Hormonal contraceptives increase cancer risk for some women

Taking hormonal contraceptives, such as the pill, adds to breast cancer risk for women with BRCA1 gene abnormalities who have a heightened lifetime risk for this cancer, according to a new study led by the Peter MacCallum Centre (Peter Mac) and Cancer Council Victoria.

BRCA1 and BRCA2 are genes which usually help protect against breast cancer; women who inherit an abnormal version of one of these genes have a very high risk of breast cancer. Abnormalities in BRCA1 or BRCA2 genes occur in just 1 in 400 (0.2%) of the Australian population; however, people with these inherited abnormalities account for about 5% of all cases of breast cancer.

The new research involved almost 5400 women who did not have cancer when they joined one of several long-term Australian, European, Canadian or US-based studies between 1991 and 2019. Participants used the mini and combined pills, hormonal implants and injections, and hormone-containing intrauterine devices.

Most of the women (3882) had BRCA1 abnormalities and, among these, 488 later developed breast cancer. A smaller group of 1509 women had BRCA2 abnormalities, and while 191 developed breast cancer this was deemed inconclusive.

“Women with BRCA1 abnormalities who used hormonal contraceptives, such as the pill, for at least a year had increased risk of subsequently developing breast cancer compared with women who did not use hormonal contraceptives,” said Peter Mac’s Professor Kelly-Anne Phillips.

“Also, breast cancer was more common in these women who used a hormonal contraceptive for longer.”

There was an overall 29% increase in relative risk on average, but this varied with how long hormonal contraceptives were used for. While shorter-term use results in only small increases in risk, use for longer durations can result in substantially larger increases in risk.

Phillips said more research is needed to properly understand if these contraceptives also affected breast cancer risk in women with BRCA2 abnormalities, as the results of this study for BRCA2 were inconclusive. She added that women with BRCA1 abnormalities should seek personalised advice, stating that “these medications provide excellent contraception and can have other health benefits, which must be weighed carefully against the possible increase in breast cancer risk”.

Co-lead author Professor Roger Milne, from Cancer Council Victoria, said the research “goes a long way to answering an important question about whether using hormonal contraceptives adds to cancer risk for an already vulnerable group”.

“Women with BRCA1 abnormalities may want to limit the time they use hormonal contraceptives, while the jury is still out for women with BRCA2 abnormalities,” Milne said.

Image credit: iStock.com/Rattankun Thongbun