not necessarily arise from skeletal muscle. In fact, it commonly arises in tissue that contains no skeletal muscle. Unlike most other cancers, the approach to treatment and the prognosis of rhabdomyosarcomas vary greatly depending on the site of origin, with certain sites being considered favorable and others unfavorable. This characterization mostly correlates with the histologic subtype – tumors that arise in favorable sites are usually embryonal, while those from unfavorable sites are typically alveolar. So important is the site of origin that it is a primary factor in determining tumor stage. Rhabdomyosarcomas that arise within hollow organs such as the bladder, nasal cavity, or biliary tree are often described as botryoid (“cluster of grapes”), which is a type of embryonal and associated with the best prognosis. Age is also an important prognostic factor but mostly because it correlates with histology and site or origin: in general, children under 1 year of age and older than 10 have a worse prognosis. Like other small round blue cell tumors (lymphoma, Ewing’s/PNET, neuroblastoma), rhabdomyosarcomas have a tendency to metastasize to the bone marrow, which is why bone marrow biopsy is always performed as part of the initial work up.
Tumors in favorable sites are treated with biopsy and neoadjuvant chemotherapy with little need for more than a limited surgical exploration to confirm the absence of residual tumor. Complete resection with a margin is rarely needed. Unfavorable tumors, on the other hand, require elaborate attempts at local control with either aggressive surgery or, if surgical resection is not feasible or safe, external beam radiation. Multiple operative attempts to render the patient free of tumor might be reasonable in certain situations. For certain sites, such as an extremity or the trunk, sentinel lymph node biopsy is often requested. The technique is straightforward and should include both lymphoscintigraphy and injection of blue dye. Often two lymph nodes are identified, sometimes in different nodal regions (popliteal and inguinal), both of which need to be excised.
At second- or third-look operations for resection, the previous scar and all tissue planes violated at the previous operation must be excised with a margin, which can result in a significant soft tissue defect. Entering the previous site potentially increases the risk of recurrence but can be difficult to avoid even with preoperative high-resolution three-dimensional imaging. An ideal margin is 1–2 cm; but if the tumor is adjacent to vital structures or bone, a negative tissue fascia plane is acceptable.
Botryoid tumors arising from the vagina should be biopsied and treated with chemotherapy. Mutilating surgery is almost never indicated and the prognosis is usually excellent. Biliary rhabdomyosarcoma also carries a relatively good prognosis, especially if it is of the botryoid variety. Biopsy can be performed through a common duct exploration or through the cystic duct after cholecystectomy. At planned re-operation, we have used choledochoscopy to confirm the absence of residual tumor after chemotherapy. Depending on the stage and extent of disease, some of these patients will also require liver resection or the addition of radiation therapy. Extremity tumors often occur in adolescents, are usually alveolar, and carry a guarded prognosis. Although therapy to control the primary tumor must be aggressive, limb-salvage should be considered if at all possible.