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 poss ible markers for increased risk. Design: Case-control family study. Pa tients: Relatives of colorectal cancer patients and of matched control patients from a one-surgeon practice. Methods: Family medical histori es were obtained for 7493 first-degree relatives and 1015 spouses of 5 23 case-control pairs. Reported diagnoses of colorectal cancer in rela tives were verified in 79% of instances. Results: By case-control anal ysis, 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 befo re 45; and 1.8 times greater (CI, 1.2 to 2.9) with case patients diagn osed at 45 years or older; and was independent of gender, type of rela tive, site of cancer, and type of cancer (single or multiple). The cum ulative incidence, among first-degree relatives was greater for case p atients than for control patients (P < 0.001), and in case patients, g reater for those diagnosed before 55 years of age (P < 0.001). The cum ulative 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, resp ectively, and was 2.4% +/- 0.6% in relatives of control patients. Conc lusions: First-degree relatives of patients with common colorectal can cer have an increased risk for colorectal cancer. This risk is greater if diagnosis was at an early age and is greater when other first-degr ee relatives are affected. This increased risk should be considered wh en formulating screening strategies.