Cohort Study: Levonorgestrel IUD Use Linked to Increased Breast Cancer Risk in Premenopausal Women
20 Oct, 2024 | 18:13h | UTCBackground: Levonorgestrel-releasing intrauterine systems (LNG-IUSs) are increasingly used, especially among Danish premenopausal women over 30 years old, as a preferred method of hormonal contraception. Previous studies have suggested an increased risk of breast cancer with LNG-IUS use but did not adequately address the duration of continuous use or account for other hormonal contraceptive exposures.
Objective: To assess the risk of breast cancer associated with continuous use of LNG-IUSs, accounting for other hormonal exposures.
Methods: In this nationwide Danish cohort study, 78,595 first-time LNG-IUS users aged 15–49 years from 2000 to 2019 were identified and matched 1:1 by birth year to nonusers of hormonal contraceptives. Exclusion criteria included prior hormonal contraceptive use within 5 years, previous cancer, postmenopausal hormone therapy, and pregnancy at baseline. Participants were followed from initiation until breast cancer diagnosis, other cancer, pregnancy, hormone therapy initiation, emigration, death, or December 31, 2022. Cox proportional hazards models adjusted for confounders estimated hazard ratios (HRs) for breast cancer associated with continuous LNG-IUS use.
Results: During a mean follow-up of 6.8 years, 1,617 breast cancer cases occurred: 720 among LNG-IUS users and 897 among nonusers. The mean age was 38 years. Continuous LNG-IUS use was associated with a higher breast cancer risk compared to nonuse (HR, 1.4; 95% CI, 1.2–1.5). HRs by duration were 1.3 (95% CI, 1.1–1.5) for 0–5 years, 1.4 (95% CI, 1.1–1.7) for >5–10 years, and 1.8 (95% CI, 1.2–2.6) for >10–15 years. Excess breast cancer cases per 10,000 users were 14 (95% CI, 6–23), 29 (95% CI, 9–50), and 71 (95% CI, 15–127), respectively. The trend test for duration was not statistically significant (P = .15).
Conclusions: Continuous use of LNG-IUSs was associated with an increased risk of breast cancer among women aged 15–49 years compared to nonuse of hormonal contraceptives. The absolute increase in risk was low.
Implications for Practice: Healthcare providers should inform women about the potential increased breast cancer risk associated with LNG-IUS use, especially considering its widespread and long-term use among premenopausal women. While the absolute risk increase is small, this information is essential for making informed contraceptive choices.
Study Strengths and Limitations: Strengths include the large, nationwide cohort and adjustment for multiple confounders. Limitations include potential underestimation of risk due to unrecorded LNG-IUS removals before the recommended duration, lack of a statistically significant trend with duration suggesting possible low statistical precision or non-causal association, and the possibility of unmeasured confounding.
Future Research: Further studies are needed to confirm these findings, clarify the causal relationship, and understand the mechanisms underlying the potential increased breast cancer risk with LNG-IUS use.