Breast cancer risk similar in oral contraceptives: Study

Combined oral contraceptives (COCP) containing oestrogen and progestogen are known to be associated with a small and transient increase in breast cancer risk, but new research from Oxford University shows a similar association with progestogen-only contraceptives.
 
Published in PLOS Medicine, the study comprised almost 10,000 women with breast cancer under the age of 50 and found a relative risk increase between 20–30%, regardless of whether women used the COCP, progestogen-only pill (mini-pill), injected progestogen (depo), progestogen implant or progestogen-releasing intrauterine devices (IUDs).
 
Dr Suzanne Pearson, senior medical educator at Sexual Health Victoria, told newsGP it is not the first study to show this association.
 
‘This has been a difficult area to collect information on, so this study is welcomed,’ she said.
 
‘It is consistent with other smaller studies that have not had a level of evidence where a change in practice would be recommended.’
 
In the study, the average time between the last prescription and breast cancer diagnosis was about three years, so the authors report the breast cancer risk is related to ‘current’ or ‘recent’ hormonal contraceptive use.
 
Dr Pearson says this increased breast cancer risk needs to be taken in context.
 
‘While 20–30% sounds high, it depends on the background risk of breast cancer, which is extremely rare in younger people,’ Dr Pearson said.
 
‘For example, there would be an estimated increase from around 500 to 561 cases over the next 15 years for users of hormonal contraception aged 25–29 years.
 
‘Although the increase in risk is similar in those aged over 40 years, the background risk of breast cancer is higher and the absolute numbers of breast cancers attributable to hormonal contraception use would be higher.’
 
The study does not give estimates for this age group.
 
Dr Pearson says while the evidence about the slight increase in risk of breast cancer in users of the combined pill has been available for many years, there is no suggestion in increased breast cancer mortality.
 
‘The evidence for breast cancer mortality is not available for users of progestogen-only methods. It is hoped similarly, the risk will not be increased,’ she said.
 
She says breast cancer is a complex disease and there are several reversible factors that contribute to it, including alcohol intake and obesity.
 
‘Any discussion of risks associated with the use of hormonal methods of contraception must be balanced against their considerable benefits,’ she said.
 
‘Our current practice is to inform potential users of combined hormonal methods about the slight increase in breast cancer associated with use, that the absolute number is age dependent, and that there is no evidence of an increase in breast cancer mortality in hormonal contraception users.
 
‘We would now recommend providing the same information for users of progestogen-only methods.
 
Dr Pearson reiterates that while the identified increased risk ‘sounds like a lot’, for young people it is an extremely small increase in the number of cases because the background risk is so low.
 
‘Most people seem happy to accept this risk and a small number do not,’ she said.
 
The researchers also highlight that ‘these excess risks must be viewed in the context of well-established benefits of contraceptive use in women’s reproductive years’.
 
Progestogen-only methods are safe choices for those with risk factors or history of deep vein thrombosis, migraines with aura or cardiovascular disease.
 
The long-active reversible contraceptives (LARCs) such as Mirena, Kyleena and Implanon NXT are over 99% effective and do not involve a pill burden.
 
‘Mirena is very effective for heavy menstrual bleeding and the rate of hysterectomy for heavy bleeding has decreased dramatically since it became available in Australia,’ Dr Pearson said.
 
‘Combined hormonal contraception has a beneficial effect on acne and period pain, and allows a person to manipulate their cycles. Their use is associated with a decrease in the risk of ovarian and uterine cancer.’
 
Some people cannot tolerate any hormonal contraception or prefer non-hormonal options. These include condoms, the diaphragm or copper IUD.
 
‘We see a number of people using condoms only,’ Dr Pearson said.
 
‘While condoms are effective at STI protection, they have a high typical failure rate for contraception.
 
‘Over the last few years, we have seen a number of young people choosing copper IUDs over hormonal contraception options, although in our clinics we continue to have more people choosing hormonal IUDs than copper IUDs.
 
‘Copper IUDs are effective methods of contraception and generally quite well liked. There are less GPs … who have experience in inserting copper IUDs, and we would encourage them to consider including this option.’
 
Sexual Health Victoria offers in-person and online training for contraception, IUD insertion, sexual health and unplanned pregnancy. See details on the organisation’s website.
 
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