Response to therapy

It is unlikely that response to induction chemotherapy or best tumor response during therapy, assessed by anatomic imaging, correlates with the likelihood of survival in patients with rhabdomyosarcoma. This finding was based on the IRSG, COG, and International Society of Pediatric Oncology (SIOP) studies that found no association.[94,95]; [96][Level of evidence C2]; [97][Level of evidence C1] However, an Italian study did find that patient response correlated with likelihood of survival.[54][Level of evidence C1] In patients with embryonal rhabdomyosarcoma who had metastases only in the lungs, the CWS assessed the relationship between complete response of the lung metastases at weeks 7 to 10 after chemotherapy and outcome in 53 patients.[98][Level of evidence C1] The 5-year survival rate was 68% for 26 complete responders at weeks 7 to 10 versus 36% for 27 patients who achieved complete responses at later time points (P = .004).

Other studies have investigated response to induction therapy, showing benefit to response. These data are somewhat flawed because therapy is usually tailored on the basis of response. Thus the situation is not as clear as the COG data suggest.[99-104]

Response as judged by sequential functional imaging studies with fluorine F 18-fludeoxyglucose positron emission tomography (18F-FDG PET) may be an early indicator of outcome [105] and is under investigation by several pediatric cooperative groups. A retrospective analysis of 107 patients from a single institution examined PET scans performed at baseline, after induction chemotherapy, and after local therapy.[105] Standardized uptake value measured at baseline predicted PFS and OS, but not local control. A negative scan after induction chemotherapy correlated with statistically significantly better PFS. A positive scan after local therapy predicted worse PFS, OS, and local control. The COG evaluated the relationship between complete metabolic response, as assessed by 18F-FDG PET imaging, and EFS in patients with intermediate- or high-risk rhabdomyosarcoma.[106][Level of evidence B4] The maximum standard uptake values (SUVmax) at study entry did not correlate with EFS for intermediate-risk (P = .32) or high-risk (P = .86) patients. Compared with patients who did not achieve a complete metabolic response, EFS was not superior for intermediate-risk patients who achieved a complete metabolic response at weeks 4 (P = .66) or 15 (P = .46), or for high-risk patients who achieved a complete metabolic response at weeks 6 (P = .75) or 19 (P = .28). Change in SUVmax at weeks 4 (P = .21) or 15 (P = .91) for intermediate-risk patients and at weeks 6 (P = .75) or 19 (P = .61) for high-risk patients did not correlate with EFS.

PET scans have been shown to be useful in understanding patterns of spread, particularly in patients with extremity disease.[107][Level of evidence C2]