Which patients with microscopic disease and rhabdomyosarcoma experience relapse after therapy? A report from the soft tissue sarcoma committee of thechildren's oncology group

Purpose: To identify which patients with rhabdomyosarcoma and microscopic r esidual disease (group II) are likely to not respond to therapy. Patients and Methods: Six hundred ninety-five patients with group II tumors received. chemotherapy and 90% received radiation therapy on Intergroup Rh abdomyosarcoma Study (IRS)-I to IRS-IV (1972 to 1997). Tumors were subgroup ed depending on the presence of, microscopic residual disease only (subgrou p IIa), resected positive regional lymph nodes, (subgroup IIb), or microsco pic residual disease and resected positive regional lymph nodes (subgroup I Ic). Results: Overall, the 5-year failure-free survival rate (FFSR) was 73%, and patients with embryonal rhabdomyosarcoma treated on IRS-IV fared especiall y well (5-year FFSR, 93%; n = 90). Five-year FFSRs differed significantly b y subgroup (IIa, 75% and n = 506, IIb, 74% and n = 101; IIc, 58% and n = 88 ; P = .0037) and treatment (IRS-I, 68%; IRS-II, 67%; IRS-III, 75%; IRS-IV, 87%, P < .001). Multivariate analysis revealed positive associations betwee n primary site (favorable), histology (embryonal), subgroup IIa or IIb, tre atment (IRS-III/IV), and better FFSRs. Patterns of treatment failure reveal ed local failure to be 8%, regional failure, 4%, and distant failure, 14%. The relapse pattern noted over the course of IRS-I to IRS-IV shows a decrea se in the systemic relapse rates, particularly for patients with embryonal histology, suggesting that improvement in FFSRs is primarily a result of im proved chemotherapy. Conclusion: Group II rhabdomyosarcoma has an excellent prognosis with conte mporary therapy as used in IRS-III/IV, and those less likely to respond can be identified using prognostic factors: histology, subgroup, and primary s ite. Patients with embryonal rhabdomyosarcoma are generally cured, although patients with alveolar rhabdomyosarcoma or undifferentiated sarcoma, parti cularly subgroup IIc at unfavorable sites, continue to need better therapy.