Microsatellite instability in endometrioid type endometrial adenocarcinoma is associated with poor prognostic indicators.

Microsatellite instability (MSI) has been reported in 25% to 45% of sporadic endometrial carcinoma. The clinicopathologic and molecular characteristics of MSI-high phenotype in colorectal and gastric carcinomas have been widely investigated; however, the clinicopathologic impact of MSI on endometrial carcinomas remained unclear. This study was performed to determine the clinicopathologic and molecular significance of MSI in endometrial carcinomas. We analyzed the MSI status using National Cancer Institute-recommended 5 microsatellite markers, and the immunohistochemical profiles of various regulatory proteins of cell cycle and apoptosis using tissue microarray in 100 endometrial carcinomas. The results were compared between MSI-high and MSI(-) groups as for the traditional clinicopathologic prognostic parameters and the immunoreactivities of various regulatory proteins. We especially focused on the endometrioid type adenocarcinoma to exclude the bias from nonendometrioid type adenocarcinomas with more aggressiveness and a close association with MSI(-) phenotype. The incidence of MSI-high phenotype was significantly higher in endometrioid type than in nonendometrioid serous type (20% vs. 0%, P<0.001). It showed orderly increase in the frequencies of MSI-high phenotype in higher histologic grade (13% vs. 21% vs. 50% in histologic grade I, II, and III, P=0.039). The MSI-high phenotype was related with the presence of lymphovascular invasion (P=0.008), deep myometrial invasion (P=0.040), and the higher clinical stages (P=0.018) independent of tumor grade. We also found a correlation between MSI-high phenotype and higher cyclin A and skp2 immunoreactivity (P=0.03 and 0.05, respectively), known to be the poor prognostic molecular indicators. According to these results, the MSI may represent the poor prognostic impact on the endometrioid type endometrial adenocarcinoma.