Rhabdomyosarcoma

Epidemiology
Most common pediatric soft tissue sarcoma; 300-400 cases per year in US
Bimodal age distribution (ages 2-6 and second peak in adolescence)

Risk factors
Male
White
Genetic syndromes: Li-Fraumeni, Gorlin's syndrome; NF

Pathology
1) Embryonal
Most common histology
Infants
Intermediate prognosis (85% 5-year PFS)
Orbit, head and neck, GU sites
LOH 11p15.5; EGFR and fibrillin+

2) Alveolar
Second most common histology
Adolescents
Unfavorable prognosis (66% 5-year PFS)
Trunk, retroperitoneum, extremities
t2;13 is characteristic translocation

3) Spindle cell
Separate, favorable subset of embryonal rhabdo (90% 5-yr PFS)
Associated with paratesticular sites

4) Botyroid
Another favorable subset of embryonal tumors (90% 5-yr PFS)
Grape-like appearance
Mucous membranes (GU, ear, biliary tree)

5) Diffuse anaplastic
Rare and unfavorable subtype with 55% 5-year PFS

Prognostic factors
Histology
Stage
Tumor location:
Favorable sites
Orbit (can decrease dose to 45Gy)
Head and neck -- non-parameningeal sites
Paratesticular
Female GU
Unfavorable sites
Parameningeal (nasopharynx, nasal cavity, paranasal sinus, pterygopalatine fossa, infratemporal fossa, middle ear)
Bladder, prostate, perineal
Extremity
Paraspinal
Retroperitoneal
Thoracic


Therapy
Everyone gets chemo, even after complete resection
Surgery: Fewer than 20% of patients can have complete resection; 20% have resection with microscopic residual disease; 60% are unresectable/metastatic
Chemo: Most active regimen is VAC (vincristine, dactinomycin, cyclophosphamide); pelvic/unresectable tumors also receive adriamycin/cisplatin
Indications for radiation
Alveolar/undifferentiated histology (regardless of stage)
Any stage II or greater tumor
Doses: hyperfractionation has no proven benefit
Orbital tumors: 45Gy
Microscopic disease: 40-41.4Gy (newest IRS protocol decreasing to 36Gy)
Gross disease: 50.4 - 55.8Gy