Immunophenotype of pleomorphic xanthoastrocytoma.

Pleomorphic xanthoastrocytoma (PXA) is an uncommon tumor, often seizure-associated and occurring in the temporal lobe of young adults. Although its cells are considered astrocytic in nature, recent studies suggest the presence of neuronal differentiation and a possible relationship to glioneuronal neoplasms. We immunostained 40 cases of PXA, including two composite PXA-gangliogliomas (PXA-GG), with a panel of glial (glial fibrillary acidic protein, S-100 protein) and neuronal markers (class III beta-tubulin, synaptophysin, neurofilament proteins, MAP2, and chromogranin A). Conventional PXAs demonstrated immunoreactivity for glial fibrillary acidic protein (100% of cases), S-100 protein (100%), class III beta-tubulin (73%), synaptophysin (38%), NF proteins (18 and 8%), and MAP2 (8%). Chromogranin A stain was absent in all conventional PXA cases. Neoplastic ganglion cells in both PXA-GGs stained with class III beta-tubulin, synaptophysin, and chromogranin A. Ultrastructural studies, performed in nine cases, demonstrated neuronal features including microtubules, dense core granules, and/or clear vesicles largely limited to cell processes (two PXAs) and in the cytoplasm (PXA component of one PXA-GG). Although the essential nature of PXA is clearly and uniformly glial, the significance of the limited neuronal differentiation is unclear, as it is the relationship between conventional PXA and PXA-GG. We found no evidence that the former is a precursor of the latter.