Routinely assessed morphological features correlate with microsatellite instability status in endometrial cancer

Microsatellite instability (MSI) has been shown to be important in the molecular pathogenesis of both sporadic and inherited endometrial carcinomas of endometrioid type. It is likely prognostically significant as well. The aim of this study was to determine whether MSI phenotype in endometrial carcinoma was associated with specific morphologic patterns and therefore predictable by tumor morphology. The study subjects consisted of 102 patients with nearly equal representation of MSI high (MSI-H; n = 52) and non-MSI-H (n = 50) endometrial tumors. Microsatellite instability was determined by the standard polymerase chain reaction method using the National Cancer Institute-recommended set of 5 markers. The MSI-H and non-MSI-H groups were matched for patient age, race, histologic type (all endometrioid), International Federation of Gynecology and Obstetrics grade, and disease stage. Assessed morphological features included host inflammatory response (tumor infiltrating lymphocytes [TILs], peritumoral lymphocytes, peritumoral lymphoid follicles, and neutrophilic infiltration), tumor characteristics (cytologic grade, growth pattern, tumor heterogeneity, invasion pattern, metaplastic changes, necrosis, and lymphovascular invasion), and background endometrium (hyperplasia, atrophy, and polyp). Of all the features examined, TIL counts and peritumoral lymphocytes correlated significantly with MSI-H status. Their statistical relationship was strengthened in the presence of a nonpapillary growth pattern and endometrial hyperplasia. On multivariate analysis, TIL counts and peritumoral lymphocytes remained independent predictors for MSI-H status. At a cutoff point of 40 TILs/10 high power fields, TIL counts had a sensitivity of 85% in predicting MSI status in endometrioid endometrial carcinoma, with a specificity of 46%. This specificity increased as higher cutoff points were selected, but sensitivity decreased. Given that analogous features have been encountered in MSI-H colorectal cancers, our findings suggest a similar relationship between tumor phenotype and DNA mismatch repair abnormalities in both endometrial and colorectal tumors. Therefore, morphological patterns encountered in endometrial carcinoma may prove useful in screening tumors under consideration for MSI testing and identifying appropriate patients for referral to a genetic counseling service.