The Medulloblastoma Microenvironment: Developmental Niches, Cellular Crosstalk and Therapeutic Opportunities

Medulloblastoma is increasingly best understood not simply as a cell-autonomous embryonal tumour, but as a family of molecularly and anatomically distinct diseases shaped by the developing cerebellum and posterior fossa. The four principal molecular subgroups—WNT, sonic hedgehog, Group 3 and Group 4—differ not only in genetics and outcome, but also in barrier permeability, immune composition, stromal crosstalk and routes of dissemination. Histopathological variation likewise reflects differences in tumour architecture, neuronal maturation and cytological aggressiveness that intersect with, but are not reducible to, molecular subgroup. This review takes a microenvironment-centred view of medulloblastoma biology. It asks how non-malignant cells, fluid compartments and physical interfaces—including immune cells, the choroid plexus and cerebrospinal fluid, the blood–brain and blood–tumour barriers, astrocytes and experimental model systems—modify tumour initiation, progression, therapy response and relapse. The central argument is that the medulloblastoma tumour microenvironment is not merely sparse or passive; instead, pathological, spatial and molecular analyses of human tumours, complemented by models that preserve the relevant niche, reveal a developmentally patterned, subgroup-specific and therapeutically tractable ecosystem.