RELATION OF FAMILY HISTORY OF CANCER AND ENVIRONMENTAL-FACTORS TO THERISK OF COLORECTAL-CANCER - A CASE-CONTROL STUDY

The relation of a family history of cancer and environmental factors t o colorectal cancer was investigated in a case-control study conducted from 1992 to 1994 at 10 medical institutions in Japan using a self-ad ministered questionnaire, and 363 cases of colorectal cancer were comp ared with 363 controls matched for sex and age. A family history of co lorectal cancer was positively associated with colon cancer (odds rati o (OR)=2.0, 95% confidence interval (CI) 1.03-3.87) and rectal cancer (OR=2.1 CI 0.94-4.48), but a family history of other cancers did not i ncrease the risk. The proportion of patients with a family history of colorectal cancer within first-degree relatives was 12.4% - appreciabl y higher than figures previously reported in Japan. On the other hand, the incidence of hereditary non-polyposis colorectal cancer was 1.4%, and lower than previous estimates. Among dietary factors, a western-s tyle diet significantly increased the risk of both colon and rectal ca ncer (OR=2.3 CI 1.30-3.88 and OR=2.1 CI 1.26-3.63, respectively). Cons umption of rice was protective against both colon and rectal cancer (O R=0.5 CI 0.31-0.82 and OR=0.3 CI 0.18-0.65, respectively). Animal meat , oily food, fish, vegetables and fruit were shown to affect the risk, but no statistically significant correlation was found. Among other f actors, constipation increased the risk of colon cancer (OR=2.0 CI 1.0 2-3.76) and consumption of coffee raised the risk of rectal cancer (OR =1.7 CI 1.07-2.82). Our findings suggest that a family history of colo rectal cancer is an important risk factor for this disease, and does n ot contradict the hypothesis that the risk of colorectal cancer in Jap an may be influenced by westernization of lifestyle. However, we were unable to find conclusive evidence that familial clustering of this di sease is strongly affected by environmental factors or genetic disease s such as hereditary non-polyposis colorectal cancer.