Reverse correlation between P-glycoprotein expression and proliferative activity in endometrial adenocarcinoma

Immunohistochemical study was employed using a monoclonal antibody (C219) to investigate P-glycoprotein expression in 23 normal endometria and 40 endometrial adenocarcinomas. P-glycoprotein immunopositivity was observed in the mid- to late-proliferative phase and the whole secretory phase of normal endometrium. In contrast, no P-glycoprotein was detected in endometrium of early proliferative phase nor post-menopausal endometrium. We also investigated the expression of P-glycoprotein in endometrial cancers to find 16 out of the 40 endometrial adenocarcinomas (40%) expressed P-glycoprotein. P-glycoprotein immunopositivity was often observed in gland growing parts but not in solid growing parts in a given tumor specimen. Proliferative activity of the tumor, as measured by PCNA labeling, was significantly higher in the P-glycoprotein-negative group than that in P-glycoprotein-positive group (P < 0.005). Thus, there was a strong reverse relation between P-glycoprotein expression and proliferative activity in endometrial adenocarcinomas.