Cervical cancer: Women who have used oral contraceptives for 5 or more years have a higher risk of cervical cancer than women who have never used oral contraceptives. The longer a woman uses oral contraceptives, the greater the increase in her risk of cervical cancer. One study found a 10% increased risk for less than 5 years of use, a 60% increased risk with 5–9 years of use, and a doubling of the risk with 10 or more years of use.9 However, the risk of cervical cancer has been found to decline over time after women stop using oral contraceptives.10–12
Endometrial cancer: Women who have ever used oral contraceptives have a lower risk of endometrial cancer than women who have never used oral contraceptives. Risk is reduced by at least 30%, with a greater risk reduction the longer oral contraceptives were used.13 The protective effect persists for many years after a woman stops using oral contraceptives.12,14,15 An analysis of women participating in the prospective NIH-AARP Diet and Health Study found that the risk reduction was especially pronounced in those long-time users of oral contraceptives who were smokers, obese, or exercised rarely.13
Ovarian cancer: Women who have ever used oral contraceptives have a 30% to 50% lower risk of ovarian cancer than women who have never used oral contraceptives.16–18 This protection has been found to increase with the length of time oral contraceptives are used13 and to continue for up to 30 years after a woman stops using oral contraceptives.17 A reduction in ovarian cancer risk with use of oral contraceptives is also seen among women who carry a harmful mutation in the BRCA1 or BRCA2 gene.19–21
Colorectal cancer: Oral contraceptive use is associated with 15% to 20% lower risks of colorectal cancer.12,14,22,23
How could oral contraceptives influence cancer risk?
Naturally occurring estrogen and progesterone stimulate the development and growth of some cancers (e.g., cancers that express receptors for these hormones, such as breast cancer). Because birth control pills contain synthetic versions of these female hormones, they could potentially also increase cancer risk.
In addition, oral contraceptives might increase the risk of cervical cancer by changing the susceptibility of cervical cells to persistent infection with high-risk HPV types (the cause of virtually all cervical cancers).
Researchers have proposed multiple ways that oral contraceptives may lower the risks of some cancers, including:
- suppressing endometrial cell proliferation (endometrial cancer)
- reducing the number of ovulations a woman experiences in her lifetime, thereby reducing exposure to naturally occurring female hormones (ovarian cancer)
- lowering the levels of bile acids in the blood for women taking oral conjugated estrogens (colorectal cancer)23
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2. Bassuk SS, Manson JE. Oral contraceptives and menopausal hormone therapy: relative and attributable risks of cardiovascular disease, cancer, and other health outcomes. Annals of Epidemiology 2015; 25(3):193-200 [PubMed Abstract]
4. Collaborative Group on Hormonal Factors in Breast Cancer. 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):1713–1727. [PubMed Abstract]
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10. International Collaboration of Epidemiological Studies of Cervical Cancer, Appleby P, Beral V, et al. Cervical cancer and hormonal contraceptives: collaborative reanalysis of individual data for 16,573 women with cervical cancer and 35,509 women without cervical cancer from 24 epidemiological studies. Lancet 2007; 370(9599):1609–1621. [PubMed Abstract]
11. Roura E, Travier N, Waterboer T, et al. The influence of hormonal factors on the risk of developing cervical cancer and pre-cancer: Results from the EPIC Cohort. PLoS One 2016; 11(1):e0147029. [PubMed Abstract]
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13. Michels KA, Pfeiffer RM, Brinton LA, Trabert B. Modification of the associations between duration of oral contraceptive use and ovarian, endometrial, breast, and colorectal cancers. JAMA Oncology 2018; doi:10.1001/jamaoncol.2017.4942Exit Disclaimer. [PubMed Abstract]
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15. Collaborative Group on Epidemiological Studies on Endometrial Cancer. Endometrial cancer and oral contraceptives: an individual participant meta-analysis of 27 276 women with endometrial cancer from 36 epidemiological studies. Lancet Oncology 2015; 16(9):1061-1070. [PubMed Abstract]
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18. Wentzensen N, Poole EM, Trabert B, et al. Ovarian cancer risk factors by histologic subtype: An analysis from the Ovarian Cancer Cohort Consortium. Journal of Clinical Oncology 2016; 34(24):2888-2898. [PubMed Abstract]
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