Mixed Oligoastrocytoma (MOA)
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MOA is a tumor composed of a conspicuous mixture of two distinct cell types morphologically resembling the tumor cells in oligodendroglioma and LGG. MOA is a WHO Grade II glioma.
Because of the variability in criteria used to distinguish MAO from oligodendroglioma or LGG, it is difficult to estimate its incidence. Males appear to be slightly more affected (1.2:1).
Like oligodendrogliomas, MOA typically occurs in the cortex and white matter of the cerebral hemispheres, most commonly in the frontal lobe.
Patients with MOA present in a manner similar to patients with oligodendrogliomas or LGG.
MOA presents with radiographic features indistinguishable from those of an oligodendroglioma.
MOA is macroscopically indistinguishable from an oligodendroglioma, though its cellular heterogeneity may manifest as variations in tumor density and color.
The diagnosis of MOA requires the presence of both an oligodendroglial and astrocytic neoplastic component. These components may be biphasic or intermingled. Overally, MOAs have mildly to moderately increased cellularity, with no or low mitotic activity.
MOAs often display a biphasic pattern of genetic mutations common to oligodendrogliomas and LGGs.
Mean survival time following medical and surgical intervention is 6.3 years, with 5- and 10-year survival rates of 58% and 32%, respectively. Risk of malignant progression is thought to correspond to the astrocytic component of the tumor. Factors though to confer more favorable outcome include young age, chromosomes 1p and 19q deletion, frontal location, gross total surgical resection, and post-operative Karnofsky score.