December 2024 | George M. Pikler, M.D., Ph.D., FACP, Lead Oncology Advocate N1X10
Intrauterine devices (IUDs) are commonly used contraceptive devices. Older versions contain copper as their active ingredient. Newer “hormonal” IUDs slowly release a synthetic hormone -progesterone- called levonorgestrel and are known as LNG-IUDs. The device mimics the body’s natural progesterone hormone. Their use has been rising in popularity in recent years. With an average efficacy rate of over 99 per cent, they are considered one of the most effective methods of contraception that does not require further interventions such as taking a daily dose or monthly administration. Fertility is readily restored when they’re removed.
The LNG-IUD is widely used for the treatment of menorrhagia, dysmenorrhea, and for contraception. Some women have one inserted for these reasons, even if they don’t need contraception. Many women experience pain on insertion or spotting in the first few months of use. But compared to other contraceptives, they generally find IUDs very acceptable and continue to use them.
The link between the use of LNG-IUDs and breast cancer the risk of remains unclear. Two recent studies assessed the breast cancer risk with continuous use of an LNG-IUD.
The first, a Danish nationwide study (1), tracked nearly 80,000 women who started hormonal IUDs across two decades. The study compared these people to an equal number who did not use hormonal IUDs. There were 720 cases of breast cancer in the hormonal IUD group, and nearly 900 in the other group. Unfortunately, this was not a randomized controlled trial. The researchers “adjusted” their results to account for some differences between the two groups (including education, age, number of children, and some other medicines and medical conditions). After this “adjustment”, the numbers pointed in a different direction: towards a higher risk of breast cancer among people who used a hormonal IUD. However, the authors seem not to have adjusted for other important risk factors for breast cancer, such as body weight, alcohol use, smoking and physical activity. Therefore, this study can not conclusively say the LNG-IUD caused the breast cancer -just that there is an “association” or “link.”
The second, a much larger recent study from Sweden (2) based on data from more than half a million users of hormonal IUDs. This suggested only a 13% relative risk increase in breast cancer – much smaller than the risk increases in the Danish study. This would mean an additional 1.46 cases of breast cancer for every 10,000 women per year. The Swedish study also looked at other cancers. The results suggested a decreased risk of cancers of the cervix, ovaries and endometrium. The authors concluded that the observed effect is small for breast cancer and the results are limited by the observational study design. Clinical recommendations regarding the use of LNG-IUDs should carefully weigh its potential benefits and risks. Close monitoring is advisable for the potential development of breast cancer, particularly among women with a family history of breast cancer.
