Histone H3 K27M mutations in adult cerebellar high-grade gliomas

Adult cerebellar high-grade gliomas (HGG) are rare and their molecular basis has not been fully elucidated. Although a diffuse midline glioma H3 K27M-mutant, a recently characterized variant of HGG, was reported to occasionally occur in the cerebellum, adult cases were rarely tested for this mutation; only five mutant cases have been reported to date. It currently remains unknown whether H3 K27M-mutant cerebellar gliomas share common histological features or have a uniformly dismal prognosis. In the present study, we assessed the prevalence of histone H3 K27M mutations in ten adult cerebellar HGG, identifying two H3F3A-mutant cases. One case was a 70-year-old female with a cystic lesion. Histologically, the tumor was considered to be glioblastoma; however, a part of the tumor exhibiting low proliferative activity appeared to be consistent with long-standing H3 K27M-mutant tumors in the literature. Another case was a 69-year-old male. The tumor showed a distinct circumscribed histology with minimal astrocytic differentiation, suggesting a nosological issue in the diagnosis of diffuse midline glioma. More cerebellar tumors need to be tested for H3 K27M mutations to clarify the clinical and histopathological spectra of this tumor.