Prognostic relevance of p53 protein expression in glioblastoma

TP53 plays a key role in cellular response to DNA-damaging agents, and mutation of this gene, which is associated with immunohistochemically detectable p53 protein accumulation, may influence response to chemo- and radiotherapy. We investigated immunohistochemically the influence of p53 protein accumulation in 114 consecutive cases of primary glioblastoma treated by surgery and adjuvant radio- and chemotherapy. In addition, we determined cellular proliferation index using the antibody MIB-1 and apoptotic index of tumor cells using the TUNEL-assay. Twenty-nine patients (25.4%) were considered as positive with regard to p53 protein expression (>50% p53 immunostained tumor cells). Patients with p53 positive glioblastomas were significantly younger (mean age 54.4+/-2 years) than those with p53 negative tumors (mean age 61.4+/-1.1 years) (p=0.002, Mann-Whitney test). While no significant difference in apoptotic index was found, we observed a significantly higher MIB-1 labeling index (LI) in patients with p53 positive tumors (median LI: 36.4%) compared to p53 negative ones (median LI: 23.8%) (p=0.005, Mann-Whitney test). p53 protein expression was associated with significantly longer survival in univariate analysis (p=0.0399, log-rank test). In multivariate analysis of overall survival (Cox regression) only postoperative Karnofsky performance status remained as independent prognostic factor. We conclude that glioblastoma patients with immunohistochemically detectable p53 protein expression, who received adjuvant radio- and chemotherapy, have a significantly better overall survival, possibly due to increased sensitivity to this adjuvant treatment.