Molecular classification of medulloblastoma using immunohistochemistry: A single centre study

Medulloblastoma (MB) is the second most common malignant paediatric central nervous system (CNS) tumour. The World Health Organisation (WHO) advocates an integrated pathological and molecular approach to diagnosis. Immunohistochemistry (IHC) has been proven to be a valid surrogate for molecular subtyping in low resource settings. This study aimed to use IHC to classify MB into different molecular subtypes. Patients diagnosed with medulloblastoma between 2011 and 2021 were included in the study. Clinicopathological characteristics, treatment patterns and outcomes were reviewed. Molecular subgrouping into wingless signalling activated (WNT), sonic hedgehog (SHH), and non-WNT/non-SHH was performed by immunohistochemical staining, using β-catenin, Yes-associated protein 1 (YAP1) and GRB2-Associated Binding Protein 1 (GAB1) antibodies. Of the 32 children evaluated, the mean age at diagnosis was 9.9 years with M: F ratio of 1.5:1. Classic (75.8 %) and desmoplastic/nodular (24.2 %) were the only two histopathological variants reported. Non-WNT/non-SHH constituted the majority of cases (54.5 %), followed by SHH (36.4 %) and WNT subgroups (9.1 %). The 5-year overall survival and 5-year progression-free survival was 41 % and 38 % respectively. The 30-day operative mortality rate was 28.1 %. Molecular subgroups determined by immunohistochemistry, can be easily incorporated into routine practice in low resource settings. The overall survival rate in our cohort is lower than thate reported in the literature due to high post-operative mortality and low uptake of adjuvant oncotherapy.