Tuuli Soini1, Ritva Hurskainen2, Seija Grénman3,4, Johanna Mäenpää5,6, Jorma Paavonen7,8, Heikki Joensuu9,10, Eero Pukkala11,12. 1. a Department of Obstetrics and Gynecology , Hyvinkää Hospital , Hyvinkää , Finland. 2. b Department of Obstetrics and Gynecology , Hyvinkää Hospital , Hyvinkää , Finland. 3. c Department of Obstetrics and Gynecology , Turku University Hospital , Turku , Finland. 4. d University of Turku , Turku , Finland. 5. e School of Medicine, University of Tampere, University of Tampere , Finland. 6. f Department of Obstetrics and Gynecology , Tampere University Hospital , Tampere , Finland. 7. g Department of Obstetrics and Gynecology , Helsinki University Hospital , Helsinki , Finland. 8. h University of Helsinki , Helsinki , Finland. 9. i Department of Oncology , Comprehensive Cancer Center, Helsinki University Hospital , Helsinki , Finland. 10. j Department of Oncology , University of Helsinki , Helsinki , Finland. 11. k School of Health Sciences, University of Tampere, University of Tampere , Finland. 12. l Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research , Helsinki , Finland.
Abstract
BACKGROUND: Prolonged steroid hormone therapy increases the risk of breast cancer, especially the risk of lobular cancer, but the effect of the levonorgestrel-releasing intrauterine system (LNG-IUS) use is controversial. In this study we aimed to test the hypothesis that risk for lobular breast cancer is elevated among LNG-IUS users. MATERIAL AND METHODS: We identified from the national Medical Reimbursement Registry of Finland the women aged 30-49 who had used LNG-IUS for the treatment or prevention of menorrhagia in 1994-2007, and from the Finnish Cancer Registry breast cancers diagnosed before the age of 55 and by the end of 2012. RESULTS: A total of 2015 women had breast cancer diagnosed in a cohort of 93 843 LNG-IUS users during follow-up consisting of 1 032 767 women-years. The LNG-IUS users had an increased risk for both ductal breast cancer [standardized incidence ratio (SIR) 1.20, 95% confidence interval (CI) 1.14-1.25] and for lobular breast cancer (SIR 1.33, 95% CI 1.20-1.46), as compared with the general female population. The highest risk was found in LNG-IUS users who purchased the device at least twice, whose SIR for lobular cancer was 1.73 (95% CI 1.37-2.15). CONCLUSIONS: The results imply that intrauterine administration of levonorgestrel is not only related to an excess risk of lobular breast cancer but also, in contrary to previous assumptions, to an excess risk of ductal breast cancer.
BACKGROUND: Prolonged steroid hormone therapy increases the risk of breast cancer, especially the risk of lobular cancer, but the effect of the levonorgestrel-releasing intrauterine system (LNG-IUS) use is controversial. In this study we aimed to test the hypothesis that risk for lobular breast cancer is elevated among LNG-IUS users. MATERIAL AND METHODS: We identified from the national Medical Reimbursement Registry of Finland the women aged 30-49 who had used LNG-IUS for the treatment or prevention of menorrhagia in 1994-2007, and from the Finnish Cancer Registry breast cancers diagnosed before the age of 55 and by the end of 2012. RESULTS: A total of 2015 women had breast cancer diagnosed in a cohort of 93 843 LNG-IUS users during follow-up consisting of 1 032 767 women-years. The LNG-IUS users had an increased risk for both ductal breast cancer [standardized incidence ratio (SIR) 1.20, 95% confidence interval (CI) 1.14-1.25] and for lobular breast cancer (SIR 1.33, 95% CI 1.20-1.46), as compared with the general female population. The highest risk was found in LNG-IUS users who purchased the device at least twice, whose SIR for lobular cancer was 1.73 (95% CI 1.37-2.15). CONCLUSIONS: The results imply that intrauterine administration of levonorgestrel is not only related to an excess risk of lobular breast cancer but also, in contrary to previous assumptions, to an excess risk of ductal breast cancer.