P53 overexpression and proliferative potential in malignant meningiomas.
Meningiomas are generally benign, but some meningiomas show malignancy with invasion and high recurrence rates. We investigated whether alterations in p53 protein may contribute to malignant progression in meningiomas. Immunostaining for p53 protein was performed on paraffin and frozen sections from 61 patients with different grades of meningiomas using monoclonal antibodies (mAbs) DO-1 and pAb240. Immunoblot analysis was performed to quantitate the amount of p53 protein. Mutations in p53 genes were assessed by single-strand conformational polymorphism (SSCP) analysis. MIB-1 immunostaining was used to detect proliferative potentials of meningiomas. We found an overexpression of p53 protein in all of five cases of anaplastic meningiomas by immunohistochemistry using DO-1 mAb. No p53 positive cells were recognized in atypical meningiomas, and several cells were weakly stained in only two of 52 benign meningiomas. p53 staining index and immunoblot analysis indicated increasing amounts of p53 protein associated with subsequent recurrences of anaplastic meningiomas. The MIB-1 staining index was positively correlated with tumour grade and p53 protein overexpression. Immunostaining of frozen sections using the mutant-specific mAb pAb240, as well as mutation gene analysis by SSCP, indicate that the overexpressed p53 protein is not a mutant-but wild-type p53 protein. Four atypical meningiomas did not recur after surgical removal and radiation, while 4 anaplastic meningiomas with overexpressed p53 protein recurred repeatedly at short intervals even after radiation. Our results suggest that accumulation of p53 protein associated with highly proliferative potentials is a common and characteristic feature that may indicate malignant biological behaviour in meningiomas.