21 November 2024 –
Translation and summary, comments by Cancer Rose, 20 November 2024
The use of intrauterine contraceptive systems that release levonorgestrel (a synthetic progesterone-type hormone that blocks ovulation) continuously, such as the ‘Mirena’ IUD for example, is increasing.The use of these devices is the preferred hormonal contraception for premenopausal women over the age of 30 in Denmark.
An increased risk of breast cancer was found in women using hormonal contraception in a previous study, which concluded: ‘The risk of breast cancer was higher in women who were currently or recently using contemporary hormonal contraceptives than in women who had never used hormonal contraceptives, and this risk increased with duration of use; however, the absolute increases in risk were small’.
However, this study was not designed to examine the risk of breast cancer with continuous use.
A recent study carried out in Denmark and published in JAMA in October 2024 by Lina Steinrud Mørch, from the Danish Cancer Institute in Copenhagen, assessed the risk of breast cancer with continuous use of a levonorgestrel-releasing device, taking into account other hormonal exposures.
Method: Registry study
This is a registry study: based on the Danish national registries, all persons who started using a hormone-releasing intrauterine device for the first time and who were aged from 15 to 49, between 2000 and 2019, were selected and matched to the year of birth of non-users of hormonal contraceptives, from the start of the device insertion. Participants were followed from the date the intrauterine device was inserted until the diagnosis of breast cancer, or until the diagnosis of another cancer, pregnancy, initiation of post-menopausal hormone therapy, death or any other intercurrent event…
Exclusion criteria were the use of other hormonal contraceptives in the 5 years preceding the index date, previous use of post-menopausal hormone therapy, and previous cancer.
Results and discussion
This Danish national study demonstrated an association between the use of the hormonal continuous-release device and an increased risk of breast cancer in women aged between 15 and 49.
According to the authors, although the absolute risk of breast cancer is low in young women, this study showed an excess risk of 14 per 10,000 women. The risk did not increase with the duration of use.
The authors did not find a clear dose-response relationship between the increased risk of breast cancer and the increased duration of use; they believe this could be due to the lower number of women who used this type of IUD for more than 10 years, or to the fact that some women had their IUD removed and this was not taken into account in the registry data. This would underestimate the risk of breast cancer in the study.
Given the increase in the use of hormonal continuous-release devices in women of a certain age at risk of breast cancer, and its likely long-term use, information on the risk of breast cancer should accompany discussions on the benefits and risks of these contraceptives between healthcare professionals and users.
What we can conclude
The risk of breast cancer is slightly increased with hormone-releasing intrauterine devices, but is probably lower for younger women, as their baseline risk of breast cancer is statistically lower.
This risk is similar to that of other hormonal contraceptives[1] [2].
While the researchers ensured that the two populations of women were matched on criteria such as age, weight and education, other behaviours such as smoking or alcoholism (so-called ‘possible’ risk factors) were not assessed, which is a limitation of this study because it is possible that the habits of women not taking contraceptives (perhaps more concerned about their health and/or a ‘natural’ lifestyle) are different from those using hormonal contraception.
The increased risk of breast cancer among users of hormone-based intrauterine devices is admittedly low, but the authors themselves state that users should be informed. This risk must be weighed against the benefits of this type of contraceptive, which is used both as a contraceptive and as a treatment for women with heavy and prolonged periods.
Women should be aware that most types of hormonal contraceptives are associated with a slight increase in the risk of breast cancer, and this study adds another type of hormonal contraceptive to the list.
References
[1] Selon une expertise du Centre international de recherche sur le cancer (CIRC) menée en 2005 et actualisée en 2012, les pilules combinées entraîneraient une légère hausse du risque de cancers du sein, du col de l’utérus et du foie. https://www.e-cancer.fr/Comprendre-prevenir-depister/Reduire-les-risques-de-cancer/ Traitements-hormonaux/Pilules-contraceptives
- * S. Morch L., et al. Contemporary Hormonal Contraception and the Risk of Breast Cancer. N Engl J Med. 2017; 377: 2228-2239.
- * Jennie L Lovett, Margo A Chima, Juliana K Wexler, Kendall J Arslanian, Andrea B Friedman, Chantal B Yousif, Beverly I Strassmann, Oral contraceptives cause evolutionarily novel increases in hormone exposure: A risk factor for breast cancer, Evolution, Medicine, and Public Health, Volume 2017, Issue 1, January 2017, Pages 97–108, https://doi.org/10.1093/emph/eox009
- * Meta-analyse Hormonal Contraception and the Risk of Breast Cancer in Women of Reproductive Age: A Meta-Analysis
- * Meta-analyse au RU, publication de Danielle Fitzpatrick, Combined and progestagen-only hormonal contraceptives and breast cancer risk: A UK nested case–control study and meta-analysis
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