MDB-100. Retrospective Analysis of Cumulative Dosing of Chemotherapy Agents and the Effect on Survival in Patients With Average Risk Medulloblastoma Treated on Childrens Oncology Group Study Acns0331

Abstract BACKGROUND Although survival outcomes for average risk (AR) medulloblastoma remain good, patients may experience significant acute and long-term toxicities from therapy. To evaluate the effect of dose modifications among children with AR medulloblastoma, we examined the effect of cumulative chemotherapy dose on overall and event-free survival. METHODS We retrospectively examined the association between the proportion of scheduled chemotherapy dose received on survival outcomes (OS and EFS) using Cox regression models and log-rank tests for patients treated on ACNS0331. We evaluated all chemotherapy agents for the group as a whole and within the four major subgroups. Dose intensity was analyzed continuously and categorically (75% or 75% of planned dose) for each agent. RESULTS 274 evaluable children (medulloblastoma by methylation, received standard dose craniospinal radiation and chemotherapy) were followed for a median of 9.3 years (range, 7.0-10.4 years). Vincristine and cisplatin showed the most variable dose intensity (25.2% and 31.8% of patients received 75% of expected dosing, respectively). Cyclophosphamide and lomustine were not examined due to low dose variability (17.2% and 11.7%, respectively). The effect of dose intensity was evaluated in 235 patients who completed planned therapy. Molecular subgroup remained a significant predictor of outcome in AR medulloblastoma (EFS (p=0.012) and OS (p=0.008)). Although survival curves were lower for less dose intense treatments, no significant difference in EFS or OS was found due to reduced dose intensity for vincristine (p=0.36 EFS, p=0.35 OS) or cisplatin (p=0.49 EFS, p=0.52 OS). The hazard ratio 95% confidence interval for chemotherapy proportion and EFS was 0.9980.977-1.019 (vincristine) and 0.9890.966-1.012 (cisplatin). There was no difference in the effect of dose reductions by molecular subgroup. CONCLUSIONS Moderate reductions in vincristine and cisplatin dose intensity do not significantly affect survival in AR medulloblastoma. It is unknown whether this reduction would reduce chemotherapy-related toxicity.