Background: The role of a family history of selected neoplasms in first-degree relatives in the risk of gastrointestinal cancers has been investigated, but requires further quantification.

Methods: A case-control study was conducted in northern Italy on 628 histologically confirmed incident cases of stomach cancer, 766 cases of colon cancer, 456 cases of rectal cancer, and 1766 controls admitted to hospital for acute, nonneoplastic, non-digestive tract disorders.

Results: Significant associations were observed between a family history of gastric cancer and stomach cancer risk (relative risk [RR], 2.6), and between a family history of intestinal cancer and colon (RR, 2.4) and rectal cancer (RR, 1.7). There was a tendency for the risks to be above unity for a family history of stomach cancer and for a number of other cancer sites (including esophagus, intestines, liver, pancreas, gallbladder, and lung), and the RR were of borderline statistical significance for cancer of the liver and intestines. The RR for a family history of lung cancer was 1.5 for stomach, 1.2 for colon, and 1.3 for rectal cancer, with none of the estimates being significant. There was no consistent pattern of risk with reference to the type of first-degree relationship; the RR was similar for stomach cancer with reference to parents and siblings, and for colon and rectal cancer, it was only moderately higher with reference to siblings. Significant trends in risk with the number of first-degree relatives were observed for all three cancer sites investigated.

Conclusions: In terms of population attributable risk, approximately 8% of stomach cancers and 3% of colorectal cancers would be related to this familial component.