Prediction of a mismatch repair gene defect by microsatellite instability and immunohistochemical analysis in endometrial tumours from HNPCC patients

Abstract

Instability of microsatellite repeat sequences has been observed in colorectal carcinomas and in extracolonic malignancies, predominantly endometrial tumours, occurring in the context of hereditary non-polyposis colorectal cancer (HNPCC). Microsatellite instability (MSI) as a feature of human DNA mismatch repair (MMR)-driven tumourigenesis of the uterine mucosa has been studied primarily in sporadic tumours showing predominantly somatic hypermethylation of MLH1. The present study shows that all endometrial carcinomas (n=12) from carriers of MLH1 and MSH2 germline mutations demonstrate an MSI-high phenotype involving all types of repeat markers, while in endometrial carcinomas from MSH6 mutation carriers, only 36% (4 out of 11) demonstrate an MSI-high phenotype. Interestingly, an MSI-high phenotype was found in endometrial hyperplasias from MSH2 mutation carriers, in contrast to hyperplasias from MLH1 mutation carriers, which exhibited an MSI-stable phenotype. Instability of only mononucleotide repeat markers was found in both endometrial carcinomas and hyperplasias from MSH6 mutation carriers. In 29 out of 31 (94%) endometrial tumour foci, combined MSI and immunohistochemical analysis of MLH1, MSH2, and MSH6 could predict the identified germline mutation. The observation of MSI in endometrial hyperplasia and of altered protein staining for the MMR genes supports the idea that inactivation of MMR genes is an early event in endometrial tumourigenesis. A correlation was found between the variation in the extent and level of MSI and the age of onset of carcinoma, suggesting differences in the rate of tumour progression. A high frequency of MSI in hyperplasias, found only in MSH2 mutation carriers, might indicate a more rapid tumour progression, correlating with an earlier age of onset of carcinoma. The present study indicates that assessment of altered protein staining combined with MSI analysis of endometrial tumours might direct the mutational analysis of MMR genes.

High frequency of microsatellite instability and loss of mismatch‐repair protein expression in patients with double primary tumors of the endometrium and colorectum

“…Consistent with previous observations of loss of MSH6 expression in tumors from MSH2 mutation carriers, 34 we found a concomitant loss of MSH6 in all these tumors. Reduced staining for MSH2 has been observed previously in tumors from MSH6 mutation carriers, 34 as also seen in Patient 26, who had a germline MSH6 mutation.…”

“…8,12,33 However, MSI for only one mononucleotide marker has been demonstrated in endometrial tumors from MSH6 mutation carriers. 34 In our study, the immunohistochemical staining was retained for all three antibodies in all but one of the MSI-low tumors, suggesting that this lowgrade MSI is the result of alterations other than MMR gene mutations. In five patients, the two tumors investigated from each individual differed regarding MSI status, with one MSI-high tumor and one MSI-low or MSS tumor.…”

“…8,37 Although methylation of the MLH1 promoter in sporadic tumors is associated with abnormal immunohistochemical staining, some MLH1 mutations that cause HNPCC show normal immunohistochemical expression. 34,36,37 Accordingly, underlying MMR defects are not excluded in tumors with MSI and retained protein expression identified herein.…”

“…35 In HNPCC mutation carriers, it has been reported that a combined analysis with MSI and immunohistochemical staining for MLH1, MSH2, and MSH6 in the tumor tissue predicted a germline mutation in Ͼ 90% of patients. 34,35 MSI is seen in approximately 20% of sporadic endometrial and colorectal tumors, of which a large subset has abnormal MMR protein expression, most commonly affecting MLH1 with frequent hypermethylation of the MLH1 promoter. 8,9,13,14 Of the 67 tumors examined in the current study, 64 tumors were evaluated successfully for immunohistochemical expression of MLH1, MSH2, and MSH6.…”

Loss of ARID1A expression and its relationship with PI3K-Akt pathway alterations, TP53 and microsatellite instability in endometrial cancer

“…19,20 All tumors in this group were microsatellite unstable and showed loss of protein expression of one or two of the MMR proteins MLH1, PMS2, MSH2 or MSH6.…”