Is the Mirena (levonorgestrel) IUD safe for patients with hormone-dependent breast cancer?

Mirena IUD and Hormone-Dependent Breast Cancer

The Mirena (levonorgestrel-releasing) IUD is generally contraindicated in patients with current hormone-dependent breast cancer, though it may be considered for specific indications like endometrial protection in tamoxifen users after careful risk-benefit discussion. 1

Current Breast Cancer: Category 4 Contraindication

For women with active, current breast cancer, the levonorgestrel IUD represents an unacceptable health risk (US MEC Category 4). 1

• The Society for Maternal-Fetal Medicine explicitly lists current breast cancer as a Category 4 condition (unacceptable risk) for levonorgestrel IUD use. 1
• In this scenario, the copper (non-hormonal) IUD is Category 1 (no restriction) and should be used instead if long-acting reversible contraception is desired. 1
• Barrier methods (condoms, diaphragms) and copper IUDs are the recommended alternatives for contraception in breast cancer survivors. 1

Special Case: Tamoxifen Users for Breast Cancer Treatment

The evidence becomes more nuanced for women already diagnosed with hormone-dependent breast cancer who are taking tamoxifen:

Endometrial Protection Benefits

• The NCCN recommends the levonorgestrel IUD as first-line contraception for patients on tamoxifen for chemoprophylaxis, specifically because it protects against tamoxifen-induced endometrial changes. 2
• A Cochrane meta-analysis of three randomized trials (359 breast cancer patients) found the levonorgestrel IUD reduced endometrial polyps (OR 0.22,95% CI 0.13-0.39) and endometrial hyperplasia (OR 0.13,95% CI 0.03-0.67) without showing increased breast cancer recurrence or cancer-related deaths. 3
• Another meta-analysis reported no increased incidence of breast cancer recurrence (RR 0.12,95% CI 0.02-0.91) in tamoxifen patients using the levonorgestrel IUD. 2

Breast Cancer Risk Concerns

However, the safety regarding breast cancer recurrence remains controversial and not definitively established: 1, 2

• A 2024 Swedish national cohort study (514,719 LNG-IUD users) found a 13% increased risk of breast cancer development (adjusted HR 1.13,95% CI 1.10-1.17) in healthy women using the device. 4
• The risk was particularly elevated in women with a family history of breast cancer, showing 1.63 additional cases per 10,000 person-years. 4
• A 2020 meta-analysis showed increased breast cancer risk in LNG-IUS users overall (OR 1.16,95% CI 1.06-1.28), with higher risk in women ≥50 years (OR 1.52,95% CI 1.34-1.72). 5

Clinical Decision-Making Algorithm

For women with established hormone-dependent breast cancer on tamoxifen:

1. First-line recommendation: Non-hormonal copper IUD for contraception without endometrial concerns. 1, 2

2. Consider levonorgestrel IUD only if:

   • Patient has significant tamoxifen-induced endometrial pathology or high risk for it
   • Patient has been counseled about the controversial and insufficient evidence regarding breast cancer recurrence risk 1, 2
   • The endometrial protection benefit outweighs theoretical breast cancer concerns in the individual case

3. Avoid entirely if: Patient has active/current breast cancer not yet treated or in early treatment phase (first 6 months). 1, 2

Key Clinical Pitfalls

• Do not assume amenorrhea on tamoxifen means infertility - effective contraception is still required. 2
• Combined hormonal contraceptives (pills, patches, rings) are absolutely contraindicated due to VTE risk in cancer patients. 2
• The ESO-ESMO consensus panel recommends against levonorgestrel IUD in the absence of definitive safety data, favoring alternative non-hormonal contraception for breast cancer survivors. 1
• Patients must be informed that abnormal vaginal bleeding/spotting is significantly more common with levonorgestrel IUD at 12 months (OR 7.26,95% CI 3.37-15.66) and 24 months (OR 2.72,95% CI 1.04-7.10). 3

Bottom Line

For active hormone-dependent breast cancer: use copper IUD or barrier methods. For breast cancer survivors on tamoxifen with endometrial concerns, the levonorgestrel IUD may be considered after thorough counseling about uncertain breast cancer recurrence data, but non-hormonal options remain safer first-line choices. 1, 2