Assessment of response to induction therapy and its influence on 5-year failure-free survival in group III rhabdomyosarcoma: The intergroup rhabdomyosarcoma study-IV experience - A report from the soft tissue sarcoma committee of the children's oncology group

Purpose Initial response to induction chemotherapy predicts failure-free survival (FFS) in osteosarcoma and Ewing's sarcoma. For Intergroup Rhabdomyosarcoma Study (IRS) IV patients with group III rhabdomyosarcoma, we assessed whether reported response assessed by anatomic imaging at week 8 predicted FFS. Patients and Methods We studied 444 group III patients who received induction therapy, had response assessed at week 8 by anatomic imaging, and continued with protocol therapy. Induction chemotherapy was generally followed by radiation therapy (RT) starting after week 9. Response to induction therapy was determined at weeks 0 and 8. Local institutions coded response. Results Response rate for the entire cohort at week 8 was 77% (95% CI, 73% to 81%; complete response [CR], 21%; partial response [PR], 56%) but response had no influence on FFS (P = .57). Two hundred seventy-two patients received standard-timing RT at week 9 and thus only chemotherapy during induction. Response rate was 81% (95% CI, 76% to 86%; CR, 22%; PR, 59%). In these patients, response did not influence FFS except for those with alveolar histology. One hundred thirty-two other patients received chemotherapy and RT during induction (up-front RT). Response rate was 65% (95% CI, 57% to 73%; CR, 12%; PR, 53%), but response had no influence on FFS (P = .69). Forty patients received no RT at all (protocol violation) and response to induction therapy had no effect on FFS. Conclusion In IRS-IV, response rate to induction therapy was 77% in group III patients, was independent of histology, and had no influence on FFS overall.