Pattern of Relapse and Treatment Response in WNT-Activated Medulloblastoma

Wingless-activated (WNT) medulloblastoma have been identified over the past decade as being a candidate for therapy de-escalation based on their excellent survival, however a paucity of relapses in any single cohort have precluded any additional analysis of markers of relapse.  To address this gap in knowledge, an international cohort of 91 WNT-MB was assembled where we identified 14 relapsed cases where five-year progression free survival was 0.84 (95% 0.763-0.925). Maintenance chemotherapy was identified as a strong predictor of relapse, where no relapses were observed in cases receiving high doses of cyclophosphamide or ifosphamide (p=0.0026). The location of relapse was metastatic in 10/14 of relapses, with 7/10 metastatic relapses presenting along the ependymal lining in the lateral ventricles. Maintenance chemotherapy, specifically cumulative cyclophosphamide dose is a significant predictor of relapse across WNT-MB.  Future efforts to de-escalate therapy need to carefully consider not only the radiation dose but also the chemotherapy regimen, and the propensity to metastatic relapses.