INTEROBSERVER VARIATION OF P53 IMMUNOHISTOCHEMISTRY - AN ASSESSMENT OF A PRACTICAL PROBLEM AND COMPARISON WITH OTHER STUDIES

The aims of this study were to analyse the expression of p53 by immuno histochemistry in a range of malignant and pre-malignant conditions an d to assess the degree of inter-observer variability in interpretation of p53 immunostaining. Formalin-fixed paraffin-embedded sections from 28 colorectal carcinomas (CRC), 40 cervical intraepithelial neoplasia lesions (GIN), 22 transitional cell carcinomas of the bladder (TCC), 10 invasive squamous carcinomas of uterine cervix and 21 squamous cell carcinomas of skin were examined. A polyclonal antibody was used in 9 0 cases. A monoclonal antibody was used in the remainder. Ten cases we re stained with both. Aberrant expression of p53 protein was documente d in 48% of squamous cell carcinomas of skin, 29% of CRC, 22% of CIN a nd 23% of TCC. All cases of squamous cell carcinoma of uterine cervix were negative. Inter- observer variation occurred in 7% of cases exami ned. This was confined to two tumour groups, TCC and CIM Our results s howed that p53 oncoprotein expression by immunohistochemistry was iden tified in 26% of cases but the range was wide (0-48%) and appeared to be tumour specific. Inter-observer variability in the interpretation o f immunohistochemical staining was low (7%) and was restricted to two tumour groups.