Omar 2010.

Methods	Randomised controlled trial
Participants	Pre‐ and postmenopausal women with early stage breast cancer who required adjuvant tamoxifen after completion of postoperative radiation and chemotherapy. 150 women randomised; 18 were excluded after randomization (8 from the control and 10 from the treatment group declined participation). At baseline, 9 women (4 from control and 5 from treatment) were excluded due to an unsuccessful hysteroscopy. Exclusion criteria included age > 60 years, contraindications for intrauterine device (such as pelvic inflammatory disease, uterine cavity > 8 cm), active liver disease, history of progestogen treatment since diagnosis of breast cancer, history of malignant disease other than breast cancer, allergy to polyethylene, and refusal to receive the levonorgestrel intrauterine system.
Interventions	Two interventions compared: Endometrial surveillance alone (transvaginal ultrasound at base, 12 and 24 months; hysteroscopy and endometrial sampling at base and 24 months) Endometrial surveillance with insertion of the levonorgestrel intrauterine system
Outcomes	Development of endometrial polyps at 24 months Endometrial hyperplasia at 24 months Submucosal fibroids at 24 months Abnormal vaginal bleeding or spotting at 12 months and 24 months Breast cancer‐related death at 12 months
Notes	Study funding: not reported.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Allocation by computer‐generated random number series.
Allocation concealment (selection bias)	Low risk	Pre‐prepared serially‐numbered sealed envelopes.
Blinding (performance bias and detection bias) All outcomes	Low risk	The pathologist was blinded to the randomization. Even though the provider and participant were not blinded given the clinical intervention (insertion of the LNG‐IUS), the blinding of providers and participants is considered very unlikely to influence the outcomes.
Incomplete outcome data (attrition bias) All outcomes	Low risk	After randomization, 18/150 (12%) of women were excluded (8 from the control and 10 from the treatment group declined participation). At baseline, 9/150 (6%) of women (4 from control and 5 from treatment) were excluded due to an unsuccessful hysteroscopy. At 12 months of follow‐up, 2/123 (2%) of participants [1 in control group (breast cancer‐related death) and 1 in treatment group (hysterectomy)] were lost to follow up. At 24 months of follow‐up (62 in the control group and 59 in the treatment group), 0 participants were lost to follow up. At both follow‐up time points, 121 women were included in the analyses. There were no evidence of differences in baseline data between women who completed and did not complete the study. These data are at low risk of attrition bias.
Selective reporting (reporting bias)	Low risk	All outcomes were reported as planned.
Other bias	Low risk	No additional bias to report.