Hormonal contraceptives linked to higher breast cancer risk, new Australian study reveals

Pharma News: A new Australian study has shed light on whether hormonal contraceptives increase breast cancer risk for women with an already elevated lifetime risk.

Breast cancer remains the most common cancer among Australian women, with 20,973 women and 221 men expected to be diagnosed this year.

In the general population, current use of hormonal contraceptives is associated with a 20%-30% relative increase in the risk of breast cancer compared with never having used “the pill”. Longer duration of use is associated with higher risk and, although the relative risk reduces after cessation, it remains elevated for 5-10 years after cessation.

The research, led by Professor Kelly-Anne Phillips from Peter MacCallum Cancer Centre, examined data from nearly 5,400 women who carry the BRCA1 or BRCA2 gene mutations. These women were enrolled in various major longitudinal studies that monitored their health over time.

None of the participants had developed cancer at the time they joined the studies. The data revealed that the use of hormonal contraceptives, such as the mini-pill, combined pill, implants, injections, and intrauterine devices (IUDs), was common among this group.

For women with a BRCA1 mutation, the findings were significant. Use of hormonal contraceptives for at least one continuous episode of 12 months was associated with an average 29% increased relative risk of breast cancer compared with never use, but this varied with cumulative duration of use, with a proportional increase of 3% per year for each year of use. Risk was not associated with earlier age at first use or use before first birth.

Professor Phillips highlighted the study’s key outcome, saying “Hormonal contraceptives were associated with increased breast cancer risk for BRCA1 mutation carriers, especially if used for longer durations,” she explained. “Decisions about their use in women with BRCA1 mutations should carefully weigh the risks and benefits for each individual.”

By contrast, the authors found no evidence of an increased risk for breast cancer associated with use of hormonal contraceptives by BRCA2 mutation carriers. However, the analysis for BRCA2 was based on only 191 BC cases and the confidence intervals were wide. Despite this, Professor Phillips emphasised the need for further research to draw definitive conclusions.

While hormonal contraceptives remain among the most widely prescribed medicines globally, they offer effective contraception and additional health benefits in the treatment of polycystic ovarian syndrome, premenstrual dysphoric disorder, endometriosis, and reduce risks of ovarian and endometrial cancers, Professor Phillips noted.

The BRCA1 and BRCA2 genes play a crucial role in protecting against breast cancer. However, individuals who inherit abnormal versions of these genes face an elevated lifetime risk. While these mutations are rare, affecting just 0.2% of the Australian population, they are responsible for about 5% of all breast cancer cases.

Encouragingly, breast cancer survival rates have significantly improved. Between 1989 – 1993 and 2014 – 2018, five-year relative survival rates increased from 77% to 92%.

For those wanting to better understand their personal risk of breast cancer, Peter Mac offers an online tool called “iPrevent,” available here.

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