Women with early-stage estrogen receptor (ER)-positive breast cancer show a third reduction in 15-year breast cancer mortality in correlation with receiving adjuvant tamoxifen. Although more effective than tamoxifen in postmenopausal women, aromatase inhibitors are ineffective in premenopausal women when used without ovarian suppression. Researchers herein investigated if aromatase inhibitors are beneficial for premenopausal women treated with ovarian suppression.

• Researchers retrieved individual patient data from randomized trials comparing aromatase inhibitors (anastrozole, exemestane, or letrozole) vs tamoxifen for 3 or 5 years in premenopausal women with ER-positive breast cancer receiving ovarian suppression (goserelin or triptorelin) or ablation, for inclusion in this meta-analysis.

• Four trials were identified (ABCSG XII, SOFT, TEXT, and HOBOE trials) including a total of 7,030 women with ER-positive tumors.

• Women allocated to an aromatase inhibitor had a lower rate of breast cancer recurrence than women assigned to tamoxifen.

• During years 0–4, the period when treatments differed, there was retrieval of the main benefit with a 3·2% (95% CI 1·8–4·5) absolute reduction in 5-year recurrence risk (6·9% vs 10·1%).

• Premenopausal women receiving ovarian suppression had reduced risk of breast cancer recurrence in correlation with receiving an aromatase inhibitor vs receiving tamoxifen.