Abstract
Since the molecular-based classification of gliomas has been a trend in recent years, pathological diagnoses are required to balance that trend. In oligodendrogliomas, the combination of a classic morphology with positive mutant IDH1 and negative p53 findings on immunohistochemistry is highly correlated with the genetic signature of the 1p/19q co-deletion and IDH mutation. Oligodendrogliomas with a non-classic histology often lack this genetic signature. Oligoastrocytomas exhibit a non-classic histology, even if they have the co-deletion, suggesting that they may be distinct from classic oligodendrogliomas. In high-grade gliomas, the identification of an oligodendroglioma component is controversial, as these lesions always display non-classic features. For patients with such lesions, genetic testing is mandatory. Non-deleted, non-classicoligodendrogliomas are, however, not always astrocytomas, and an effort to identify novel genetic markers is required. The future classification of gliomas should take into account both phenotypes and genotypes; however, it is premature to switch from a morphologic diagnosis to genetic testing, as the latter is not universally available. This review summarizes the current knowledge of pathological features of oligodendroglioma.
