Objective: To assess the prevalence of microsatellite instability in a series of endometrial carcinomas as well as to define the clinicopathologic features and estrogen receptor (ER) and progesterone receptor (PR) status associated with microsatellite instability (MI).
Methods: We examined 40 cases for replication error (RER) using polymerase chain reaction, polyacrylamide gel electrophoresis and silver stain at 8 microsatellite loci. Immunohistochemical staining of 27 paraffin sections was performed using antibodies to ER and PR. Finally, MI was compared with the clinicopathologic characteristics as well as ER and PR status.
Results: MI was observed in 9 (23%) at two or more loci, which is defined as RER positive phenotype. The 9 RER positive cases were all endometrioid type. Four non-endometrioid tumors failed to show MI in any locus. RER positive phenotype was more frequent in poorly differentiated (50%) than in well differentiated tumors (15%). We found no significant correlation of RER with stage and depth of invasion. Of 27 carcinomas, 19 (70%) showed homogeneous positive staining for ER and PR. ER and PR positive staining occured more frequently in RER negative endometrioid cancers than in RER positive cases.
Conclusions: MI is one of the molecular mechanisms of a subset of endometrial carcinomas. Its frequency is associated with tumor grade, histological type and ER or PR status.