BAT-26 microsatellite instability does not correlate with the loss of hMLH1 and hMSH2 protein expression in sporadic endometrial cancers

Abstract

Microsatellite instability (MSI) is detected in about 20-25% of endometrial cancers (ECs). Incidence of this alteration correlates with lack of expression of certain mismatch repair genes such as hMLH1 and hMSH2. Although assessment of several markers has been proposed for identification of microsatellite unstable tumours, BAT-26, a mononucleotide microsatellite repeat, has been shown to be highly efficient when used as a single marker. The aim of the study was to evaluate instability within BAT-26 and expression of hMLH1 and hMSH2 proteins in sporadic endometrial cancer as well as to correlate these findings with histopathologic and clinical characteristics of tumours. Samples of 88 (74 endometrioid and 14 non-endometrioid) ECs were investigated for instability within BAT-26 by means of PCR and expression of hMLH1 and hMSH2 proteins using immunohistochemistry. BAT-26 MIS was discovered in 23.9% of endometrial cancers. Incidence of MSI did not correlated with grade, stage or depth of invasion. BAT-26 MSI was more frequent in non-endometrioid compared to endometrioid tumours (35.7% vs. 21.6%, respectively), but the difference was not statistically significant. Lack of hMLH1 and hMSH2 protein expression was detected in 21.6 and 15.9% of ECs, respectively, and did not correlate with clinicopathologic features of tumours. Loss of both hMLH1 and hMSH2 protein expression was similar in BAT-26 stable and unstable cancers. All cases of non-endometrioid tumours with BAT-26 MSI were positive for hMLH1. We can conclude that BAT-26 used alone may not be a reliable marker for identification of sporadic ECs with microsatellite instability induced by deficient expression of hMLH1 and hMSH2.