Oxford study: All forms of hormonal contraception raise breast cancer risk

A recently released study from the University of Oxford in the United Kingdom found that all forms of hormonal contraception raise breast cancer risk by 20-30%. This includes progestin-only contraceptives such as the mini-pill, levonorgestrel-IUD, implanted rod, and the Depo-provera arm injection.

While progestin-only (also known as progestogen-only) contraception has been touted as “safer” than the Pill due to its lack of synthetic estrogen — the culprit behind the increased risks of heart attack, blood clots, and stroke in Pill users — the results of this new study call into question rather than reinforce that label. This latest research is particularly timely given that progestin-only contraception is becoming increasingly popular worldwide as of late, as statistics from the United Kingdom show. 

What are the known risks of progestin-only contraception?

Live Action News has previously reported on the laundry list of side effects associated with progestin-only contraception, such as increased risk of cervical cancer, brain cancer, ectopic pregnancies in women who conceive while using the contraceptive, ovarian cysts, irregular bleeding, and depression. This latest study validates previous research finding an increased risk of breast cancer among users of progestin-only IUDs, and confirms that progestin-only pills are also associated with increased risk, just as the Pill is.

The new study further explores how much breast cancer risk may be increased, for how long, and the absolute excess risks, “meaning the additional number of women who would be expected to develop breast cancer in those who used oral contraceptives compared to those who did not.”

Who was studied and what did the researchers find? 

The Oxford researchers conducted a case-control study plus meta-analysis (reviewing previous research done on the topic) and conducted new research comparing 9,498 British women under age 50 who developed breast cancer between 1996 and 2017 with 18,171 peers (or “controls”) who did not (case-control study).

According to a press release, in the case-control study “there was a significant increase in risk of breast cancer associated with hormonal contraceptive use, regardless of whether the contraceptive last prescribed was a combined (oestrogen and progestogen) oral preparation (23%), a progestogen-only oral preparation (26%), an injected progestogen (25%), or a progestogen-releasing intra-uterine device (32%).”

Researchers found that when they added in data from the meta-analysis, every form of progestin-only contraception — the implant, the injection, the mini-pill, and the levonorgestrel-IUD — markedly increased breast cancer risk. 

Furthermore, in women who used oral hormonal contraceptives for five years, absolute excess risk of developing breast cancer during a 15-year timespan “ranged from eight in 100,000 women for use from age 16 to 20, to 265 in 100,000 for use from age 35 to 39.” 

Downplaying of breast cancer-hormonal contraception link

Given the widespread embrace of contraception, the study researchers, as well as experts commenting on their findings, downplayed the importance of the link.

Oxford Population Health’s statistical programmer Kirstin Pirie acknowledged:

The findings suggest that current or recent use of all types of progestogen-only contraceptives is associated with a slight increase in breast cancer risk, similar to that associated with use of combined oral contraceptives. Given that a person’s underlying risk of developing breast cancer increases with advancing age, the absolute excess risk of breast cancer associated with either type of oral contraceptive will be smaller in women who use it at younger ages.

She added, “These excess risks must, however, be viewed in the context of the well-established benefits of contraceptive use in women’s reproductive years.” 

Claire Knight, Senior Health Information Officer at Cancer Research UK, which funded the study, similarly stated, “Combined and progestogen-only hormonal contraception can increase the risk of breast cancer, but the risk is small” and encouraged hormonal contraception users to lower their breast cancer risk by “not smoking, eating a healthy balanced diet, drinking less alcohol, and keeping a healthy weight.”

Knight added, “There are lots of possible benefits to using contraception, as well as other risks not related to cancer,” but the truth is that hormonal contraception does not and cannot cure underlying health issues such as irregular or painful periods or fibroids, and there are other means of family planning and pregnancy prevention that don’t involve serious side effects and cancer risk.  

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