A PROSPECTIVE-STUDY OF FAMILY HISTORY AND THE RISK OF COLORECTAL-CANCER

Background. A family history of colorectal cancer is recognized as a r isk factor for the disease. However, as a result of the retrospective design of prior studies, the strength of this association is uncertain , particularly as it is influenced by characteristics of the person at risk and the affected family members. Methods. We conducted a prospec tive study of 32,085 men and 87,031 women who had not previously been examined by colonoscopy or sigmoidoscopy and who provided data on firs t-degree relatives with colorectal cancer, diet, and other risk factor s for the disease. During the follow-up period, colorectal cancer was diagnosed in 148 men and 315 women. Results. The age-adjusted relative risk of colorectal cancer for men and women with affected first-degre e relatives, as compared with those without a family history of the di sease, was 1.72 (95 percent confidence interval, 1.34 to 2.19). The re lative risk among study participants with two or more affected first-d egree relatives was 2.75 (95 percent confidence interval, 1.34 to 5.63 ). For participants under the age of 45 years who had one or more affe cted first-degree relatives, the relative risk was 5.37 (95 percent co nfidence interval, 1.98 to 14.6), and the risk decreased with increasi ng age (P for trend, <0.001). Conclusions. A family history of colorec tal cancer is associated with an increased risk of the disease, especi ally among younger people.