Historically, medulloblastoma had been segregated into four molecular subgroups: i) WNT-activated, ii) sonic hedgehog (SHH)-activated, iii) group 3, and iv) group 4. ¹ Indeed, these subgroupings were the basis for a major diagnostic restructuring which was introduced in the 2016 World Health Organization (WHO) classification of CNS tumors. ² The 2021 classification guidelines further revised these subgroups to acknowledge the evolving knowledge of their clinical and biological heterogeneity. ³ Here, they are segregated based on their molecular or histological features. Included in the “medulloblastoma, molecularly defined” category are: i) Medulloblastoma, WNT-activated, ii) Medulloblastoma, SHH-activated and TP53-wildtype, iii) Medulloblastoma, SHH-activated and TP53-mutant, and iv) Medulloblastoma, non-WNT/non-SHH. Importantly, recent large-scale epigenetic and transcriptomic studies have uncovered further refinements beyond the 4 original molecular subgroups. ^4-6 The clinical utility of these refinements is still currently being investigated and may be incorporated in a later amendment or edition of the classification guidelines.