Mixed glioma with molecular features of composite oligodendroglioma and astrocytoma: a true “oligoastrocytoma”?

Excerpt

The current World Health Organization (WHO) classification system designates oligoastrocytoma as a diffusely infiltrating glial neoplasm exhibiting morphological features of both astrocytoma and oligodendroglioma [4]. Perhaps not surprisingly, a broad spectrum of diffuse gliomas having varying proportions of oligodendroglial and astrocytic character falls into this diagnostic category, with the classification of each tumor as astrocytoma, oligodendroglioma, or oligoastrocytoma suffering from significant inter-observer variability [9]. Recent large-scale molecular profiling efforts [1‐3, 10] have emphatically confirmed earlier work [6] indicating that the vast majority of oligoastrocytomas, in addition to harboring mutations in IDH1/2, exhibit the signature genomic abnormalities of either pure oligodendroglioma (1p/19q codeletion, CIC and FUBP1 mutations) or astrocytoma (ATRX mutation, TP53 mutation) with almost complete mutual exclusivity. Moreover, studies to date, including a recent correlative investigation of 43 oligoastrocytomas [8], have failed to demonstrate distinct molecular abnormalities characterizing the astrocytic and oligodendroglial components of individual tumors. From a molecular standpoint then, oligoastrocytomas, as a group, seem to largely consist of tumors having either astrocytoma or oligodendroglioma signatures, and questions have been raised as to whether the diagnosis of oligoastrocytoma itself should be jettisoned from future WHO classification schemes [5]. …