Is Mirena (levonorgestrel) associated with an increased risk of breast cancer?

Mirena and Breast Cancer Risk

The levonorgestrel-releasing intrauterine system (Mirena/LNG-IUS) is associated with a modest increased risk of breast cancer, with current evidence showing approximately 13-26% relative risk increase, though this translates to a small absolute risk increase. 1, 2

Evidence for Increased Breast Cancer Risk

The most recent and highest quality evidence comes from a 2024 Swedish national cohort study of over 500,000 women, which demonstrated:

• 13% increased risk of breast cancer in LNG-IUS users compared to non-users (adjusted HR 1.13,95% CI 1.10-1.17) 1
• Significantly higher risk in women with family history of breast cancer, showing a 19% relative excess risk for interaction and 1.63 additional cases per 10,000 person-years 1
• The effect appears larger in older users (≥50 years: OR 1.52,95% CI 1.34-1.72) compared to younger women (<50 years: OR 1.12,95% CI 1.02-1.22) 2

A 2025 Australian nested case-control study of 176,601 cancer cases confirmed these findings, showing a 26% increased breast cancer risk (OR 1.26,95% CI 1.21-1.31) with LNG-IUS use 3

Contraindications in Breast Cancer Patients

Women with current hormone-dependent breast cancer should NOT use Mirena - this is classified as a Category 4 condition (unacceptable health risk) by the American College of Obstetricians and Gynecologists 4

For breast cancer survivors or those on tamoxifen:

• First-line recommendation: copper IUD (non-hormonal, Category 1 - no restriction) 4, 5
• Hormonal contraception is generally contraindicated in breast cancer survivors per ESO-ESMO guidelines 5
• LNG-IUS may only be considered as a last resort after thorough risk discussion, primarily for women with significant tamoxifen-induced endometrial pathology 4

Balancing Risks and Benefits

The breast cancer risk must be weighed against proven benefits:

Protective effects demonstrated:

• 33% reduced risk of endometrial cancer (adjusted HR 0.67,95% CI 0.56-0.80) 1
• 14% reduced risk of ovarian cancer (adjusted HR 0.86,95% CI 0.75-0.99) 1
• 9% reduced risk of cervical cancer (adjusted HR 0.91,95% CI 0.84-0.99) 1
• One Norwegian study showed even stronger protective effects: 47% reduced ovarian cancer risk and 78% reduced endometrial cancer risk, with no increased breast cancer risk (RR 1.03,95% CI 0.91-1.17) 6

Clinical Recommendations

For women considering LNG-IUS:

• Screen for personal and family history of breast cancer before prescribing 1
• Exercise particular caution in women ≥50 years old and those with family history of breast cancer, as they face higher relative risks 1, 2
• Balance the small absolute breast cancer risk increase against substantial endometrial and ovarian cancer risk reductions 1
• Consider non-hormonal alternatives (copper IUD) for women with multiple breast cancer risk factors (age, obesity, familial predisposition) 2

For breast cancer patients:

• Use copper IUD as first-line contraception 4, 5
• Barrier methods (condoms, diaphragms) are acceptable hormone-free alternatives 4, 5
• Permanent sterilization for those with completed childbearing 4
• Avoid all combined hormonal contraceptives due to VTE risk 4

Important Caveats

The observed breast cancer risk increase is small in absolute terms - the baseline risk in non-users must be considered when counseling patients 1. The 2025 Australian study noted that for etonogestrel implants (similar progestin-only method), breast cancer risk returned to baseline after cessation, suggesting the effect may be reversible 3. However, methodological limitations exist across observational studies, and confounding factors may account for some of the observed associations 2.

Close monitoring for breast cancer development is advisable, particularly in women with family history who choose to use LNG-IUS 1