Strongly reduced expression of the cell cycle inhibitor p27 in endometrialneoplasia

In the present study we investigated the expression of the cell cycle inhib itor p27 in endometrial neoplasia using immunohistochemistry with a p27-spe cific antibody. Expression of p27 in endometrial carcinomas was compared wi th expression in the normal endometrium throughout the cycle. Normal endome trial cells showed strong nuclear expression of p27. Expression was present throughout the cycle and was stronger during the secretory phase. We found strongly reduced or abolished expression of p27 in endometrial carcinoma ( 85.3% of cases). The 41 tumours analysed were classified according to p27 s taining intensity and percentage of positive cells into the following categ ories of p27 expression: negative/very low (56.0%); low (29.3%); moderate ( 14.7%) and high (0.0%). All the p27-positive tumours were well-differentiat ed endometrioid carcinomas of malignancy grade G1. Comparison with the p53 status showed that all tumours with strong p53 expression had low/negative p27 staining, while those that were positive for p27 had negative/low p53 s taining. Reduced or absent p27 levels were also observed by Western blot an alysis both in tumour samples and in HEC-1B endometrial adenocarcinoma cell s. It thus seems that p27 expression is essential for the control of normal endometrial proliferation, and reduced or absent p27 expression may be an important step in endometrial carcinogenesis.