Microsatellite instability (MI), detected as electrophoretic shifts in
allele sizes of microsatellite DNA sequences, has been identified in
some colorectal carcinomas. Investigators have previously attributed s
uch microsatellite instability to replication errors (RER). The colore
ctal carcinomas with RER have been found to arise either sporadically
or in association with the hereditary non-polyposis colorectal cancer
(HNPCC) syndrome. Because endometrial carcinoma is also commonly assoc
iated with HNPCC, we studied 30 cases of endometrial carcinoma to char
acterize the presence of MI in these neoplasms. Seven cases (23%) show
ed MI. Four cases showed both Type I (large shifts) and Type II (small
shifts) mutation patterns and the remaining three cases showed Type I
mutations only. We conclude that MI frequently occurs in endometrial
cancers and that this type of genetic alteration may be an important p
athogenetic feature of this tumor type.