Levonorgestrel-releasing intrauterine system use is associated with a decreased risk of ovarian and endometrial cancer, without increased risk of breast cancer. Results from the NOWAC Study

• Published in: Gynecologic oncology 2018-04, Vol.149 (1), p.127-132
• Main Authors: Jareid, Mie, Thalabard, Jean-Christophe, Aarflot, Morten, Bøvelstad, Hege M., Lund, Eiliv, Braaten, Tonje
• Format: Article
• Language: English
• Subjects: Adult; Aged; Breast neoplasms; Brystkreft / Breast Cancer; Carcinoma, Ovarian Epithelial; Cohort Studies; Contraceptive Agents, Female - administration & dosage; Contraceptives, Oral, Synthetic - administration & dosage; Eggstokkreft / Ovarian cancer; Endometrial Neoplasms - epidemiology; Epidemiologi medisinsk og odontologisk statistikk: 803; Epidemiology; Epidemiology, medical and dental statistics: 803; Female; Health sciences: 800; Helsefag: 800; Hormonal contraceptives; Humans; Intrauterine device; Intrauterine device, medicated; Levonorgestrel; Levonorgestrel - administration & dosage; Levonorgestrel / Levonorgestrel; Levonorgestrel-releasing intrauterine system; Life Sciences; Livmorkreft / Cervical cancer; Medisinske fag: 700; Middle Aged; Midical sciences: 700; Neoplasms, Glandular and Epithelial - epidemiology; Norway - epidemiology; Ovarian neoplasms; Ovarian Neoplasms - epidemiology; Prospective cohort study; Prospective Studies; Surveys and Questionnaires; Uterine neoplasms; VDP
• ISSN: 0090-8258; 1095-6859; 1095-6859
• DOI: 10.1016/j.ygyno.2018.02.006

•We present a population-based prospective cohort study of LNG-IUS users.•A mean of 4years use was associated with 47% reduced ovarian cancer risk.•Endometrial cancer risk was reduced by 78%.•We found no association between LNG-IUS use and breast cancer. Women with ovarian cancer have poor survival rates, which have proven difficult to improve; therefore primary prevention is important. The levonorgestrel-releasing intrauterine system (LNG-IUS) prevents endometrial cancer, and recent studies suggested that it may also prevent ovarian cancer, but with a concurrent increased risk of breast cancer. We compared adjusted risks of ovarian, endometrial, and breast cancer in ever users and never users of LNG-IUS. Our study cohort consisted of 104,318 women from the Norwegian Women and Cancer Study, 9144 of whom were ever users and 95,174 of whom were never users of LNG-IUS. Exposure information was taken from self-administered questionnaires, and cancer cases were identified through linkage to the Cancer Registry of Norway. Relative risks (RRs) with 95% confidence intervals (CIs) were estimated with Poisson regression using robust error estimates. Median age at inclusion was 52years and mean follow-up time was 12.5 (standard deviation 3.7) years, for a total of 1,305,435 person-years. Among ever users of LNG-IUS there were 18 cases of epithelial ovarian cancer, 15 cases of endometrial cancer, and 297 cases of breast cancer. When ever users were compared to never users of LNG-IUS, the multivariable RR of ovarian, endometrial, and breast cancer was 0.53 (95% CI: 0.32, 0.88), 0.22 (0.13, 0.40), and 1.03 (0.91, 1.17), respectively. In this population-based prospective cohort study, ever users of LNG-IUS had a strongly reduced risk of ovarian and endometrial cancer compared to never users, with no increased risk of breast cancer.