Any type of hormonal contraceptive may increase the risk of breast cancer, research from the University of Oxford has suggested.
Although experts have stressed that this should not discourage people from taking the pill, the findings have prompted questions. How concerned should people be?
Why was this study done?
About 842 million women worldwide use modern methods of contraception, according to a UN study from 2019.
The prevalence of specific contraceptive methods varies widely globally. It has also shifted over time due to changes in policies, healthcare systems, and access to various methods, as well as the development of new technologies.
It has been known for decades that use of combined oral contraceptives is associated with a small increase in the risk of breast cancer. But until now, there has been limited data about the effect of progestogen-only contraceptives.
Use of these contraceptives has increased substantially in some countries over the last decade. In England, for example, there were almost as many prescriptions in 2020 for oral progestogen-only contraceptives, often known as the mini-pill, as for combined oral contraceptives.
Given the increasing use of progestogen-only contraceptives, it is important to understand how their use is associated with breast cancer risk.
What did the researchers find?
They studied 9,498 women aged under 50 diagnosed with breast cancer between 1996 and 2017, to assess the relationship between a woman’s recent use of hormonal contraceptives and their risk of breast cancer. They also looked at 18,171 women without breast cancer, who acted as study controls.
Current or recent use of hormonal contraceptives was associated with a similarly increased risk of breast cancer, regardless of whether the preparation last used was oral combined, oral progestogen-only, injectable progestogen, progestogen implant, or a progestogen intrauterine device.
The findings suggest that there is a relative increase of about 20% to 30% in breast cancer risk associated with current or recent use of either combined oral or progestogen-only contraceptives.
What does that mean in practical terms?
In numerical terms, for every 100,000 women aged 16 to 20 who use progestogen-only or oral combined contraception, there are an extra eight cases of breast cancer. For those aged 35 to 39, there will be about 265 extra cases in 100,000.
“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, who led the study.
Were there any limitations to the study?
Yes. The lack of complete information on a woman’s prescription history meant this study was unable to assess the long-term associations of contraceptive use on breast cancer risk, although this should not have unduly affected the findings.
“It also didn’t factor in whether a family history of the disease contributed to their level of risk,” says Dr Kotryna Temcinaite, head of research communications at Breast Cancer Now. “So further work is needed to help us fully understand the impact of using this type of contraception.”
How concerned should be people be?
“I don’t really see that there’s any indication here to say that women need to necessarily change what they’re doing,” said Gillian Reeves, a professor of statistical epidemiology and director of the cancer epidemiology unit at the University of Oxford.
“Yes, there is an increase here, and yes, nobody wants to hear that something that they’re taking is going to increase their risk for breast cancer by 25%.”
But she stressed that when women are normally taking hormonal contraceptives, in their 20s and 30s, the rates of breast cancer are very, very low.
So why is the study important?
“The main purpose of doing this research was really to fill a gap in our knowledge,” said Reeves. “We’ve known for many years that combined oral contraceptives, which women have been using for decades, also have an effect on breast cancer risk, a small increase in risk, which is transient.
“We weren’t absolutely sure what the corresponding effect of these progestogen-only contraceptives would be. What we’ve shown is that they’re just the same in terms of breast cancer risk. They seem to have a very similar effect to the other contraceptives … the effect that we’ve known about for many years.
“I suspect that if women were prepared to accept those risks in the past, in return for the many benefits of taking hormonal contraceptives, then they may well be prepared to carry on doing that.”
Anything else to bear in mind?
The excess risks found in the study should be viewed in the context of the well-established benefits of contraceptive use in women’s reproductive years, said Pirie.
“Breast cancer is rare in young women,” added Temcinaite. “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.”
And for both types of contraceptives, if you stop using them, the added risk of breast cancer reduces over time, Temcinaite said. “If you’re worried about breast cancer and contraception, or are unsure of what type you’re using, talk to your doctor or family planning clinic.”
