Microsatellite instability in endometrial cancer: relation to histological subtypes.

Fifty-one endometrial cancers were analyzed with regard to whether or how microsatellite instability (MI) was associated with the development of different types of endometrial malignant neoplasms. We investigated 6 loci previously reported as informative for colorectal cancer and a group of 8 loci located on 6q. Replication error (RER+) phenotype was detected in 10 of 51 (19.6%) endometrial cancers (ECs), all but one of which showed endometrioid differentiation. On the contrary, the RER+ phenotype was not detected in serous carcinomas and malignant mixed Müllerian tumors. MI was present in both early and advanced stage ECs. No correlation was found between age, grade, stage, familial pattern, mitotic index, and the RER+ phenotype of ECs. Only 1 of 8 endometrial carcinomas showing MI was associated with mutant p53 expression, while the majority of RER+ tumors were positive for estrogen and progesterone receptors. Our findings suggest that MI plays an early role in endometrial tumorigenesis and is significantly correlated with adenocarcinomas showing endometrioid features (EAs). The frequent involvement of the telomeric region of chromosome 6 in the MI of EA is an indication that this region may be crucial in the process of EA tumorigenesis.