Analysis of p53 mutation and expression in pleomorphic xanthoastrocytoma

Pleomorphic xanthoastrocytoma (PXA) is a rare, superficially situated tumor that most frequently occurs in the temporal lobe of young adults and is often associated with seizures. It generally has a relatively favorable prognosis. Prior studies have shown that TP53 mutations may occur in up to 25% of PXAs, suggesting that PXA may have an etiology similar to diffuse astrocytoma rather than pilocytic astrocytoma. In the present study, we performed immunostaining for p53 protein and examined the mutation status of exons 5-8 of the p53 gene in 55 PXAs, 8 of which had undergone one or multiple recurrences. Of 55 primary PXAs, 35 (64%) showed staining in <1% of tumor cells, 15 (27%) in 1-10%, 4 (7%) in 11-50%, and only 1 (2%) in >50%. No significant increase in p53 protein expression was noted in recurrences, even when associated with increased histological anaplasia. We found a TP53 heterozygous mutation in exon 7 in 1 of 47 primary tumors that yielded useable DNA, and in its recurrence 3 years later. This tumor, a grade II PXA, did not show signs of anaplastic transformation at recurrence. Eleven additional recurrences from 7 patients, 5 of which showed signs of histological anaplasia, did not show TP53 mutations in exons 5-8. Based on our data, the p53 mutation appears to be an uncommon (2%) genetic event in PXA formation and does not appear to be involved in tumor progression. Consequently, our findings suggest that the genetic events that underlie PXA formation differ from those involved in diffuse astrocytoma.