Molecular subgroups of medulloblastoma: the current consensus

Abstract

Medulloblastoma, a small blue cell malignancy of the cerebellum, is a major cause of morbidity and mortality in pediatric oncology. Current mechanisms for clinical prognostication and stratification include clinical factors (age, presence of metastases, and extent of resection) as well as histological subgrouping (classic, desmoplastic, and large cell/anaplastic histology). Transcriptional profiling studies of medulloblastoma cohorts from several research groups around the globe have suggested the existence of multiple distinct molecular subgroups that differ in their demographics, transcriptomes, somatic genetic events, and clinical outcomes. Variations in the number, composition, and nature of the subgroups between studies brought about a consensus conference in Boston in the fall of 2010. Discussants at the conference came to a consensus that the evidence supported the existence of four main subgroups of medulloblastoma (Wnt, Shh, Group 3, and Group 4). Participants outlined the demographic, transcriptional, genetic, and clinical differences between the four subgroups. While it is anticipated that the molecular classification of medulloblastoma will continue to evolve and diversify in the future as larger cohorts are studied at greater depth, herein we outline the current consensus nomenclature, and the differences between the medulloblastoma subgroups.

Fig. 1

Dendrogram depicting the classification of embryonal tumors of the cerebellum. Medulloblastomas should be differentiated from the less common ATRTs and ETANTRs of the cerebellum. Under the current consensus classification of medulloblastoma four principle subgroups are identified: Wnt, Shh, Group 3, and Group 4. The evidence suggests that each of the four principle subgroups will likely have distinct ‘subsets’ that are biologically and clinically homogeneous as compared to other subsets from within the same subgroup. As the nature and number of subsets for each subgroup are currently unknown, the consensus classification suggests that each subset be named using a Greek letter (α, β, γ, etc.) until such time as they are sufficiently characterized to be named based on their molecular etiology

Fig. 2

Comparison of the various subgroups of medulloblastoma including their affiliations with previously published papers on medulloblastoma molecular subgrouping