Medulloblastoma: clinicopathological correlates of SHH, WNT, and non-SHH/WNT molecular subgroups

Abstract

Medulloblastoma is heterogeneous, being characterized by molecular subgroups that demonstrate distinct gene expression profiles. Activation of the WNT or SHH signaling pathway characterizes two of these molecular subgroups, the former associated with low-risk disease and the latter potentially targeted by novel SHH pathway inhibitors. This manuscript reports the validation of a novel diagnostic immunohistochemical method to distinguish SHH, WNT, and non-SHH/WNT tumors and details their associations with clinical, pathological and cytogenetic variables. A cohort (n = 235) of medulloblastomas from patients aged 0.4-52 years was studied for expression of four immunohistochemical markers: GAB1, β-catenin, filamin A, and YAP1. Immunoreactivity (IR) for GAB1 characterizes only SHH tumors and nuclear IR for β-catenin only WNT tumors. IRs for filamin A and YAP1 identify SHH and WNT tumors. SHH, WNT, and non-SHH/WNT tumors contributed 31, 14, and 55% to the series. All desmoplastic/nodular (D/N) medulloblastomas were SHH tumors, while most WNT tumors (94%) had a classic phenotype. Monosomy 6 was strongly associated with WNT tumors, while PTCH1 loss occurred almost exclusively among SHH tumors. MYC or MYCN amplification and chromosome 17 imbalance occurred predominantly among non-SHH/WNT tumors. Among patients aged 3-16 years and entered onto the SIOP PNET3 trial, outcome was significantly better for children with WNT tumors, when compared to SHH or non-SHH/WNT tumors, which showed similar survival curves. However, high-risk factors (M+ disease, LC/A pathology, MYC amplification) significantly influenced survival in both SHH and non-SHH/WNT groups. We describe a robust method for detecting SHH, WNT, and non-SHH/WNT molecular subgroups in formalin-fixed medulloblastoma samples. In corroborating other studies that indicate the value of combining clinical, pathological, and molecular variables in therapeutic stratification schemes for medulloblastoma, we also provide the first outcome data based on a clinical trial cohort and novel data on how molecular subgroups are distributed across the range of disease.

Figures

Fig. 1

GAB1 immunoreactivity. Internodular regions of this D/N medulloblastoma show strong cytoplasmic staining for GAB1, but negligible reactivity within nodules (a). In contrast, this paucinodular tumor shows GAB1 reactivity in both anatomic compartments (b). Some anaplastic tumors are also GAB1-positive (c). Non-SHH tumors are GAB1-negative (d)

Fig. 2

β-Catenin immunoreactivity. Most WNT pathway medulloblastomas show combined cytoplasmic and nuclear immunoreactivity (a), though some genuine WNT tumors show variable nuclear staining (b, c). Medulloblastomas that contain scattered nucleopositive cells amounting to less than 2% of cells are not WNT tumors (d). Lack of cytoplasmic β-catenin immunoreactivity is exceptional in medulloblastomas, but clusters of dense neurocytic cells in classic tumors are notably immunonegative (e). Desmoplastic medulloblastomas characteristically show enhanced cytoplasmic β-catenin immunoreactivity within nodules (f)

Fig. 3

Filamin A immunoreactivity. Cytoplasmic immunoreactivity for filamin A is present across this classic medulloblastoma (a). As for GAB1, filamin A staining in desmoplastic SHH tumors tends to be internodular in MBENs (b), but in both nodules and internodular regions in paucinodular tumors (c). Non-SHH/WNT tumors are immunonegative for filamin A, apart from blood vessels and rare reactive astrocytes, which provide an internal control for the method (d)

Fig. 4

YAP1 immunoreactivity. Nuclear (predominantly) and cytoplasmic YAP1 immunoreactivity are evident in the SHH anaplastic medulloblastoma (a). This D/N medulloblastoma shows strong YAP1 staining in internodular tumor cells and scattered intranodular cells (b). This MBEN shows only internodular YAP1 immunoreactivity (c). Paucinodular tumors show only weak nodular staining for YAP1 (d). The sole classic WNT medulloblastoma that contained dense foci of neurocytic cells (the rest were non-SHH/WNT) showed no YAP1 reactivity in these foci, but staining in surrounding tumor cells (e). Non-SHH/WNT tumors are YAP1-immunonegative, but the vasculature is immunopositive, providing an internal control for the method (f)

Fig. 5

Clinical, pathological, and cytogenetic features of tumor cohort by molecular subgroup. Pathological variant: brown LC/A, light yellow D/N, white classic. Age group: brown adult, dark yellow infant, white child. Chromosome 6: light yellow monosomy, white not monosomy. PTCH1 locus: brown 9q22 loss, white no 9q22 loss. Chromosome 17: Dark yellow i(17q), light yellow other chromosomal imbalance, white no chromosomal imbalance. MYCN: brown amplified, white not amplified. MYC: dark yellow amplified, white not amplified. Metastatic disease at presentation: brown yes, white no. Sex: dark yellow female, white male. Green result not available

Fig. 6

Medulloblastoma pathological variants and molecular subgroups: age at diagnosis. The cumulative proportion of five histopathological medulloblastoma variants is plotted against age at diagnosis: blue classic, black MBEN, red LC/A, green D/N, orange non-desmoplastic nodular (a). The frequency (%) of three histopathological variants of medulloblastoma (blue classic, red LC/A, green desmoplastic) is plotted against ten age groups from birth to adulthood (b). The cumulative proportion of three molecular subgroups is plotted against age at diagnosis: blue SHH, green WNT, red non-SHH/WNT (c). The frequency (%) of three molecular subgroups of medulloblastoma (blue SHH, green WNT, red non-SHH/WNT) is plotted against ten age groups from birth to adulthood (d)

Fig. 7

Outcome analyses among patients aged 3–16 years on the CNS9102/PNET3 trial. Progression-free survival curves split by three histopathological variants of medulloblastoma: green D/N, blue classic, red LC/A (aP = 0.009). PFS curves split by three molecular subgroups of medulloblastoma: green WNT, blue SHH, red non-SHH/WNT (bP = 0.02). PFS curves split into five groups on the basis of molecular subgroup and pathological variant: green WNT, blue SHH classic or D/N, orange non-SHH/WNT classic or D/N, black SHH LC/A, red non-SHH/WNT LC/A (cP = 0.0003). PFS curves split into five groups on the basis of molecular subgroup and clinicopathological risk (standard-risk: tumors without metastasis, LC/A phenotype, or MYC amplification, high-risk: tumors with metastatic disease, LC/A phenotype, or MYC amplification): green WNT, blue SHH standard-risk, orange non-SHH/WNT standard-risk, black SHH high-risk, red non-SHH/WNT high-risk (dP < 0.0001)