I have never used Mirena but the following report may be of interest:
Recent studies, particularly from Denmark (2024), indicate a potential 30–40% relative increase in breast cancer risk for users of hormonal IUDs like Mirena compared to non-users. However, the absolute increase is very low, with studies suggesting roughly 14–29 additional cases per 10,000 women over 5-10 years, which is considered a minor increase overall.
Key Findings on Mirena and Breast Cancer
- Study Data: A large Danish study tracking ~80,000 users found a 30-80% relative increase in risk depending on duration, but in absolute terms, the risk remained under 1% of users.
- Absolute Risk: The actual risk is small. One study found only 14 extra cases per 10,000 women after 5 years. Another estimate suggested 1 additional case of breast cancer for every 7,690 users.
- Duration of Use: While some data suggest risk increases with duration, others found the risk does not significantly increase with longer use.
- Mechanism: The slight increase may be due to the progestogen (levonorgestrel) in the IUD affecting the growth of pre-existing, undetected cells.
- Other Factors: The studies often could not fully account for lifestyle factors like obesity, alcohol, or smoking, which are major, independent risk factors for breast cancer.
- Risk vs. Benefit: Medical experts largely agree that for most women, the benefits of Mirena (contraception, treatment of heavy bleeding) still outweigh the small increased risk of breast cancer.
