Medulloblastoma is a CNS embryonal tumor arising in the cerebellum or dorsal brainstem. It is the most common CNS embryonal tumor and the most common malignant tumor of childhood. Medulloblastoma is classified into molecular groups as well as morphological variants, all with prognostic significance. Molecular profiling has separated medulloblastomas into four principal groups: WNT-activated medulloblastomas (~10%), SHH-activated medulloblastomas (~30%), group 3 medulloblastomas (~20%), and group 4 medulloblastomas (~40%). SHH-activated medulloblastomas with a TP53 mutation (frequently also contain MYCN amplification) and group 3 medulloblastomas with MYC amplification have an abysmal prognosis; both variants commonly demonstrate large cell/anaplastic histology. WNT-activated medulloblastomas with classic histology and infantile SHH-activated and TP53-wildtype medulloblastomas with desmoplastic/nodular or extensive nodularity histology are low-risk tumors.
