Introduction: P53 is a tumor suppressor gene that helps regulate the cell cycle. The gene is involved in DNA repair and programmed cell death. Mutations of this gene are often associated with various cancers. The importance of p53 mutational status remains controversial in regards to prognosis for Glioblastoma (GBM). Nevertheless, some studies suggest that p53 mutation carries a worse prognosis. Laboratories frequently employ immunohistochemistry (antibody clone (DO-7)) to determine p53 positivity. Many use a 10% nuclear staining threshold to imply p53 mutation positivity. We question whether this form of assay is sensitive and specific enough in the determination of this potentially important mutation.
Methods: Standard laboratory results on p53 immunohistochemical staining were obtained on 34 glioblastoma tissue samples. We utilized Sanger gene sequencing methodology to determine actual p53 mutations within the same samples. We compared reported laboratory-derived percent nuclear antibody staining with actual gene sequencing-determined mutations.
Results: Out of our 34 histologically confirmed GBM samples, 21 were deemed “positive” for p53 mutation via laboratory immunohistochemistry. That is, they were found to have greater than 10% of their nuclei staining positive, implying that 62% of the tumors had p53 mutations. Utilizing gene sequencing, we identified only six with actual p53 mutations (18%). In the samples with actual p53 mutations, nuclear antibody staining was on the order of 75% (average).
Conclusions: Our study suggests that a 10% threshold for nuclear staining in immunohistochemical assays for p53 mutation is too low, and will result in a high rate of false positivity. We would suggest a much higher threshold. More to the point, we believe that gene sequencing should be the principal method employed in determining p53 mutational status.
Patient Care: More accurate determination of p53 may have a significant impact on determining prognosis in GBM patients.
Learning Objectives: to understand that antibody staining for p53 mutation in glioblastoma may have high rates of false positive.
to understand that gene sequencing is a preferred method for determining p53 mutational positivity
p53 may correlate with bad prognosis in gbm