Prognostic relevance of TP53 mutations, p53 protein, Ki-67 index and conventional histological grading in oligodendrogliomas.

The prognostic value of tumour grading according to WHO, Ki-67 proliferation index, p53 labelling index and TP53 gene mutations was assessed in 59 patients (33 oligodendrogliomas WHO grade II, 15 anaplastic oligodendrogliomas, 11 glioblastomas with oligodendroglial growth pattern). The minimal observation period was 5 years after operation. According to multivariate correlation and regression tree (CART) analysis grading was the prime prognostic factor (grade II vs. anaplastic tumours, p < 0.00001). Grade II oligodendrogliomas were further divided into tumours with and without TP53 mutations (p < 0.05) whereas anaplastic tumours were subdivided according to age (p < 0.05, cut off at 57 years) and p53 protein accumulation (p < 0.05, cut off at 2%, age 57 years). Ki-67 labelling index correlated highly significantly with grading but had no independent prognostic relevance in CART analysis. Accumulation of wild-type p53 protein was not related to bcl-2 expression, a co-expression of p53 and bcl-2 was found at similar frequencies in tumours with or without TP53 mutations (4/12 vs. 3/11). Since accumulation of wild-type and mutant p53 are both associated with a poor prognosis, it is suggested to include immunohistochemical evaluation of p53 protein in routine diagnostics of oligodendrogliomas.