Outcomes of salvage re-irradiation in recurrent medulloblastoma correlate with age at initial diagnosis, primary risk-stratification, and molecular subgrouping.

Purpose: To report outcomes of salvage re-irradiation (re-RT) in recurrent/progressive medulloblastoma (MB).
Methods: Medical records of patients treated with curative-intent re-RT as multi-modality management for recurrent/progressive MB between 2008 and 2018 were analyzed retrospectively.
Results: A total of 28 patients (median age 18 years at index diagnosis) were included. Molecular subgrouping was done using real-time reverse transcriptase polymerase chain reaction (RT-PCR) based on the differential expression of select set of 12 protein coding genes and 9 microRNAs. Fifteen of 17 (88%) patients with sonic hedgehog (SHH)-MB developed isolated local recurrence within the index tumor-bed, while 5 of 7 (72%) patients with Group 4 MB developed localized relapse outside the posterior fossa. Diffuse neuraxial dissemination was seen in 2 patients with SHH-MB, and one each of Group 4 and wingless (WNT)-MB. Molecular subgrouping was not known in 3 patients. The dose and volume of re-RT was based on site and patterns of relapse, comprising unifocal in 18 (64%), multi-focal in 3 (11%), and repeat craniospinal irradiation (re-CSI) in 7 (25%) patients. Median interval from primary irradiation to re-RT was 49.5 months (range 24-98 months) with median cumulative biologically effective dose of 117 Gy (range 78-132 Gy). All patients received platinum-based salvage chemotherapy either before or after re-RT. One patient developed symptomatic radiation necrosis following re-CSI. At a median follow-up of 24 months (range 6-84 months), 2-year post-re-RT progression-free survival (PFS) and overall survival (OS) was 46% and 51% respectively. Younger age (< 18 years) at index diagnosis, primary risk stratification (standard-risk) and molecular subgrouping (Group 4) were associated with significantly better post-re-RT outcomes.
Conclusion: Salvage re-RT provides good local control and encouraging survival outcomes with acceptable toxicity in selected patients with recurrent/progressive MB.