Levonorgestrel-releasing and copper intrauterine devices and the risk of breast cancer.

Background: This study compares the risk of breast cancer for levonorgestrel-releasing intrauterine devices (LNG(IUD)) versus copper IUDs (CU(IUD)) in women younger than 50 years of age.

Study Design: Retrospective, population-based, case-control study using cancer registers in Finland and Germany, powered to exclude a 1.5-fold risk of breast cancer.

Results: Analysis of 5113 breast cancer cases diagnosed 2000-2007 and 20,452 controls - matched by year of birth and area of residence - yielded relative risk estimates approaching unity with 95% CI crossing 1.0 for all comparisons, including ever-use of LNG(IUD) versus CU(IUD) (adjusted OR, 0.99; 95% CI, 0.88-1.12) and current use at time of diagnosis (adjusted OR, 0.85; 95% CI, 0.52-1.39), as well as for sub-analyses by country, age, tumor characteristics and period, recency and duration of use prior to diagnosis.

Conclusion: This study does not indicate an increased risk of breast cancer for users of LNG(IUD). No indications for tumor promotion or tumor induction were found.