Oral Contraceptives and Cancer, Part 2

by National Cancer Institute

(Page 2 of 2)

In a National Cancer Institute (NCI)-sponsored study published in 2003, researchers examined risk factors for breast cancer among women ages 20 to 34 compared with women ages 35 to 54. Women diagnosed with breast cancer were asked whether they had used OCs for more than 6 months before diagnosis and, if so, whether the most recent use had been within 5 years, 5 to 10 years, or more than 10 years. The results indicated that the risk was highest for women who used OCs within 5 years prior to diagnosis, particularly in the younger group.

3. How do oral contraceptives affect ovarian and endometrial cancer risk?

Studies have consistently shown that using OCs reduces the risk of ovarian cancer. In a 1992 analysis of 20 studies of OC use and ovarian cancer, researchers from Harvard Medical School found that the risk of ovarian cancer decreased with increasing duration of OC use. Results showed a 10 to 12 percent decrease in risk after 1 year of use, and approximately a 50 percent decrease after 5 years of use.

Researchers have studied how the amount or type of hormones in OCs affects ovarian cancer risk reduction. One of the studies used in the Harvard analysis, the Cancer and Steroid Hormone Study (CASH), found that the reduction in ovarian cancer risk was the same regardless of the type or amount of estrogen or progestin in the pill. A more recent analysis of data from the CASH study, however, indicated that OC formulations with high levels of progestin reduced ovarian cancer risk more than preparations with low progestin levels. In another recent study, the Steroid Hormones and Reproductions (SHARE) study, researchers investigated new, lower-dose progestins that have varying androgenic properties (testosterone-like effects). They found no difference in ovarian cancer risk between androgenic and nonandrogenic pills.

OC use in women at increased risk of ovarian cancer due to BRCA1 and BRCA2 genetic mutations has been studied. One study showed a reduction in risk, but a more recent study showed no effect.

The use of OCs has been shown to significantly reduce the risk of endometrial cancer. This protective effect increases with the length of time OCs are used, and continues for many years after a woman stops using OCs.

4. How do oral contraceptives affect cervical cancer risk?

Evidence shows that long-term use of OCs (5 or more years) may be associated with an increased risk of cancer of the cervix (the narrow, lower portion of the uterus). Although OC use may increase the risk of cervical cancer, human papillomavirus (HPV) is recognized as the major cause of this disease. Approximately 14 types of HPV have been identified as having the potential to cause cancer, and HPVs have been found in 99 percent of cervical cancer biopsy specimens worldwide.

A 2003 analysis by the International Agency for Research on Cancer (IARC) found an increased risk of cervical cancer with longer use of OCs. Researchers analyzed data from 28 studies that included 12,531 women with cervical cancer. The data suggested that the risk of cervical cancer may decrease after OC use stops. In another IARC report, data from eight studies were combined to assess the effect of OC use on cervical cancer risk in HPV-positive women. Researchers found a fourfold increase in risk among women who had used OCs for longer than 5 years. Risk was also increased among women who began using OCs before age 20 and women who had used OCs within the past 5 years. The IARC is planning a study to reanalyze all data related to OC use and cervical cancer risk.

5. How do oral contraceptives affect liver cancer risk?

Several studies have found that OCs increase the risk of liver cancer in populations usually considered low risk, such as white women in the United States and Europe who do not have liver disease. In these studies, women who used OCs for longer periods of time were found to be at increased risk for liver cancer. However, OCs did not increase the risk of liver cancer in Asian and African women, who are considered high risk for this disease. Researchers believe this is because other risk factors, such as hepatitis infection, outweigh the effect of OCs.

6. What screening tests are available for the cancers described?

Studies have found that regular breast cancer screening with mammograms reduces the number of deaths from breast cancer for women ages 40 to 69. Women who are at increased risk for breast cancer should seek medical advice about when to begin having mammograms and how often to be screened. A high-quality mammogram, with a clinical breast exam (an exam done by a professional health care provider), is the most effective way to detect breast cancer early.

Abnormal changes in the cervix can often be detected by a Pap test and treated before cancer develops. Women who have begun to have sexual intercourse or are age 21 should check with their doctor about having a Pap test. Researchers are working on developing screening tests for ovarian and endometrial cancer.

Women who are concerned about their risk for cancer are encouraged to talk with their health care provider.

About the Author

www.nci.nih.gov
The National Cancer Institute's research programs are extensive and contain many innovative initiatives. I invite you to explore our Web site to find out more about the exciting work being conducted here at NCI and by NCI-supported scientists throughout the country.