All types of hormonal contraceptives carry a small increased risk of breast cancer, according to research establishing a link with progestogen pills for the first time.
The use of progestogen is associated with a 20-30% higher risk of breast cancer, data analysis by University of Oxford researchers has established. This builds on previous work showing that use of the combined contraceptive pill, which contains oestrogen and progestogen, is associated with a small increase in the risk of developing breast cancer that declines after stopping taking it.
Claire Knight of Cancer Research UK, which funded the study, said the risk was small and should not discourage most people from taking the pill.
She said: “Women who are most likely to be using contraception are under the age of 50, where the risk of breast cancer is even lower. For anyone looking to lower their cancer risk, not smoking, eating a healthy balanced diet, drinking less alcohol, and keeping a healthy weight will have the most impact.
“There are lots of possible benefits to using contraception, as well as other risks not related to cancer. That’s why deciding to take them is a personal choice and should be done after speaking to your doctor so you can make a decision that is right for you.”
The research, which was published in PLOS Medicine, is based on data from 9,498 women who developed invasive breast cancer between ages 20 to 49, and 18,171 closely matched women without breast cancer.
The scientists found that 44% of women with breast cancer and 39% of women without breast cancer had a prescription for a hormonal contraceptive an average of three years before diagnosis, about half of whom were last prescribed a progestogen-only contraceptive.
The researchers estimated that the absolute excess risk of developing breast cancer over a 15-year period in women with five years’ use of oral contraceptives ranged from eight in 100,000 women for use from the age of 16 to 20, to 265 in 100,000 for use from the age of 35 to 39. They also found that the increased risk of breast cancer gradually declined in the years after stopping taking the pill.
Kirstin Pirie, a statistical programmer at Oxford Population Health and one of the lead authors, said that as breast cancer risk increased with age, younger women may consider the risk sufficiently small that it is outweighed by the benefits of contraceptive use during their reproductive years.
The findings are important as progestogen-only contraception is growing in popularity, with prescription levels matching those of combined oral contraceptives in 2020.
Dr Kotryna Temcinaite, the head of research communications at Breast Cancer Now, said there were some limitations to the study: “The study didn’t look at what hormonal contraceptives the women may have used in the past or consider how long they may have been on the progestogen-only contraception.
“It also didn’t factor in whether a family history of the disease contributed to their level of risk. So further work is needed to help us fully understand the impact of using this type of contraception.”
She added: “Breast cancer is rare in young women. A slight increase in risk during the time a woman uses hormonal contraceptive means only a small number of extra cases of the disease are diagnosed.”