Cancer risk in relatives of patients with common colorectal cancer.

OBJECTIVE: To quantify any risk for colorectal cancer in first-degree relatives of patients with common colorectal cancer and to define possible markers for increased risk.
DESIGN: Case-control family study. PATIENTS: Relatives of colorectal cancer patients and of matched control patients from a one-surgeon practice.
METHODS: Family medical histories were obtained for 7493 first-degree relatives and 1015 spouses of 523 case-control pairs. Reported diagnoses of colorectal cancer in relatives were verified in 79% of instances.
RESULTS: By case-control analysis, the odds ratio was 1.8 (95% CI, 1.2 to 2.7) for one and 5.7 (CI, 1.7 to 19.3) for two affected relatives. By matched analysis of risk in relatives, the increased risk to parents and siblings was 2.1 times greater for case patients than for control patients (CI, 1.4 to 3.1); 3.7 times greater (CI, 1.5 to 9.1) with case patients diagnosed before 45; and 1.8 times greater (CI, 1.2 to 2.9) with case patients diagnosed at 45 years or older; and was independent of gender, type of relative, site of cancer, and type of cancer (single or multiple). The cumulative incidence among first-degree relatives was greater for case patients than for control patients (P < 0.001), and in case patients, greater for those diagnosed before 55 years of age (P < 0.001). The cumulative incidence (+/- S.E.) to age 80 was 11.1% +/- 1.3%, 7.3% +/- 0.8%, and 4.4% +/- 1.0% among relatives of case patients diagnosed before age 45 years, between 45 and 54 years, and at 55 years or older, respectively, and was 2.4% +/- 0.6% in relatives of control patients.
CONCLUSIONS: First-degree relatives of patients with common colorectal cancer have an increased risk for colorectal cancer. This risk is greater if diagnosis was at an early and is greater when other first-degree relatives are affected. This increased risk should be considered when formulating screening strategies.