Use of the levonorgestrel-releasing intrauterine system and breast cancer.

OBJECTIVE The effect of exogenous hormones on the incidence of breast cancer has been extensively studied. Most studies regarding hormonal contraception have focused on combined oral contraceptives, and there is paucity of literature regarding nonoral and progestin-only contraceptives. The present study analyzed the relationship between breast cancer and use of the levonorgestrel-releasing intrauterine system. METHODS This study was based on data gathered from a large postmarketing study on levonorgestrel-releasing intrauterine system users (n = 17,360) carried out in Finland. The results present an incidence comparison between levonorgestrel system user data and the data on average Finnish female population (derived from the Finnish Cancer Registry), between 30 and 54 years of age. RESULTS Based on the 95% confidence intervals for the incidences of breast cancer, and the Fisher exact test, there is no indication of a difference between the levonorgestrel system users and average Finnish female population in any of the 5-year age groups. The incidence rate per 100,000 woman-years was for the age groups 30-34 years 27.2 and 25.5, for 35-39 years 74.0 and 49.2, for 40-44 years 120.3 and 122.4, for 45-49 years 203.6 and 232.5, and for 50-54 years 258.5 and 272.6, in the levonorgestrel system group and in Finnish female population, respectively. CONCLUSION The results suggest that the use of the levonorgestrel-releasing intrauterine system is not associated with an increased risk of breast cancer.