Back to the nineties? Hormonal contraception and breast cancer

GPs of a ‘certain age’ remember well the panic after the Lancet paper in 1996 that showed a link between the combined pill and breast cancer. In combination with a health alert the year before linking ‘new generation’ COCP to VTE, it led to a ‘pill scare’ with worried patients, confused health professionals getting their heads around the difference between relative and absolute risks and it led to an increase in unintended pregnancies and terminations. So when I saw the media headlines last week following research PLOS, March 2023 linking hormonal contraception with breast cancer my initial reaction was ‘well, we know this already’. But closer reading reveals that this is important new evidence with significant new findings.

The 1996 data showed a small increase in breast cancer risk in women taking combined oral contraception. At the time, far fewer women compared to today took progestogen only pills or had LARCs and there was a lack of evidence (rather than evidence of lack) linking progestogen only methods to breast cancer. This new research  PLOS, March 2023 includes progestogen only methods of contraception. The research was an observational study based on a UK primary care database, a nested control study of 9,500 women aged under 50 diagnosed with breast cancer and 18,000 closely matched controls. They also did an associated meta-analysis looking at other studies of progestogen only contraception and breast cancer, studies which previously have shown inconsistent results.

Overall, the observational research showed that 44% of the women diagnosed with breast cancer compared to 39% of women in the control group had been prescribed hormonal contraceptives during an average of 3 years before a breast cancer diagnosis so the research relates to current or recent use. Crucially, about half the prescriptions were for progestogen only preparations. The headline finding therefore was that the risk of breast cancer was similarly and significantly raised irrespective of the type of hormonal contraception used, so it was the same for COCP, POP or LARCs including the IUS. This is a significant finding as it shows a link between progestogen containing contraception and breast cancer which is similar in magnitude to that with the combined pill.

But should we and our patients be worried? The paper quotes an increased relative risk of 20% to 30% in breast cancer risk associated with current or recent use of either combined or progestogen only contraceptives. That sounds a big number, as relative risks always do, but as in the pill scares of the 1990s it is the absolute risk that is crucial and this is much more reassuring. However, as breast cancer risk rises with age the absolute risks will also of course increase with age. Taking the data from the associated meta-analysis into account, they give some useful figures on absolute risk after 5 years of use of hormonal contraception:

• In women aged 16 to 20, the 15-year absolute increase in risk of breast cancer associated with oral combined or progestogen only contraceptives increases from 0.084% to 0.093%, or an extra 8 cases per 100,000 users -  so, a tiny increase of doubtful clinical significance
• In women aged 25 to 29, the 15-year absolute increase in risk of breast cancer associated with oral combined or progestogen only contraceptives increases from 0.5% to 0.57%, or an extra 61 cases per 100,000 users 
• In women aged 35 to 39, the 15-year absolute increase in risk of breast cancer associated with oral combined or progestogen only contraceptives increases from 2% to 2.2%, or an extra 265 cases per 100,000 users – so, still a small increase but starting to become more significant

In conclusion then, this new research is important in that it shows that the previously known link between breast cancer and combined oral contraception also applies to progestogen only contraceptives. There are many advantages to progestogen only methods of contraception for many women, but we can no longer include a lower breast cancer risk as one of them. If a woman is worried about increased breast cancer risk she may wish to avoid all hormonal methods of contraception.  The increase in absolute risk is very small, but it rises with age and this may be a factor for women to consider especially as they approach the perimenopause when progestogen only choices are increasingly used (and this data does not tell us what the risks may be in women aged over 50). This small increase in risk though needs to be balanced against the many other benefits of hormonal contraception, not just avoiding pregnancy (including ectopic) but also the known reduction in risk of ovarian and endometrial cancer. 

So, should we change practice? No, according to a useful summary of this evidence from the FSRH March 2023 who strongly reassure women that the increased risk is small and they should not stop using hormonal contraception because of this research. However, they do suggest that this information be included in individual discussions with women on the risks and benefits of all types of hormonal contraception.