The study, published in The New England Journal of Medicine and supported by the Novo Nordisk Foundation, adds to previous studies suggesting that modern combined pills may also be associated with a slight increased risk of breast cancer.
Presented at the 2017 San Antonio Breast Cancer Symposium, the study looked at 1.8 million women in Denmark, who were followed up for nearly 11 years on average. Led by the University of Copenhagen and the University of Aberdeen, researchers also showed that progesterone-only pills and the intra-uterine system seem to be associated with an increased risk of breast cancer, although further studies are needed to validate this finding.
Eluned Hughes, Head of Public Health and Information at Breast Cancer Now, said:
"That newer combined contraceptive pills may also carry a slight breast cancer risk is an important finding, and one that will help women make an even more informed decision when choosing to use the pill. As a safe and very effective method of preventing pregnancy, for many women the benefits will still outweigh the risks.
"The discovery surrounding progesterone-only pills and the intra-uterine system would suggest that all forms of hormonal contraception do slightly increase a woman’s risk of breast cancer, however further studies are needed to confirm this link.
"It’s important to keep in mind that breast cancer is rare in women before the menopause, with most women using the combined pill also being in their late teens, twenties and early thirties. We’d encourage all women to speak to their doctor or family planning clinic when starting or stopping the pill to ensure they fully understand the benefits and risks and are able to make an informed decision that’s right for them."