Abstract

BACKGROUND: Prospective data from the Women's Health Initiative were analyzed to evaluate more than 800 possible risk factors for an association with colon cancer in postmenopausal women. METHODS: Data included 150,912 postmenopausal women between the ages of 50 and 79. The Cox proportional hazard regression analysis was used to identify risk factors independently associated with the development of colon cancer during a median follow-up time of 8 years. RESULTS: A total of 1,210 women developed colon cancer and 282 developed rectal cancer. Eleven risk factors were independently associated with an increased risk of colon cancer at the p < 0.001 level. In decreasing order of associated χ(2) values, they were age, waist girth (especially for subjects without diabetes), use of hormone therapy at baseline (protective), years smoked, arthritis (protective presumably because of medications used for treatment), relatives with colorectal cancer, lower hematocrit levels, fatigue, diabetes, less use of sleep medication, and cholecystectomy. Of the 11 factors, three were significantly associated with an increased risk of rectal cancer: age, waist, and not taking hormone therapy. CONCLUSIONS: The results provide additional support for the importance of waist girth, hormone therapy, smoking, NSAID use, diabetes, and cholecystectomy as risk factors for colon cancer. Some factors previously identified as influencing risk (exercise and black race) did not have a strong independent association with colon cancer in this analysis.