Frequency of Deletions of EPCAM (TACSTD1) in MSH2-Associated Lynch Syndrome Cases

Abstract

Lynch syndrome is an autosomal dominant cancer predisposition syndrome characterized by loss of function of DNA mismatch repair enzyme MLH1, MSH2, MSH6, or PMS2. Mutations in MLH1 and MSH2 account for ϳ80% of the inherited cases. However, in up to 20% of cases suspected of having a germline mutation in MSH2 due to loss of MSH2 expression, a germline mutation is not identified. Recent studies have shown that some Lynch syndrome cases are due to 3= EPCAM/TACSTD1 deletions that subsequently lead to MSH2 promoter hypermethylation. In this study, we examined the frequency of this novel mechanism for MSH2 inactivation in cases recruited through the Colon Cancer Family Registry and from the Mayo Clinic Molecular Diagnostics Laboratory. From the combined cohort, 58 cases were selected in which immunohistochemical staining suggested a mutation in MSH2 or MSH6, but no mutations were identified on follow-up testing. Of these 58 cases, 11 demonstrated a deletion of EPCAM/TACSTD1. Of cases with a deletion, the methylation status of the MSH2 promoter was confirmed in tumor tissue using methylation-sensitive PCR primers. One case showed MSH2 promoter hypermethylation in the absence of a detectable EPCAM/TACSTD1 deletion. These results indicate that approximately 20% to 25% of cases suspected of having a mutation in MSH2 but in which a germline mutation is not detected, can be accounted for by germline deletions in EPCAM/TACSTD1. These data also suggest the presence of other alterations leading to MSH2 promoter hypermethylation. Lynch syndrome is an autosomal dominant predisposition syndrome in which patients have a propensity to develop colorectal adenocarcinoma, endometrial carcinoma, sebaceous neoplasms, upper urinary tract urothelial carcinomas, central nervous system neoplasms, and ovarian and hepatobiliary neoplasms.1-4 The underlying genetic basis for this syndrome is the presence of a mutation in one of the DNA mismatch repair genes MLH1, MSH2, MSH6 or PMS2. [5][6][7][8][9][10] The defining phenotype of tumors from these patients is the presence of tumor microsatellite instability [11][12][13] and loss of protein expression of the affected enzyme in the tumor nuclei as detected by immunohistochemical staining.14 -16 The spectrum of mu-

ACMG technical standards and guidelines for genetic testing for inherited colorectal cancer (Lynch syndrome, familial adenomatous polyposis, and MYH-associated polyposis)

“…Tumors arising from EpCAM gene deletion demonstrate an MSI-high profile and loss of MSH2 and/or MSH6 by IHC. 76,77 Deletions in the 3′ region of the EpCAM gene can be detected using Southern blot, MLPA, or gene-targeted aCGH and should be analyzed in patients with IHC results showing loss of MSH2 and/or MSH6.…”

The molecular basis of EPCAM expression loss in Lynch syndrome-associated tumors

“…9 EPCAM deletions lead to a transcriptional read-through, silencing MSH2 9 and are estimated to cause Lynch syndrome in B20-25% of patients with MSH2-negative cancers, but no detectable MSH2 germline mutation. 10 This corresponds to B2-3% of Lynch syndrome patients. 10 A recent study demonstrated that concomitant lack of EPCAM and MSH2 protein expression is a feature highly specific for cancers from EPCAM deletion carriers, suggesting EPCAM immunohistochemistry as a potential tool for the identification of Lynch syndrome patients with EPCAM germline deletions.…”

“…10 This corresponds to B2-3% of Lynch syndrome patients. 10 A recent study demonstrated that concomitant lack of EPCAM and MSH2 protein expression is a feature highly specific for cancers from EPCAM deletion carriers, suggesting EPCAM immunohistochemistry as a potential tool for the identification of Lynch syndrome patients with EPCAM germline deletions. 11 However, EPCAM protein expression was retained in some cancers from EPCAM deletion carriers.…”

Gene discovery in familial cancer syndromes by exome sequencing: prospects for the elucidation of familial colorectal cancer type X

“…[70][71][72] EPCAM (also known as TACSTD1) deletion leading to MSH2 promoter methylation is another common genetic aberration causing Lynch syndrome. [73][74][75] Therefore, it is evident that only a proportion of hereditary non-polyposis colorectal cancer cases which fulfill the Amsterdam Criteria have germline mutations in mismatch-repair genes, which by 'definition' constitutes Lynch syndrome. As a result, families with a strong family history of colorectal cancer that do not have Lynch syndrome have been grouped as 'familial colorectal cancer-type X'; alternatively, some studies have referred to them as mismatch-repair gene mutation-positive and -negative families for Lynch syndrome and familial colorectal cancer type X, respectively.…”