p53 protein alterations in adult astrocytic tumors and oligodendrogliomas

p53 is a tumor suppressor gene implicated in the genesis of a variety of malignancies including brain tumors. Overexpression of the p53 protein is often used as a surrogate indicator of alterations in the p53 gene.

In this study, data is presented on p53 protein expression in adult cases (>15 years of age) of astrocytic (n=152) and oligodendroglial (n=28) tumors of all grades. Of the astrocytic tumors, 86% were supratentorial in location while remaining 14% were located infratentorially - 8 in the the cerebellum and 13 in the brainstem. All the oligodendrogliomas were supratentorial.

p53 protein expression was evaluated on formalin-fixed paraffin-embedded sections using streptavidin biotin immunoperoxidase technique after high temperature antigen retrieval.

Overall 52% of supratentorial astrocytic tumors showed p53 immunopositivity with no correlation to the histological grade. Thus, 58.8% of diffuse astrocytomas (WHO Grade II), 53.8% of anaplastic astrocytomas (WHO Grade III) and 50% of glioblastomas (WHO Grade IV) were p53 protein positive. In contrast, all the infratentorial tumors were p53 negative except for one brainstem glioblastoma. Similarly, pilocytic astrocytomas were uniformly p53 negative irrespective of the location. Among oligodendroglial tumors, the overall frequency of p53 immunopositivity was lower (only 28%), though a trend of positive correlation with the tumor grade was noted - 25% in Grade II and 31.5% in grade III (anaplastic oligodendroglioma). Interestingly, p53 labeling index (p53 LI) did not correlate with the histopathological grade in both astrocytic and oligodendroglial tumors.

Thus, this study gives an insight into the genetic and hence biological heterogeneity of gliomas, not only between astrocytic tumors vs. oligodendrogliomas but also within astrocytic tumors with regard to their grade and location. With p53 gene therapy trials in progress, this will possibly have future therapeutic implications.