Therapy and biomarker dependent progression-free survival in infant sonic hedgehog medulloblastoma: a multi-national retrospective cohort study

Background: Medulloblastoma in infants (iMB; aged < 5 years) presents the challenge of achieving cure while minimising deleterious cranio-spinal irradiation (CSI)-associated late-effects. Non-randomised phase 2 studies have examined upfront CSI omission and chemotherapy intensification for favourable-risk desmoplastic/nodular (DN) tumours associated with the sonic hedgehog (SHH) molecular group (iMB_SHH). Comparison of these therapies in large molecularly defined iMB_SHH cohorts, alongside investigations of prognostic biomarkers in therapy-specific context, is urgently required to define future therapeutic strategies. Methods: In this international retrospective cohort study, a multi-national cohort of molecularly and clinically annotated iMB_SHH was assembled from patient datasets in nine countries. Inclusion criteria was a principal iMB_SHH group classification using DNA methylation array-based classification. Patient cohorts were assigned into upfront treatment groups based on the receipt of radiotherapy (RTx) or chemotherapy (CTx)-only. Upfront RTx treatment groups were assigned as those receiving focal-RTx or CSI. Upfront CTx only regimens used were classified into three groups to reflect disease treatment conventions: standard-dose, high-dose (intensified regimens of sufficient dosage to require stem cell support) and those including intraventricular methotrexate (IVT-MTX). We investigated molecular pathology, upfront treatments, and relationships to outcome, in this real-world setting. Outcomes of interest were progression-free survival (PFS), overall survival (OS), and post-relapse survival (PRS). Findings: Between January 20, 2018 and October 6, 2021, patient data from 267 infants with SHH medulloblastoma were collected from Canada (n = 74), Germany/USA (n = 67), and the UK (n = 54), alongside national cohorts collected from France (n = 26), Italy (n = 4), Japan (n = 20), the Netherlands (n = 11), and Spain (n = 33). 226 patients with PFS and OS data comprised the iMB survival cohort and were split into upfront treatment groups based on the receipt of RTx (n = 74, 33%) or CTx-only (n = 132, 58%). Among iMB_SHH patients treated upfront with CTx-only regimens, IVT-MTX therapy (5-year PFS, 72.6%; n = 72) or high-dose therapy (73.0%; n = 29) achieved PFS outcomes comparable to upfront CSI-based regimens (n = 49; 74.0%; p = 0.51); whereas lower-intensity, standard-dose, chemotherapy-only regimens (n = 31) were inferior (48.4% PFS; p = 0.006). Rescue was common post-relapse after IVT-MTX/high-dose protocols and translated into 5-year OS of 85.6% and 88.6%, respectively. However, information on pattern of relapse and treatments received at recurrence was only available for a small proportion of our cohort (n = 43). The 5-year PFS of patients receiving focal-RTx was (58.2%; n = 25). iMB_SHH encompassed SHH-1 (38%), SHH-2 (47%) and SHH-3 (14%) WHO subgroups. In CSI-naïve iMB_SHH, standard-dose chemotherapy was associated with worse PFS in SHH-1 (p = 0.001), but not SHH-2. Non-DN/MBEN histology (21.2% of iMB_SHH) conferred worse PFS in the upfront CSI-treated and standard-dose (p < 0.001 and p = 0.003, respectively) groups. Metastatic disease only associated with prognosis with upfront IVT-MTX-only therapies (p = 0.013), while established high-risk features of non-infant MB_SHH (TP53-mutation, LCA-histology, MYCN-amplification) only associated with poor prognosis in older SHH-3 (7/7 relapsed). Finally, CSI-naïve PFS findings were validated in a re-evaluation of smaller historical trials cohorts. Interpretation: Our findings show that iMB_SHH outcomes and prognostic biomarkers are therapy dependent. In our retrospective patient group, non-metastatic iMB_SHH treated with high-dose or IVT-MTX chemotherapy-only had equivalent favourable outcomes, independent of histology and subgroup. With outcomes established, clinical trials are now encouraged to focus on quality-of-life following different intensified approaches to identify the kindest curative strategies. Funding: Cancer Research UK, Children with Cancer UK, Children’s Cancer North, Star for Harris, JGW Patterson Foundation, Little Hero and Blue Skye Thinking.