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A new study confirms that reproductive factors and oral contraceptive (OC) use are not important considerations in determining the risk of colorectal cancer in women.
Although colorectal cancer has not been a major concern for those who prescribe oral contraceptives for their patients, the study, published in Epidemiology, offers definitive information gathered from 57,529 women who participated in a nationwide breast cancer screening program.1
"Women do not need to factor in the long-term risk of colon cancer when they make their decision about taking oral contraceptives," says Rebecca Troisi, FCD, research fellow with the National Cancer Institute (NCI) in Bethesda, MD, and lead author for the study. "This is a nice study in the sense that it’s a large cohort study which enabled examination of a lot of overall factors, as well as subfactors," observes Michael Rosenberg, MD, MPH, president of Health Decisions, a Chapel Hill, NC-based private group involved in reproductive research. "In the absence of really any likely mechanisms, I found this study fairly reassuring and not at all surprising."
NCI researchers began a cohort study of a subset of women who participated in the massive Breast Cancer Demonstration Project, cosponsored by the NCI and the Atlanta- based American Cancer Society. A baseline interview, telephone follow-up calls, and a mailed questionnaire were used to track study participants.
Women were asked about reproductive factors, use of birth control pills, and female hormones other than pills (excluding creams.) Colorectal cancer cases were ascertained on the follow-up questionnaire and by death certificates. A total of 330 cases of colorectal cancer were reported.
Researchers looked at age at menarche, parity, age at first birth, type of menopause, age at menopause, OC use, and duration of OC use in performing their statistical analysis.
"In summary, our cohort study revealed no relation between a number of reproductive factors and the subsequent risk of colorectal cancer or its subsites," researchers concluded. "In addition, there was little evidence that the effects of parity and oral contraceptive use are stronger in older women or for the proximal colon, as indicated in some earlier studies."
Two upcoming studies dealing with post-menopausal hormones and colorectal cancer will offer more evidence of a decrease in risk of colorectal cancer with post-menopausal hormone use, says Troisi. These studies may be of use for the clinician, but may be of no influence on women choosing to use oral contraceptives or hormone replacement therapy.
"I think when women are making the decision to take OCs, it’s really more for an immediate need rather than for long-term risks," she otes. "This is true of post-menopausal hormones as well, [where] I think epidemiologists may think that women are taking them because they want to lower their risk of cancer. The truth is there are severe symptoms that can go along with menopause, and that’s the reason women are making the decision to take them or not."
1. Troisi R, Schairer C, Chow W-H, et al. Reproductive factors, oral contraceptive use, and the risk of colorectal cancer. Epidemiology 1997; 8:75-79.