A recent study has sparked significant discussion in the medical community, revealing that women using hormonal intrauterine devices (IUDs)—specifically those releasing levonorgestrel—may face a higher risk of breast cancer than those who do not use these contraceptives.
The findings contribute to a growing body of research indicating potential health risks associated with levonorgestrel-releasing IUDs, marketed in the U.S. as Mirena, Liletta, Kyleena, and Skyla.
Key Findings from the Study
Published on October 16 in JAMA, the study led by Dr. Mørch analyzed data from 157,190 women in Denmark, spanning from 2000 to 2019. Participants ranged in age from 15 to 49, with an average age of about 38. Notably, all participants had not used hormonal contraception for at least five years prior to the study, a critical factor in controlling for other hormonal exposures.
The research compared two groups: 78,595 women using levonorgestrel-releasing IUDs and 78,595 women with similar characteristics who did not use these devices. Participants were monitored until 2022 or until they were diagnosed with breast cancer, became pregnant, initiated postmenopausal hormone therapy, relocated, or passed away. The follow-up period extended up to 15 years.
The results indicated a 40% increased risk of developing breast cancer among women using LNG-IUDs, equating to approximately 14 additional cases per 10,000 women.
Dr. Mørch noted that “hormones like estrogen and progestin may stimulate the growth of hormone-sensitive tissues, including breast tissue,” which could account for the observed increased risk.
Contextualizing the Findings
While Dr. Mørch emphasized that there have been few studies specifically examining breast cancer risk linked to hormonal IUDs, existing research has echoed similar concerns. A 2020 study from England suggested a 20% to 30% relative risk for women using LNG-IUDs. Another investigation from 2017, which Dr. Mørch co-authored, also found a 20% increase in breast cancer odds associated with progestin-containing contraceptives, including birth control pills and injections.
The long-established connection between hormonal birth control and elevated breast cancer risk has drawn attention. However, some studies also suggest that oral contraceptives may reduce the risk of other cancers, such as ovarian and endometrial cancers.
Dr. Georgia Spear, a breast imaging expert at Endeavor Health, highlighted the importance of studies like this in understanding breast cancer risk but reassured that the overall likelihood of developing breast cancer while using levonorgestrel-releasing IUDs remains low.
Should You Be Concerned?
Experts urge caution but not alarm for those using or considering LNG-IUDs. Dr. Jillian LoPiano, an OB-GYN and chief health officer at Wisp, emphasizes the need for further research to apply these findings to U.S. demographics. “Breast cancer risk is multifaceted, influenced by genetics, lifestyle, and other factors,” she noted, adding that these findings should inform, not overwhelm, discussions between patients and healthcare providers.
Dr. Mørch acknowledged the study’s limitations, including its observational nature and the exclusion of low-dose hormonal IUDs.
Despite these caveats, Dr. Spear reiterated that for many, the benefits of contraception often outweigh the associated risks. “This study should not incite fear regarding contraceptive methods,” she said. Instead, it should prompt open discussions with healthcare providers, especially for individuals with a family history of breast cancer or other risk factors.
For those particularly concerned about hormone-related cancer risks, Dr. Mørch suggested considering non-hormonal IUDs, such as the copper IUD, or barrier methods like condoms as potentially safer alternatives. Low-dose hormonal IUDs may also present a viable option due to their reduced hormone levels compared to high-dose versions.