Rhabdomyosarcoma

Rhabdomyosarcoma is the most common malignant soft tissue tumor of children and young adults. It is an uncommon tumor in adults over the age of 30.  Males are affected slightly more than females. More than half the cases occur below the age of 10 years.

The malignant cells of this tumor have features characteristic of developing skeletal muscle. Although rhabdomyosarcoma can appear in the extremities, it is more frequently seen in other areas: the head and neck region, the vaginal area in females, the testicular area in males, or the bladder and prostate. Most commonly the disease presents as a painless mass. It can also be diagnosed secondary to bleeding or pain at the site. Sometimes the tumor will present as a grape-like mass, somewhat unique among the soft tissue tumors.

Epidemiology

Prognosis for most of those diagnosed with rhabdomyosarcoma has improved significantly in the last 30 years. Overall survival rates have improved from 25% to more than 70% in recent reports. Prognosis is influenced by the primary site of disease, the extent of disease and the histologic subtype. Favorable primary sites include the orbit, the head and neck region (except the areas near the lining of the nervous system), the vagina and the area near the testis. The extent of the disease, particularly after surgery, is also important. Those who have surgery which completely or almost completely removes all tumors have a better outlook than those who have significant disease remaining after surgery.

Most rhabdomyosarcomas occur without predisposing risk factors. In some cases these tumors are associated with a genetic predisposition to cancer such as the Li-Fraumeni syndrome.

Rhabdomyosarcoma can involve regional lymph nodes at a higher rate than other soft tissue sarcomas, and this can impact on prognosis as well. Children who present with metastatic disease at diagnosis (approximately 20% of cases) fare less well, but those with limited metastatic sites (two or fewer) and favorable histology can have survival rates approaching 40%. With regard to histology, embryonal rhabdomyosarcoma has a more favorable prognosis than the alveolar subtype.

Treatment and Follow-up for Localized Disease

Treatment for local disease includes a combination of chemotherapy and surgery. Radiation may also be employed when complete tumor resection has not been possible. Chemotherapy is indicated for all patients with rhabdomyosarcoma, but the amount of chemotherapy and the duration of treatment can vary depending on risk factors. The drugs which have demonstrated activity in rhabdomyosarcoma include vincristine, actinomycin, cyclophosphamide, ifosfamide, doxorubicin, carboplatin, etoposide, irinotecan and topotecan. These drugs are given in various combinations dependent on disease evaluation. The two drug regimen, vincristine and actinomycin, is employed for those with a favorable prognosis, and alternate two or three drug combinations are used in other settings.

Treatment and Follow-up for Metastatic Disease

Metastatic disease most commonly occurs in the lungs, lymph nodes or bone marrow but many other locations are possible. Metastatic disease developing after initial treatment or locally recurrent disease is still treatable, but the outcome is generally less favorable and particularly for those with metastatic disease the overall prognosis is guarded. The role of intensive regimens utilizing bone marrow or peripheral blood stem cells is unproven at this time.

When rhabdomyosarcoma occurs in adults, it is generally the pleiomorphic subtype which portends a less favorable prognosis. Treatment can be given in a manner similar to the regimens used in children, although actinomycin is less commonly used in the adult population.

Targeted Therapies

No specific targeted therapies exist for rhabdomyosarcoma at present. Specific chromosomal translocations which give rise to different fusion proteins have been delineated for alveolar rhabdomyosarcoma and these are potential targets for future therapies. In addition, these fusion proteins identify patients with differing risks (PAX7-FKHR more favorable than PAX3-FKHR).
Stage 1: Favorable localized disease completely resected
Stage 2: Localized disease at an unfavorable primary site, less than 5 cm in size and without lymph node involvement
Stage 3: Localized disease at an unfavorable primary site and either greater than 5 cm in size or with lymph node involvement.
Stage 4: Metastatic disease at diagnosis

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