Medulloblastoma, group 4

Last revised by Frank Gaillard on 01 Feb 2022

Medulloblastoma - group 4 tumors are malignant tumors of the central nervous system, and one of the most common pediatric tumors. They are the most common medulloblastoma group (followed by group 3, SHH-activated, and WNT-activated), and typically arise from the vermis of the cerebellum. 

The nomenclature and classification of medulloblastomas are rapidly evolving. In the 5th edition (2021) of the WHO classification of CNS tumors, group 3 and group 4 medulloblastomas are grouped together under non-WNT/non-SHH tumors, which is in turn divided into 8 subgroups 5

Group 4 tumors account for approximately 34-40% of all medulloblastomas, and have a predilection for males, with a 2:1 male to female ratio 1,4.

They are most frequently encountered in children (4-16 years of age), not infrequently in adults (second only to SHH in frequency) and are uncommon in infants 1

The majority of grade 4 tumors are of classic histology, with the rest being of large cell / anaplastic histology 2

The radiographic features of group 4 tumors are those that we typically associate with medulloblastomas; midline masses arising from the vermis. They are fairly well defined with limited contrast enhancement 3

For more details on radiographic features, please refer to the general article on medulloblastomas.  

Surgery is the first line of therapy (as is the case in all groups) with the aim being histological proof, molecular subtyping and maximal tumor resection, with adjuvant therapy depending on an overall risk profile (see general article on medulloblastoma) 2

The incidence of CNS metastatic disease in Group 4 tumors at diagnosis is common, found in 31% of all cases, and is even more frequent in infants (36%) 1

Overall, group 4 tumors have a poor prognosis, somewhat better than group 3 tumors, but significantly worse than SHH and WNT subtypes 1,2. In adults, the prognosis is very poor, whereas in children it is intermediate 4

Prognosis is also influenced by histological subtype, with large cell/anaplastic histology having a worse prognosis 2.

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