Relation of family history of cancer and environmental factors to the risk of colorectal cancer: a case-control study.

The relation of a family history of cancer and environmental factors to colorectal cancer was investigated in a case-control study conducted from 1992 to 1994 at 10 medical institutions in Japan using a self-administered questionnaire, and 363 cases of colorectal cancer were compared with 363 controls matched for sex and age. A family history of colorectal cancer was positively associated with colon cancer (odds ratio (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 increase the risk. The proportion of patients with a family history of colorectal cancer within first-degree relatives was 12.4%--appreciably 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-style diet significantly increased the risk of both colon and and rectal cancer (OR = 2.3 CI 1.30-3.88 and OR = 2.1 CI 1.26-3.63, respectively). Consumption of rice was protective against both colon and rectal cancer (OR = 0.5 CI 0.31-0.82 and OR = 0.3 CI 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 factors, constipation increased the risk of colon cancer (OR = 2.0 CI 1.02-3.76) 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 colorectal cancer is an important risk factor for this disease, and does not contradict the hypothesis that the risk of colorectal cancer in Japan may be influenced by westernization of lifestyle. However, we were unable to find conclusive evidence that familial clustering of this disease is strongly affected by environmental factors or genetic diseases such as hereditary non-polyposis colorectal cancer.