Women who currently use hormonal contraceptives (such as the combined pill, the progestogen-only pill and non-oral products such as the hormone-intrauterine system (IUS)) are at 20% increased risk of breast cancer than those who do not use them.
The new research from Rigshospitalet, University of Copenhagen in collaboration with the University of Aberdeen is published in New Engl. J. Medicine, today December 7, and is the largest prospective cohort study ever conducted on hormonal contraception and breast cancer.
The study followed 1.8 million Danish women below 50 years of age from 1995 to 2012 to assess breast cancer risk in users of different types of hormonal contraception as compared to women who had never used hormonal contraception.
During the study period 11,517 new breast cancers were detected. In current and recent users of any type of hormonal contraception, the risk of breast cancer was 20% increased.
There was little evidence of consistent differences in risk between users of combined oral contraceptives with different progestogens. Researchers did not detect an increased risk in former users who had used hormonal contraception for less than five years, while the increased risk in long-term users gradually decreased by time and disappeared five to ten years after stopping.
Users of progestogen only contraceptives (mainly pills and the hormone-intrauterine system (IUS)) also experienced an increased relative risk of breast cancer.
Professor Phil Hannaford who led the research team based in Aberdeen said: “Breast cancer is rare in young women. In this study, the absolute extra risk of breast cancer associated with use of hormonal contraception among all women age 15-49 years was 1.3 per 10,000 person-years, or one extra breast cancer for every 7,690 women using hormonal contraception for one year.
”Earlier this year, the world’s longest-running study of the effects of taking the contraceptive pill published its latest findings. The Royal College of General Practitioners’ (RCGP) Oral Contraception Study, also run from the Institute of Applied Health Sciences, University of Aberdeen, examined the very long term cancer effects associated with the pill- by following an original cohort of 46,000 women for up to 44 years. The study found an increased risk of breast and cervical cancer in current and recent pill users, risks which disappeared within approximately 5 years of stopping oral contraception. Importantly, the study also found that women who had ever used the pill were less likely to have colorectal, endometrial or ovarian cancer than women who had never used the pill- benefits that persisted for many years after stopping the pill, perhaps 30 or more years. And new cancer risks did not appear as the women got to the age when cancer becomes common.
”The similar breast cancer results in both cohort studies suggest that today’s pills have similar cancer risks and benefits as older preparations. If this suggestion is confirmed, then evidence from the Royal College of General Practitoners’ Study indicates that, like previous generations of users, today’s pill users do not increase their overall lifetime risk of cancer by choosing hormonal contraception. “