HG-07: DETECTION OF K27M MUTANT PEDIATRIC GLIOBLASTOMAS BY IMMUNOHISTOCHEMISTRY

Pediatric glioblastomas (GBM) are lethal and fatal tumors and ∼30% of GBM and ∼80% of diffuse intrinsic pontine gliomas show K27M mutations in the H3F3A gene, a variant encoding histone H3.3. These mutations lead to global reduction in H3K27me3. Our goal was to develop biomarkers for the histopathologic detection of these tumors. Therefore, we evaluated the utility of measuring H3K27me3 global reduction as a biomarker and tested an antibody directed specifically against the K27M mutation in 290 samples of 203 pediatric (including 38 pediatric high-grade astrocytomas), 38 adult brain tumors of various subtypes and grades and 49 non-neoplastic reactive brain tissues. Detection of K27M by immunohistochemistry showed 100% sensitivity and specificity and was superior to reduction in H3K27me3 as a biomarker. Moreover, cases that stained positive for K27M showed a significantly poor prognosis compared to corresponding negative tumors. These results suggest that immunohistochemical detection of K27M is a sensitive and specific surrogate for K27M mutations and a prognostic marker.