October 16, 2024

expert reaction to breast cancer in users of Levonorgestrel-Releasing Intrauterine Systems

A study published in JAMA looks at the use of Levonorgestrel-Releasing Intrauterine Systems and breast cancer risk. 

Dr Channa Jayasena, Reader in Reproductive Endocrinology, Imperial College London, said:

The Levonorgestrel-Releasing Intrauterine Systems (LNG-IUS) is a highly effective form of contraceptive for women. Unlike contraceptive pills, LNG-IUS releases a progesterone-like hormone directly into the womb.  This means that levels of the hormone are much lower than when you take it as a tablet. It is well known that prolonged use of the contraceptive pill slightly increases breast cancer risk. However, we have always assumed that the LNG-IUS would not increase breast cancer risk due to the much lower levels of hormone exposure to the whole body. The results of this study are therefore highly unexpected. A large population of women taking LNG-IUS was compared with a similar sized population of women not taking any contraceptive medication. While the researchers tried to make sure that the two populations of women were matched for things like age, weight and education, other behaviours like smoking have not been measured. So, women not taking contraceptive medication may have been healthier in other ways compared to the LNG-IUS group.

The study found that there were 14 extra cases of breast cancer per 10,000 women in the group using LNG-IUS compared to those not using contraceptive medication. It is difficult to tell how this compares with taking the contraceptive pill which has been studied in different populations. It is unfortunate that this study did not compare breast cancer risk between the LNG-IUS and oral contraceptive pill. But it is important that smoking, alcohol and obesity are much more important risk factors for breast cancer than contraceptive medications.

We always need to be vigilant to new health risks from medical treatments, and this is no exception. My advice for women is that breast cancer risk caused by LNG-IUS is not established but warrants a closer look.”

Dr Mangesh Thorat, Honorary Reader in Wolfson Institute of Population Health, Queen Mary University of London and Consultant Breast Surgeon, Homerton University Hospital, Queen Mary University of London (QMUL), said:

“This new large Danish study adds to the existing literature evaluating the risk of breast cancer in women using hormonal forms of contraception. The study specifically investigated the use of hormonal intrauterine devices, commonly known as hormonal coils, for example – Mirena coil. Similar to the British study (Fitzpatrick and colleagues) published last year, this study shows a small increase in the risk of breast cancer associated with the use of such coils. The existing evidence suggests that the increase in the risk is similar to that with oral contraceptive use. It is worth noting that this association has been known for at least a few years and a broad consensus exists among the medical fraternity that the overall benefits of hormonal contraception outweigh the harms like such small increase in the risk of developing breast cancer. Furthermore, as the baseline risk of breast cancer is lower in younger individuals, any increase in the risk associated with the use of hormonal coil is also smaller. The risk increases with increasing age and it is reasonable for women near 40 years of age to have a discussion with their healthcare practitioner regarding non-hormonal modes of contraception.”

‘Breast Cancer in Users of Levonorgestrel-Releasing Intrauterine Systems’ by Mørch et al. was published in JAMA at 16:00 UK time on Wednesday 16^th October 2024. 

DOI: 10.1001/jama.2024.18575

Declared interests

Dr Channa Jayasena: “No Conflicts to Declare”

Dr Mangesh Thorat: “No Conflicts to Declare”