Summary of findings 3. Aromatase inhibitors versus tamoxifen (indirect comparison)^a.

Aromatase inhibitors compared with tamoxifen for primary breast cancer prevention (based on network meta‐analysis findings)
Patient or population: women with above‐average risk of developing breast cancer Settings: prevention Intervention: aromatase inhibitors Comparison: tamoxifen
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Tamoxifen	Aromatase inhibitors
Overall breast cancer incidence Follow‐up: 3–16 years	49 per 1000	33 per 1000 ** (23 to 48)	RR 0.67 (0.46 to 0.98)	31,256 (5 RCTs)	⊕⊕⊝⊝ Lowb	—
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). ** Number needed to treat: 62 CI: confidence interval; RCTs: randomized controlled trial; RR: risk ratio.
GRADE Working Group grades of evidence High certainty: further research is very unlikely to change our confidence in the estimate of effect. Moderate certainty: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low certainty: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low certainty: we are very uncertain about the estimate.

^aThe findings are from indirect comparison (network meta‐analysis) of two RCTs comparing aromatase inhibitors with placebo and three RCTs comparing tamoxifen with placebo.
 ^bDowngraded two levels for partial lack of transitivity and inconsistency.