Cyclical change of hMSH2 protein expression in normal endometrium during the menstrual cycle and its overexpression in endometrial hyperplasia and sporadic endometrial carcinoma

BACKGROUND. The role of hMSH2 protein, one of the major DNA repair proteins, until now, had not been elucidated in terms of normal endometrial function during the menstrual cycle. The current study was designed to address this issue and to determine whether the expression of hMSH2 is altered in the course of endometrial carcinogenesis. METHODS. Immunohistochemical reactivity with a monoclonal antibody against the hMSH2 protein was examined in endometrial tissue specimens from 45 patients with normal endometrium, 51 patients with endometrial hyperplasia, and 27 patients with endometrial carcinoma. Immunohistochemical expression of proliferating cell nuclear antigen (PCNA) also was studied in the same samples as a measure of the proliferative activity and was compared with hMSH2 expression in each sample. RESULTS. The functional layer of normal endometrium displayed cyclic changes in hMSH2 protein expression during the menstrual cycle, showing positive expression in the proliferative phase and becoming weak to negative in the secretory phase. This expression pattern was similar to that of PCNA. Sixty-three percent of endometrial carcinomas showed strong positivity for both hMSH2 and PCNA expression, and 7.4% had an intensity of hMSH2 protein expression similar to that found in normal proliferative endometrial glandular cells. There was only I sample (3.7%) that was completely negative for hMSH2 expression, and 26% of samples were weakly positive for PCNA and hMSH2 protein. All simple hyperplasias and the majority of complex and atypical hyperplasias showed positive immunoreactivity for hMSH2 and PCNA. CONCLUSIONS. This study demonstrates that hMSH2 protein expression changes during the menstrual cycle in parallel with proliferative activity. In most patients with sporadic endometrial carcinoma, the expression of hMSH2 protein is consistent with PCNA expression. In contrast, loss of hMSH2 expression is observed rarely in patients with sporadic endometrial carcinoma. (C) 2002 American Cancer Society.