Microsatellite instability and hMLH1/hMSH2 expression in barrett esophagus-associated adenocarcinoma

BACKGROUND. Microsatellite instability (MST) has been documented in malignancies associated with hereditary nonpolyposis colon carcinoma and in sporadic malignancies of the colon, stomach, and endometrium. In these malignancies, MST is associated with defects in the DNA mismatch repair enzymes hMSH2 and hMLH1. Defects in these enzymes result in a phenotype characterized by instability of multiple microsatellite repeat sequences throughout the genome. This study sought to determine the prevalence of MST in 80 primary Barrett esophagus-associated adenocarcinomas (BEAd) and to examine the relation of MST with the clinical and pathologic features of the tumors. METHODS. Eighty BEAd were evaluated for the presence of MST by using the microsatellite markers BAT25, BAT26, D10S219, D10S541, and D10S551. These tumors also were evaluated for immunohistochemical expression of hMSH2 and hMLH1. RESULTS. High levels of MST were not found in any of the tumors examined. Furthermore, immunohistochemical expression of hMSH2 and hMLH1 was retained in all cases evaluated. Evidence of low level MSI was found in 16% of tumors. In none of these tumors, however, was MST present in more than two of five loci. The presence of MST did not correlate with patient age, tumor stage, degree of differentiation, or with patient survival. CONCLUSIONS. High level MST and loss of hMLH1/hMSH2 expression is uncommon in BEAd. A subset of BEAd demonstrate low level MST. The presence of low level MST was not associated with the clinicopathologic features of the tumors examined.