Lynch syndrome (LS), the most frequent form of hereditary colorectal cancer syndrome, is caused by germ-line mutations in the mismatch repair system genes. Recently, a new mechanism involving the epithelial cell adhesion molecule (EPCAM)/TACSTD1 gene has been shown to be responsible in cases with abnormal MSH2 expression. Of interest, 3' exons deletions of the EPCAM gene, which is located upstream of MSH2 in chromosome 2, are associated with MSH2 promoter hypermethylation. EPCAM protein, expressed in epithelial tissues, is encoded by the EPCAM/TACSTD1 gene. Our study's aim was to explore EPCAM expression in colorectal carcinomas of MSH2-associated LS cases to evaluate the usefulness of EPCAM protein expression in the algorithm approach to LS population screening. We included a total of 19 MSH2-negative colorectal carcinomas from 14 different patients in whom we were able to perform a complete germ-line analysis. Nine patients showed a deleterious germ-line mutation that involved the MSH2 gene in 3 instances and the EPCAM gene exon 9 in 6 instances. All patients harboring the EPCAM mutation belonged to the same family. Of the 19 colorectal carcinomas, EPCAM expression loss was seen in only 5 tumors, all of them from patients showing a germ-line EPCAM deletion. Of interest, 6 tumors from 3 different patients carrying the same germ-line EPCAM deletion showed normal EPCAM expression. In conclusion, owing to the high specificity of EPCAM protein expression to identify LS patients carrying an EPCAM deletion, we recommend adding EPCAM immunohistochemistry to the LS diagnostic algorithm in MSH2-negative colorectal carcinoma.
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