Use of all hormonal contraceptives is associated with a small increase in the risk of breast cancer, according to a new study.
The research, published in the journal PLOS Medicine, found a relative increase of 20 to 30 per cent in breast cancer risk associated with both combined and progestogen-only contraceptives, whatever the mode of delivery.
The resaerchers at the University of Oxford, UK, and colleagues found that a 15-year absolute excess incidence is at most 265 cases per 100,000 users.
Use of combined oral contraceptives, containing both estrogen and progestogen hormones, has previously been associated with a small increase in breast cancer risk but there is limited data about the effect of progestogen-only contraceptives, the resaerchers said.
However, the use of progestogen-only contraceptives has increased substantially in recent years, with almost as many prescriptions in England for oral progestogen-only contraceptives as for combined oral contraceptives in 2020, they said.
The researchers analysed data from a UK primary care database, the Clinical Practice Research Datalink (CPRD), on 9,498 women under the age of 50 with invasive breast cancer diagnosed in 19962017, as well as data on 18,171 closely matched controls.
On average, 44 per cent of women with breast cancer and 39 per cent of matched controls had a hormonal contraceptive prescription, with about half the prescriptions being for progestogen-only preparations.
With five years use of either oral combined or progestogen-only contraceptives, the associated 15-year absolute excess incidence of breast cancer was estimated at 8 cases per 100,000 hormonal contraceptive users at age 1620 years and 265 cases per 100,000 users at age 3539 years.
The odds of breast cancer were similarly and significantly raised, regardless of whether the contraceptive used was a combined (estrogen and progestogen) oral preparation, a progestogen-only oral preparation, an injected progestogen, or a progestogen releasing intra-uterine device.
These results were combined with those from previous studies from high income countries, which included women from a wider age range.
"These 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," said Kirstin Pirie of University of Oxford.
"Given that the underlying risk of breast cancer increases with advancing age, the absolute excess risk associated with use of either type of oral contraceptive will be smaller in women who use it at younger rather than at older ages," Pirie said.
However, the resaerchers said these excess risks must be viewed in the context of the well-established benefits of contraceptive use in women's reproductive years.
