Abstract: Objective To investigate the clinicopathologic features and clinical significance in mismatch repair (MMR) of deficient endometrial carcinoma. Methods A total of 108 endometrial carcinoma cases younger than 50 years of age who were underwent routine laparotomy in our hospital were included in this study. Immunohistochemistry staining was used for 4 MMR proteins (MLH1, MSH2, MSH6 and PMS2). Patients were divided into two groups (MMR deficiency group and MMR normal group) based on the results of immunohistochemistry staining. Results Thirty-three percent of cases (36 patients) showed at least one deletion of MMR protein expression. The clinicopathological features of 36 cases with deletion of MMR protein expression were analyzed. The 31% showed deep myometrium invasion and 25% were with intense lymphocyte infiltration around tumor cells. Thirty-five percent of endometrial carcinomas associated with mucinous, clear cell or other differentiations, and 14% with heterogeneity. Background endometrium of majority of the cases displayed proliferative endometrium. There were 20% cases complicated with ovarian carcinoma. Features included deep myometrium invasion, lymphocyte infiltration around tumor cells, multiple differentiations and complicated with ovarian carcinoma. There were significant differences in background endometrium between endometrial carcinoma combined with ovarian cancer group and control group. Conclusion MMR deficient endometrial carcinoma has characteristic features, which are different from both type I and type II endometrial carcinoma.

Key words: endometrial neoplasms, genes, colorectal neoplasms, hereditary nonpolypopsis, immunohistochemistry, MMR gene, Lynch syndrome