The following summary of the relationship of the pill to cancers and cardiovascular diseases is based on findings from World Health Organization studies in 11 countries and other major studies.1
Ovarian and endometrial cancer -- Combined oral contraceptives (COCs) protect against ovarian cancer and endometrial cancer. The protective effect is related to the duration of use for both. For ovarian cancer, the protection after one or two years of COC use continues for at least 15 years after discontinuing COC use. For endometrial cancer, the evidence for duration of protection has not been established.
Breast cancer -- A recent analysis of 54 epidemiological studies found a small increased risk of breast cancer while women are taking OCs and in the 10 years after stopping. However, researchers said it was not possible to determine if the slight risk was due to an earlier diagnosis of cancer among pill users, or the effects of the pill, or a combination of reasons.2
There is no evidence of increased risk of breast cancer diagnosed after menopause, when breast cancer most commonly occurs. Some concern remains about the increased risk among women who begin using the pill before age 20. However, because the incidence of breast cancer is so low in this age group, the absolute number of cases that may occur would be quite small. It is also important to keep in mind that the incidence of breast cancer varies among countries. The incidence is much higher in western Europe and the United States than in Latin American or Asian countries, so the small increased risk has much less impact in those countries where the incidence is low.
Cervical cancer -- Data are not sufficient to provide conclusions about the relationship of cervical cancer to pill use. Recent studies have shown that genital human papillomavirus (HPV), a sexually transmitted disease, is responsible for most of the world's 500,000 new cervical cancers each year.
Using the pill for longer than five years may increase a woman's risk of cervical cancer, although the pill does not cause the cancer. Women who use the pill for a long period should have regular cytology screening (Pap smears).
Cardiovascular disease -- Initial concerns about the relationship between the pill and heart problems or stroke stemmed from early studies involving women who took the high-dose formulations. The higher doses had a greater impact on such factors as blood pressure, cholesterol levels and the coagulation system, compared to the lower doses now used in most pills. The risk of cardiovascular disease among pill users is largely limited to women over age 35 who smoke.3
In 1995, preliminary research was released from a WHO study and other research that indicated that venous thromboembolism might be slightly higher for women using pills with the new progestins. The studies involved the progestins desogestrel and gestodene. (The study did not examine norgestimate, another new progestin in use.) Fortunately, the additional risk of mortality from venous thromboembolism is very low, estimated to be no higher than two to three deaths per million users. This compares favorably with all causes of mortality in pregnancy and with the risks that many people accept in daily life.4
-- William R. Finger
Footnotes
- World Health Organization. Oral contraceptives and neoplasia: Report of a WHO Scientific Group. WHO Technical Report Series No. 817. Geneva: World Health Organization, 1992; Schlesselman JJ. Net effect of oral contraceptive use on the risk of cancer in women in the United States. Obstet Gynecol 1995;85:793-801.
- Breast cancer and hormonal contraceptives: Collaborative reanalysis of individual data on 53 297 women with breast cancer and 100 239 women without breast cancer from 54 epidemiological studies. Lancet 1996; 347(9017):1713-27.
- Grimes D. The safety of oral contraceptives: Epidemiologic insights from the first 30 years. Am J Obstet Gynecol 1992;166 (6, suppl.):1950-54.
- Guillebaud J. Advising women on which pill to take. Br Med J 1995;311:1111-12
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