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.
The MIB-1 labelling index and the frequency and intensity of p53 staining in both the pilocytic astrocytoma and the astrocytoma group were significantly lower than in the anaplastic astrocytoma plus glioblastoma group (P < 0.001).
All primary tumors were histologically diagnosed as pilocytic astrocytoma (WHO grade I), except for one anaplastic pilocytic astrocytoma (WHO grade III) which developed in an NF1 patient and recurred as glioblastoma multiforme (WHO grade IV). p53 mutations were detected using an assay in yeast which tests the transcriptional activity of p53 proteins synthesized from tumor mRNA-derived p53-cDNA templates.