Does the Mirena (levonorgestrel) IUD increase the absolute risk of breast cancer?

Mirena IUD and Breast Cancer Risk

The Mirena (levonorgestrel-releasing) IUD is associated with a small but statistically significant increase in absolute breast cancer risk, with the most recent and highest quality evidence showing approximately 1.6 additional breast cancer cases per 10,000 person-years of use, particularly in women with a family history of breast cancer. 1

Absolute Risk Increase

The 2024 Swedish national cohort study—the largest and most recent investigation involving over 514,000 LNG-IUD users—demonstrated a 13% increased relative risk of breast cancer (adjusted HR 1.13,95% CI 1.10-1.17) compared to non-users. 1 More importantly for clinical decision-making:

• The absolute excess risk translates to 1.63 additional breast cancer cases per 10,000 person-years 1
• This risk is substantially amplified in women with a family history of breast cancer, showing a significant additive interaction (19% relative excess risk for interaction, p<0.002) 1

Context and Magnitude of Risk

To put this in clinical perspective:

• Baseline breast cancer incidence in reproductive-age women (20-49 years) is approximately 72 per 100,000 women annually 2
• The LNG-IUD increases this baseline risk modestly but measurably 1
• This increase is smaller than the breast cancer risk associated with combined oral contraceptives, where current users show a relative risk of 1.24 2

Conflicting Evidence Considerations

Earlier studies showed conflicting results:

• A 2011 Finnish-German case-control study found no increased risk (adjusted OR 0.99,95% CI 0.88-1.12) 3
• A 2020 meta-analysis showed increased risk across all age groups (OR 1.16,95% CI 1.06-1.28), with higher risk in women ≥50 years (OR 1.52) 4
• A 2025 umbrella review found no statistically significant association (OR 1.00,95% CI 0.70-1.41) 5

However, the 2024 Swedish study supersedes these findings due to its superior methodology: nationwide registry data, larger sample size, propensity score matching, and competing risk analysis. 1

Clinical Guideline Framework

The U.S. Medical Eligibility Criteria (2010) classifies breast cancer scenarios for LNG-IUD use: 2

• Current breast cancer: Category 4 (unacceptable health risk) - do not initiate 2
• Past breast cancer with no evidence of disease for 5 years: Category 3 - theoretical risks usually outweigh advantages 2
• Family history of breast cancer: Category 1 - no restriction, though this predates the 2024 interaction data 2

Risk-Benefit Algorithm

For women WITHOUT family history of breast cancer:

• The small absolute risk increase (1.6 cases per 10,000 person-years) is generally outweighed by contraceptive efficacy and non-contraceptive benefits (reduced endometrial cancer risk by 33%, ovarian cancer by 14%, cervical cancer by 9%) 1

For women WITH family history of breast cancer:

• Exercise heightened caution given the significant additive interaction 1
• Consider alternative contraception (copper IUD has no breast cancer association) 3
• If LNG-IUD is chosen, implement close breast surveillance 1, 4

For women with current or recent (<5 years) breast cancer:

• Absolutely contraindicated - remove promptly if already in place 2, 6

Critical Caveats

• The observed effect, while statistically significant, represents a small absolute risk increase that must be weighed against proven benefits 1
• The association does not prove causation due to observational study design limitations 1, 4
• Age appears to modify risk, with potentially greater effects in older users 4
• Duration of use may influence risk, though the 2024 study did not stratify by duration 1