The presence of p53 protein in non-neoplastic pleural mesothelium (40 cases) and in human malignant mesothelioma (36 cases) was assessed immunohistochemically using the antibodies DO7, CM-1, and PAb240. In a quarter of the malignant mesotheliomas, there was nuclear immunoreactivity for p53 protein with both the DO7 and CM-1 antibodies. There were no statistically significant differences between the various mesothelioma subtypes (P > 0.05). No immunoreactivity was found with the PAb240 antibody, suggesting absence of mutant-type p53 protein. Nonneoplastic mesothelium was not immunoreactive with any of the antibodies. We conclude that there is immunoreactivity for p53 protein in some mesotheliomas. p53 protein immunoreactivity could be used to discriminate between neoplastic and reactive mesothelium.

Immunohistochemical staining of 36 malignant mesotheliomas and 45 cases of non-neoplastic mesothelium including 20 specimens with signs of hyperplasia were investigated using murine monoclonal antibodies directed against p21 ras protein, Ha-ras protein, K-ras protein, and N-ras protein. All cases of non-neoplastic mesothelium and the majority of the malignant mesotheliomas (78 per cent) showed cytoplasmic and often submembranous immunoreactivity in more than 50 per cent of the cells with both the pan-ras and N-ras antibody. No immunoreactivity was observed for Ha- and K-ras. There was no statistically significant difference with respect to immunoreactivity between neoplastic and non-neoplastic mesothelium or between the various mesothelioma subtypes.