(Washington) All forms of hormonal birth control carry a slightly increased risk of breast cancer in women, including increasingly used progestin-only methods, according to a new study released Tuesday.
This slight increase in the risk of breast cancer must however be put into perspective in the face of the benefits derived from contraception, including the protection provided against other types of cancer, the researchers point out.
The increased risk of breast cancer was already well known for contraceptive methods combining progestin and estrogen.
But while the use of methods containing only a progestogen has been on the rise for years, little work has so far focused on their specific effect on the risk of breast cancer.
This actually turns out to be similar to estrogen-progestogen methods, concludes this study published in the journal PLOS medicine.
According to this work, women using hormonal contraception have an increased risk of about 20% to 30% of developing breast cancer – regardless of the mode of delivery (pill, IUD, implant or injection), or the formula used (oestroprogestogen or progestogen only).
This rate is similar to what previous work had estimated, including a large study, as early as 1996.
To give a better idea of what this represents, the researchers calculated the number of additional cases of breast cancer involved, knowing that the risks of developing this disease increase with age.
In the case of hormonal contraception taken for five years between the ages of 16 and 20, the number of women developing breast cancer out of 100,000 will be eight. Taken between ages 35 and 39, this represents 265 additional cases of breast cancer per 100,000 women.
Transient risk
“No one wants to hear that something they’re taking is going to increase their risk of breast cancer,” said Gillian Reeves, a professor at Oxford University and co-author of the study. But this is a “very small risk in terms of absolute risk”, she stressed during a press conference.
This risk must also be considered in the light of the benefits provided by hormonal contraception, “not only in terms of controlling pregnancies, but also because oral contraceptives provide fairly significant and long-term protection against other cancers in women. woman, such as endometrial ovarian cancer,” said Gillian Reeves.
In addition, the study confirms, as others have done before it, that the increased risk of breast cancer linked to hormonal contraception is transient: it declines in the following years when contraception is stopped.
These results “are reassuring, because the effect is modest”, commented Stephen Duffy, professor at Queen Mary University of London, who was not involved in this work.
This study was carried out using data from just under 10,000 women under the age of 50 who developed breast cancer between 1996 and 2017 in the United Kingdom, where progestogen-only contraceptives are today. today as widespread as those combining progestin and estrogen.
Contraceptives with progestin alone are recommended for breastfeeding women, or for those with contraindications to estrogen-progestogen pills, such as risks of cardiovascular disease, or in case of smoking after 35 years.
Among the “multiple factors” explaining the increase in their use, it may be that “women now take contraceptives later” in their lives, and therefore they present more of these conditions naturally, argued Gillian Reeves.