Microsatellite instability (MSI) due to replication errors occurs frequently in hereditary tumors. Association with functional inactivation of the mismatch repair (MMR) genes and lack of protein expression has been described. In endometrial carcinoma (EC), the prevalence and clinical significance of these phenomena are not well known. Therefore, DNA samples from 89 EC and 5 metachronous tumors were analyzed with polymerase chain reaction, using 5 microsatellite markers and a DNA sequencer for amplicon detection. The results were correlated with immunohistochemistry of hMLH1 and hMSH2. MSI at >or=2 loci (MSI-H) was detected in 10/89 EC (11%); 1 of 10 showed loss of both hMLH1 and hMSH2, and 5 of 10 showed loss of hMLH1 (P < 0.0001). MSI-H was observed frequently in tumors with mucinous differentiation (P = 0.048), >10% of solid-cribriform pattern (P = 0.037), International Federation of Obstetrics and Gynecology (FIGO) stage III to IV (4 of 13; P = 0.016), and necrosis >5% (P = 0.07). Loss of heterozygosity (LOH) in >or=1 loci was found in 17 of 156 (11%). Survival (Kaplan-Meier) was longer for patients with endometrioid tumors with predominant glandular pattern, <5% necrosis, low FIGO stage and grade, superficial myometrial infiltration, no lymph-vascular invasion (LVI), and loss of hMLH1 expression (all P <or= 0.04). Cox analysis showed independent value for stage, grade, histologic type and pattern, LVI, and hMLH1 expression (all P < 0.05). Age, MSI status, LOH, peritumoral inflammatory reaction, hMSH2, and development of metachronous tumors did not influence survival. In conclusion, MSI phenotype was observed in a small subset of mainly advanced-stage EC, frequently showing mucinous differentiation, areas of solid-cribriform pattern, and necrosis. It is often associated with loss of hMLH1 expression, which may be a prognostic marker, but only rarely with defects of hMSH2.
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