Omission of Upfront Craniospinal Irradiation in Patients with Low-Risk WNT-Pathway Medulloblastoma Is Associated with Unacceptably High Risk of Neuraxial Failure.

Abstract

Medulloblastoma is a heterogenous disease comprising four molecular subgroups: wingless (WNT), sonic hedgehog (SHH), group 3, and group 4, respectively. Excellent long-term outcomes have prompted deintensification of therapy in WNT-pathway medulloblastoma. We assessed the safety of avoiding upfront craniospinal irradiation (CSI) in children with low-risk WNT-pathway medulloblastoma. Children with low-risk WNT-pathway medulloblastoma were treated with postoperative focal conformal radiotherapy, avoiding upfront CSI, followed by six cycles of adjuvant systemic chemotherapy. A group-sequential design (triangular test) with predefined stopping rules if the rate of relapse exceeded 15% at 2 years was incorporated to ensure the safety of study participants. 7 children with low-risk WNT-pathway medulloblastoma were accrued after written informed consent/assent and treated as per protocol. One child died of neutropenic sepsis and multiorgan dysfunction during chemotherapy. Three children were detected with neuraxial failure (supratentorial brain and/or spine) on surveillance neuro-imaging within 2 years from index diagnosis, leading to premature study termination. At relapse, children were treated with salvage CSI plus boost irradiation of metastatic deposits followed by second-line chemotherapy. Two of them continue to be in remission (32 and 26 months after first relapse), while one child developed a second relapse, necessitating further systemic chemotherapy and craniospinal reirradiation, resulting in excellent clinico-radiologic response. At a median follow-up of 42 months, the 2-year Kaplan-Meier estimates of event-free survival, recurrence-free survival, and overall survival were 42.9%, 50%, and 85.7% respectively. Omission of upfront CSI in low-risk WNT-pathway medulloblastoma is associated with an unacceptably high risk of neuraxial failure. See related commentary by Remke and Ramaswamy, p. 4161.