A Cochrane review included 4 studies with a total of 543 subjects. The levonorgestrel-releasing intrauterine device LNG-IUS in tamoxifen users led to a significant reduction in the incidence of endometrial polyps (follow-up 12 months, Peto OR 0.22, 95% CI 0.08 to 0.64, 2studies, n=212, I²=0%) and over a long-term follow-up period (24 to 60 months) (Peto OR 0.22, 95% CI 0.13 to 0.39, 4 studies, n = 417) and endometrial hyperplasia 8 follow-up 24 to 60 months, Peto OR 0.13, 95% CI 0.03 to 0.67, 4 studies, n=417, I²=0%). Also the LNG-IUS led to a reduction in the incidence of endometrial hyperplasia over a long-term follow-up period (24 to 60 months) (Peto OR 0.13, 95% CI 0.03 to 0.67, four studies, n = 417, I² = 0%, moderate quality evidence). By 24 months of follow-up, abnormal vaginal bleeding or spotting occurred less frequently compared to 12 months of follow-up in the LNG-IUS treatment group but was still more common than the control group (Peto OR 7.26, 95% CI 3.37 to 15.66, 3 studies, n = 376, I² = 0%, moderate quality evidence). By 24 months of follow-up, abnormal vaginal bleeding or spotting occurred less frequently compared to 12 months of follow-up in the LNG-IUS treatment group but was still more common than the control group (Peto OR 2.72, 95% CI 1.04 to 7.10, 2 studies, n = 233, I² = 0%, moderate quality evidence). By 60 months of follow-up, no cases of abnormal vaginal bleeding or spotting were reported in either group. The numbers of events for the following outcomes were low: fibroids (n = 13), breast cancer recurrence (n = 18), and breast cancer-related deaths (n = 16).
Comment: The quality of evidence is downgraded by indirectness (lack of data on clinically important outcomes) and by imprecise results (limited study size for each comparison). "?>