Family history of colorectal adenomatous polyps as a risk factor for colorectal cancer.

The aim of this study was to evaluate the risk of common colorectal cancer among first-degree relatives of patients with colorectal adenomatous polyps. In a population screening programme, 59406 subjects underwent an immunochemical faecal occult blood test. In a medical check-up-based cross-sectional study, 6139 subjects had a colonoscopic examination. They were divided into two groups, according to the results of a questionnaire on family history of colorectal adenomatous polyps, and the detection rates for colorectal cancer were compared in the groups positive or negative for a family history of colorectal adenomatous polyps. In the screening programme-based cross-sectional study, the detection rate for colorectal cancer was 0.57% (95% confidence interval (CI): 0.38-0.76) and 0.15% (95% CI: 0.12-0.18) in subjects with and without a family history of colorectal adenomatous polyps, respectively, showing a significant difference in the detection rate for colorectal cancer between the two groups (P<0.05). In the medical check-up-based cross-sectional study, the detection rate for colorectal cancer was 2.31% (95% CI: 1.15-3.47) and 0.53% (95% CI: 0. 34-0.72) in subjects with and without a family history of colorectal adenomatous polyps, respectively, indicating a significant difference between the two groups (P<0.05). These findings indicate that first-degree relatives of patients with colorectal adenomatous polyps have an elevated risk for common colorectal cancer, and that people with a family history of colorectal adenomatous polyps should be considered as a priority group for colorectal cancer screening.