RISK OF COLORECTAL-CANCER IN THE FAMILIES OF PATIENTS WITH ADENOMATOUS POLYPS

Background. The adenoma-adenocarcinoma sequence in colorectal cancer s uggests an increased risk of colorectal cancer in the families of pati ents with adenomatous polyps. Methods. A random sample of participants in the National Polyp Study who had newly diagnosed adenomatous polyp s were interviewed for information on the history of colorectal cancer in their parents and siblings, The risk of colorectal cancer in famil y members was analyzed according to the characteristics of the patient s with adenomas and in comparison with a sample of patients' spouses, who served as controls. Results. Among the patients with adenomas, 119 9 provided information on whether they had a family history of colorec tal cancer. After the exclusion of families for which information was incomplete and of 48 patients who had been referred for colonoscopy so lely because they had a family history of colorectal cancer, there wer e 1031 patients with adenomas, 1865 parents, 2381 siblings, and 1411 s pouse controls. The relative risk of colorectal cancer, adjusted for t he year of birth and sex, was 1.78 for the parents and siblings of the patients with adenomas as compared with the spouse controls (95 perce nt confidence interval, 1.18 to 2.67). The relative risk for siblings of patients in whom adenomas were diagnosed before 60 years of age was 2.59 (95 percent confidence interval, 1.46 to 4.58), as compared with the siblings of patients who were 60 or older at the time of diagnosi s and after adjustment for the sibling's year of birth and sex and a p arental history of colorectal cancer. The risk increased with decreasi ng age at the time of the diagnosis of adenoma (P for trend <0.001). T he relative risk for the siblings of patients who had a parent with co lorectal cancer, as compared with those who had no parent with cancer, was 3.25 (95 percent confidence interval, 1.92 to 5.52), after adjust ment for the sibling's year of birth and sex and the patient's age at diagnosis. Conclusions. Siblings and parents of patients with adenomat ous polyps are at increased risk for colorectal cancer, particularly w hen the adenoma is diagnosed before the age of 60 or - in the case of siblings - when a parent has had colorectal cancer.