P53 protein immunohistochemical expression in colonic adenomas with and without associated carcinoma

P53 protein immunohistochemical (IHC) expression was investigated in a series of colonic adenomas and carcinomas to determine the p53 immunohistochemical expression of adenomas in general compared with carcinomas, the difference in staining pattern between adenomas with associated carcinoma and those without associated carcinoma, and the difference in p53 staining in the usual adenomas (low-grade dysplasia) compared with those harboring high-grade dysplasia.

The study involved a series of 20 adenomas without concurrent carcinoma (group 1 adenoma), 29 adenomas with concurrent carcinoma (group 2 adenoma), and 20 carcinomas. Sections of the paraffin-embedded tissues were stained with DO-7 p53 monoclonal antibody after microwave antigen-retrieval method. Cases with nuclear staining in > or = 20% of the tumor cells were considered positive.

Analysis of results showed that 65% of carcinomas and 37% of all adenomas were reactive with p53 IHC staining (p = 0.03). With respect to the adenomas, 30% of group 1 and 41% of group 2 adenomas were reactive for p53 protein (p = 0.42).

Our data demonstrate a statistically significant higher p53 expression rate in colonic carcinomas than in adenomas, and that adenomas with concurrent carcinomas are more frequently p53 positive than those without concurrent carcinoma, but this was not statistically significant. Also, p53 expression is more frequent and intense in adenomas with high-grade dysplasia (10/20, 50%) than in ordinary adenomas with low-grade dysplasia (8/29, 28%), which suggests a strong correlation between the degree of dysplasia in colonic neoplasia and p53 expression pattern.