BACKGROUND AND AIMS: Germline mutations in mismatch repair (MMR) genes cause a greatly increased\ud risk of cancer of the gastrointestinal and female reproductive tracts (hereditary non-polyposis colorectal\ud cancer (HNPCC)). Loss of MMR expression is common in colorectal cancer (CRC) overall. Such loss is\ud assumed to be acquired predominantly, although a population of CRC cases will include individuals with\ud unrecognised MMR mutations. This study examines the association between MMR gene expression and\ud family history of cancer among the CRC population.\ud \ud \ud METHODS: Individuals with CRC were identified from two well characterised populations: (1) consecutive\ud hospital patients (n = 644) and (2) a population based cases series (n = 249). CRC was examined for\ud expression of hMLH1 and hMSH2 using immunohistochemistry, and expression was related to family history using logistic regression.\ud \ud \ud RESULTS: hMLH1 and hMSH2 expression was assessed in 732 CRCs with 8% showing loss of expression.\ud No association was seen overall for hMLH1 or hMSH2 expression and family history of CRC. Loss of\ud hMSH2 was predicted by family history of extracolonic cancer (odds ratio (OR) 5.78 (95% confidence\ud interval (CI) 0.95–35.18)) and family history suggestive of HNPCC (OR 27.84 (95% CI 4.37–177.56)).\ud Loss of hMLH1 was not predicted by family history of extracolonic cancer or a family history suggestive of\ud HNPCC but was for a family history of at least two affected relatives (OR 4.88 (95% CI 1.25–19.03)).\ud \ud \ud CONCLUSIONS: Individuals with hMSH2 deficient CRC in the general population exhibit a family history and\ud other characteristics suggestive of HNPCC, and may carry germline MMR mutations. Loss of hMLH1 is only\ud associated with a strong family history of extracolonic cancer at older ages, suggesting a novel mechanism\ud of susceptibility
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