Combined oral contraceptives and cancer risk
- Women who are using combined oral contraceptives or have used them in the past 10 years are at a slightly increased risk of developing breast cancer. Cancer Council recommends that all women aged 50–74 years have a mammogram every two years through BreastScreen Australia.
- Women who have been using combined oral contraceptives for five or more years are at increased risk of developing cervical cancer. Cancer Council recommends that all women aged 25-74 years who have ever been sexually active have a Cervical Screening Test every five years.
- Combined oral contraceptives provide some protection against endometrial and ovarian cancer. The protective benefits of combined oral contraceptives extend to women at risk of hereditary ovarian cancer.
On balance, the strong evidence of reduced lifetime risk of endometrial and ovarian cancer outweighs the transient risks associated with breast and cervical cancer.
Hormonal contraceptives have been available in Australia since the 1960s. Oral contraceptives containing synthetic oestrogen and progestogen (combined oral contraceptives - COCs) remain the most popular reversible method of birth control in Australian women younger than 30 years. Modern oral contraceptives have smaller doses of hormones than the first formulations, which has greatly decreased the associated risks and side effects. Large population studies have shown that the use of COCs increases the risks of some cancers and lowers the risk of others.
Risks of combined oral contraceptives
Research indicates that women who are using COCs or have used them in the past 10 years are at a slightly increased risk of developing breast cancer. The risk begins to decline shortly after stopping use and returns to normal after 10 or more years of stopping use. Women who are currently using COCs have a 24% increased risk of breast cancer compared to women who have never used COCs. This is equal to an extra 1.5 cases of cancers per 10,000 women up to 10 years after stopping use for women who began using oral contraceptives from age 20-24 years. The risk begins to decline shortly after stopping use and returns to normal within 10 years of discontinuing use. A recent study found no evidence that current low-dose formulations added to the risk of early-onset breast cancer for women with BRCA1 and BRCA2 gene changes. (See Breast Cancer Screening chapter for more information on early detection.)
Long-term use of COCs (5 or more years) is associated with an increased risk of cervical cancer. An analysis of 24 epidemiologic studies found that the risk of cervical cancer increased with increasing duration of use. This is a transient increase in risk and starts to decline after stopping use. Ten years after stopping use, the risk is the same as that of women who have never taken COCs . Almost all cases of cervical cancer are caused by persistent infection with some high-risk types of the human papillomavirus (HPV) and the association of cervical cancer with COCs is as a co-factor in women who are already carrying HPV. (See Cervical Cancer Screening chapter for more information on early detection.)
Benefits of combined oral contraceptives
COCs provide long lasting protection against endometrial and ovarian cancer, which may persist for decades after stopping use. There is some suggestive evidence that oral contraceptives may also decrease the risk of bowel cancer. The protective benefits of COCs extend to women at risk of hereditary ovarian cancer.
New hormonal contraceptive options
The range of hormonal contraceptive options has increased significantly over the past 10 years. New options available in Australia include oral progestogens, progestogen implants and progestogen-bearing intrauterine devices. Hormonal contraceptive options, which may soon be introduced in Australia, include oestrogen/progestogen dermal patches and vaginal rings. Further research is required to assess the benefits and harms of long-term use (greater than five years) of these new hormonal contraception alternatives on cancer and other health risks.
- Cancer Council Australia – www.cancer.org.au
- Cancer Council Helpline – 13 11 20 (cost of a local call)
- World Health Organization- The Medical Eligibility Criteria for Contraceptive Use.
- Foran TM. New contraceptive choices across reproductive life. Med J Aust 2003 Jun 16;178(12):616-20 Available from: http://www.ncbi.nlm.nih.gov/pubmed/12797848.
- Yuzpe AA. Oral contraception: trends over time. J Reprod Med 2002 Nov;47(11 Suppl):967-73 Available from: http://www.ncbi.nlm.nih.gov/pubmed/12497670.
- 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 Jun 22;347(9017):1713-27 Available from: http://www.ncbi.nlm.nih.gov/pubmed/8656904.
- Milne RL, Knight JA, John EM, Dite GS, Balbuena R, Ziogas A, et al. Oral contraceptive use and risk of early-onset breast cancer in carriers and noncarriers of BRCA1 and BRCA2 mutations. Cancer Epidemiol Biomarkers Prev 2005 Feb;14(2):350-6 Available from: http://www.ncbi.nlm.nih.gov/pubmed/15734957.
- Franceschi S. The IARC commitment to cancer prevention: the example of papillomavirus and cervical cancer. Recent Results Cancer Res 2005;166:277-97 Available from: http://www.ncbi.nlm.nih.gov/pubmed/15648196.
- Iversen L, Sivasubramaniam S, Lee AJ, Fielding S, Hannaford PC. Lifetime cancer risk and combined oral contraceptives: the Royal College of General Practitioners' Oral Contraception Study. Am J Obstet Gynecol 2017 Jun;216(6):580.e1-580.e9 Available from: http://www.ncbi.nlm.nih.gov/pubmed/28188769.
- Fraser IS, Kovacs GT. The efficacy of non-contraceptive uses for hormonal contraceptives. Med J Aust 2003 Jun 16;178(12):621-3 Available from: http://www.ncbi.nlm.nih.gov/pubmed/12797849.
- 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 Oncol 2015 Sep;16(9):1061-1070 Available from: http://www.ncbi.nlm.nih.gov/pubmed/26254030.
- Bosetti C, Bravi F, Negri E, La Vecchia C. Oral contraceptives and colorectal cancer risk: a systematic review and meta-analysis. Hum Reprod Update 2009 Sep;15(5):489-98 Available from: http://www.ncbi.nlm.nih.gov/pubmed/19414526.
- Moorman PG, Havrilesky LJ, Gierisch JM, Coeytaux RR, Lowery WJ, Peragallo Urrutia R, et al. Oral contraceptives and risk of ovarian cancer and breast cancer among high-risk women: a systematic review and meta-analysis. J Clin Oncol 2013 Nov 20;31(33):4188-98 Available from: http://www.ncbi.nlm.nih.gov/pubmed/24145348.