Combined oral contraceptives and cancer risk

Oral contraceptives containing oestrogen and progestogen (known as combined oral contraceptives) are the most popular reversible method of birth control in Australian women under the age of 30.

Apart from preventing pregnancy, oral contraceptives provide some level of protection against endometrial and ovarian cancer. They are also associated with a slightly increased risk of breast cancer and, in a certain group of women, an increased risk of cervical cancer.

Cancer Council Australia's Public Health Committee has developed a position statement which provides women with background information about the risks and benefits of combined oral contraceptives, particularly in relation to cancer. It reaffirms the importance of regular screening for breast and cervical cancer for women in the relevant age groups.

Key messages

• 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.

Background

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.^[1] Modern oral contraceptives have smaller doses of hormones than the first formulations, which has greatly decreased the associated risks and side effects^[2]. 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

Breast cancer

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^[3]. 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^[3]. The risk begins to decline shortly after stopping use and returns to normal within 10 years of discontinuing use^[3]. 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^[4]. (See Breast Cancer Screening chapter for more information on early detection.)

Cervical cancer

Long-term use of COCs (5 or more years) is associated with an increased risk of cervical cancer^[5]. An analysis of 24 epidemiologic studies found that the risk of cervical cancer increased with increasing duration of use^[5]. 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 ^[5][6]. 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^[6][7][8][9]. There is some suggestive evidence that oral contraceptives may also decrease the risk of bowel cancer^[6]. The protective benefits of COCs extend to women at risk of hereditary ovarian cancer^[10].

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^[1]. Hormonal contraceptive options, which may soon be introduced in Australia, include oestrogen/progestogen dermal patches and vaginal rings^[1]. 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.

Further information

• 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.