Incidence of hereditary non-polyposis colorectal cancer in a population-based study of 1137 consecutive cases of colorectal cancer

Background: Previous reports have indicated that 5-13 per cent of colorectal cancer is hereditary. However, the proportion of eases arising as a result of mutations in the hereditary non-polyposis colorectal cancer (HNPCC) genes remains to be determined. Methods This study is a part prospective, part retrospective review of all cases of colorectal cancer from a district hospital 'over 14 years. Some 1137 consecutive patients with colorectal cancer were questioned about their family history of cancer and details were logged on a database. For the past 4 years each case has been re-evaluated where possible. Results: Some 118 patients indicated initially that they had a first-degree relative with colorectal cancer, but on re- evaluation there were significant discrepancies. Only three cases (0·3 per cent) occurred in families which strictly fulfilled the criteria for HNPCC and there were no cases of familial adenomatous polyposis. A total of 16 patients (1·4 per cent) fulfilled looser criteria for HNPCC. Conclusion This population-based study has shown a lower frequency of familial bowel cancer than previous studies and may reflect a lower incidence of inherited mutations in the HNPCC DNA mismatch repair genes than is currently accepted.