Family history and environmental risk factors for colon cancer.

BACKGROUND We analyzed the joint effect of environmental risk factors and family history of colorectal cancer on colon cancer. METHODS We used data from a case-control study conducted in northern Italy between 1992 and 1996 including 1225 cases with colon cancer and 4154 controls. We created a weighed risk factor score for the main environmental risk factors in this population (positive family history, high education, low occupational physical activity, high daily meal frequency, low intake of fiber, low intake of calcium, and low intake of beta-carotene). RESULTS Compared with the reference category (subjects with no family history of colorectal cancer and in the lowest tertile of the risk factor score), the odds ratios of colon cancer were 2.27 [95% confidence interval (CI) = 1.89-2.73] for subjects without family history and in the highest environmental risk factor score, 3.20 (95% CI = 2.05-5.01) for those with family history and low risk factor score, and 7.08 (95% CI = 4.68-10.71) for those with family history and high risk factor score. The pattern of risk was similar for men and women and no meaningful differences emerged according to subsite within the colon. CONCLUSIONS Family history of colorectal cancer interacts with environmental risk factors of colon cancer.