IDH1 and oligodendroglioma: Our study revealed that loss of H3K27me3 nuclear staining among 1p/19q codeleted oligodendrogliomas is frequent in cases harboring IDH1-R132H mutation. We consider that H3K27me3 immunoreactivity could predict the 1p/19q codeletion status along with IDH1-R132H and ATRX immunostaining.