Rhabdomyosarcoma

I. Epidemiology and etiology

Rhabdomyosarcoma is the most common soft tissue sarcoma in the pediatric age group; there are approximately eight cases per million population. Suggestive evidence of C particle viruses in these tumors has been observed with electron microscopy but the viruses have not been isolated.

II. Pathology and natural history

A. Histology

Four major histologic categories of this striated muscle neoplasm have been described: embryonal (including sarcoma botryoides), alveolar, pleomorphic, and mixed. Z bands can be seen with electron microscopy. Rhabdomyoblasts have acidophilic cytoplasm, which is often PAS-positive.

B. Sites

The head and neck are involved in 35 percent of cases, the trunk and extremities in 35 percent, and the genitourinary tract in 30 percent.

C. Mode of spread

These tumors have a great tendency to recur locally and to metastasize early via the venous and lymphatic systems. Any organ may be involved with metastases.

III. Diagnosis

A. Symptoms

The most common presenting symptom is a painless, enlarging mass. Hematuria and urinary tract obstruction is seen with primary tumors of the genitourinary tract. The painless swelling is often noticed after minor trauma that calls attention to the enlarging mass.

B. Physical findings

Physical findings include mass lesions, urinary tract obstruction, and a "cluster of grapes" protruding through the vaginal canal (sarcoma botryoides). Exophthalmos or proptosis occurs with head and neck primaries.

C. Laboratory studies

1. CBC, LFTs

2. Plain x-ray films and MRI CT scans of involved areas

3. Bone marrow aspiration and biopsy

4. Gallium (and perhaps thallium) scans

IV. Staging system and prognostic factors

A. Intergroup Rhabdomyosarcoma Study Staging System

Stage Extent of disease

I Localized disease, completely resected

II Localized disease, microscopic residual tumor

IIA Grossly resected disease with microscopic residual tumor and negative lymph nodes

IIB Regional disease, completely resected, with no microscopic residual disease

IIC Regional disease with positive lymph nodes, grossly resected

III Incomplete resection or biopsy with residual gross disease

IV Distant metastases

B. Survival and prognostic factors

Survival is closely correlated with stage. The five-year survival with the standard VAC chemotherapy regimen is almost 100 percent for stages I and II, greater than 60 percent for stage III, and about 40 percent for stage IV. The overall survival rate is 70 percent.

V. Management

The treatment of rhabdomyosarcoma should be aggressive, even with localized disease. Surgery, RT, and chemotherapy should be used for all cases with any residual disease.

A. Surgery

Surgery should include total excision, if possible, but very radical surgery is unnecessary and unwarranted. Lymph node dissection is useful for staging in extremity or genitourinary tract tumors.

B. RT

RT usually consists of 5000 to 6000 cGy in five to six weeks to the primary tumor site with wide ports so as to include margins of all dissected tumors.

C. Chemotherapy

A regimen that includes vincristine, actinomycin D, and cyclophosphamide (VAC) is most commonly given. Current studies are comparing Adriamycin, etoposide, and ifosfamide to VAC for advanced disease. Chemotherapy is necessary for patients:

1. Adjuvantly with stage I disease

2. With RT for stage II disease, and

3. To shrink the primary tumor either before or after surgery for stage III and IV disease and continued as adjunctive therapy