What does a non-response to induction chemotherapy imply in high-risk medulloblastomas?

Purpose: High-risk medulloblastomas (HR-MB) may not respond to induction chemotherapy, with either post-induction stable (SD) or progressive disease (PD). There is no consensus regarding their optimal management. Methods: A retrospective, multicentre study investigated patients with non-responder HR-MB treated according to the PNET HR + 5 protocol (NCT00936156) between 01/01/2009 and 31/12/2018. After two courses of etoposide and carboplatin (induction), patients with SD or PD were analyzed. Upon clinician’s decision, the PNET HR + 5 protocol was either pursued with tandem high-dose chemotherapy (HDCT) and craniospinal irradiation (CSI) (continuation group) or it was modified (switched group). Results: Forty-nine patients were identified. After induction, 37 patients had SD and 12 had PD. The outcomes were better for the SD group: the 5-y PFS and OS were 52% (95% CI 35–67) and 70% (95% CI 51–83), respectively, in the SD group while the 2-y PFS and OS were 17% (95% CI 3–41) and 25% (95% CI 6–50), respectively, in the PD group (p < 0.0001). The PNET HR + 5 strategy was pursued for 3 patients in the PD group, of whom only one survived. In the SD group, it was pursued for 24/37 patients whereas 13 patients received miscellaneous treatments including a 36 Gy CSI in 12 cases. Despite that continuation and switched group were well-balanced for factors impacting the outcomes, the latter were better in the continuation group than in the switched group: the 5-y PFS were 78% (95% CI 54–90) versus 0% (p < 0.001), and the 5-y OS were 78% (95% CI 54–90) versus 56% (95% CI 23–79) (p = 0.0618) respectively. In the SD group, multivariate analysis revealed that MYC amplification, molecular group 3, and a switched strategy were independent prognostic factors for progression. Conclusion: Patients with post-induction SD may benefit from HDCT and CSI, whereas patients with early PD will require new therapeutic approaches.