Combined hormonal and progestogen-only pills increase the risk, but only slightly.
The combined oral contraceptive pill and the progesterone-only pill both increase the risk of breast cancer, but only marginally, new research suggests.
An analysis involving almost 30,000 women found that among those who used hormonal contraceptives for 15 years, an additional eight to 265 per 100,000 women developed breast cancer compared to those who did not use hormonal contraceptives.
The UK-based nested case-control study found an increase in the 15-year absolute excess incidence of breast cancer associated with five years of hormonal contraceptive use.
Researchers reported in PLOS Medicine that the incidence increased from 0.08% to 0.09% in women aged 16 to 20, corresponding to approximately eight additional breast cancer cases per 100,000 hormonal contraception users over that period.
A larger increase was observed in women aged 35 to 39, where the incidence increased from 2.0% to 2.2%, meaning 265 additional women in every 100,000 would receive a diagnosis.
“Similar levels of risk have been found with being overweight or drinking more than one standard drink of alcohol per day,” said Professor John Boyages, a radiation oncologist based at the Icon Cancer Centre in Sydney.
“The main finding in this study is that the risk was similar irrespective of contraceptive type and not to say that the pill was a major risk factor for breast cancer,” Professor Boyages told The Medical Republic.
Combined oral contraceptives have previously been linked to increases in breast cancer risk, but less is known about the effect of progestogen-only contraceptive approaches on breast cancer risk, despite their substantial increase in usage over the last decade. Almost half of breast cancer patients and 39% of cancer-free women received one or more prescriptions for a hormonal contraceptive prior to receiving their diagnosis. About half of the prescriptions were for progestogen-only contraceptives.
Women with at least one prescription for hormonal contraceptives had a 25% increase in the relative odds of developing breast cancer compared to women who did not use hormonal contraceptives.
Similar increases in the odds of developing breast cancer were reported when the type of hormonal contraceptive was considered: combined oral preparations by 23%, progestogen-only oral preparations by 26%, injectable progestogen by 25% and progestogen IUDs by 32%.
The meta-analysis of 12 studies from high-income countries explored the association between progestogen-only contraceptive use and breast cancer, and found an increase in similar magnitude with respect to relative breast cancer risk.
The inclusion of other high-income countries in the meta-analysis meant it was “reasonable” to say the findings were transferrable to an Australian population, said Professor Deborah Bateson, a clinical researcher from the University of Sydney.
Professor Bateson said the findings should not be a cause for concern and that the slight increase in breast cancer risk should be communicated to patients in an appropriate way.
“This is an important study, but there is no cause for alarm and no reason for people to stop using their preferred method of contraception – or for GPs to change their prescribing practices,” she told The Medical Republic.