AIs versus tamoxifen for premenopausal ER-positive early-stage breast cancer in women receiving ovarian suppression

For women with early-stage ER-positive breast cancer, adjuvant tamoxifen reduces 15-year breast cancer mortality by a third. Aromatase inhibitors (AIs) are more effective than tamoxifen in postmenopausal women, but are ineffective in premenopausal women when used without ovarian suppression. Individual patient level meta-analysis of 7030 women from four randomized trials found that using an aromatase inhibitor rather than tamoxifen for 3 or 5 years for ER-positive early-stage breast cancer in premenopausal women receiving ovarian suppression reduces the risk of breast cancer recurrence. The main benefit was seen in years 0-4, the period when treatments differed, with a 3.2% absolute reduction in 5-year recurrence risk. There was no further benefit, or loss of benefit, in years 5-9 or beyond year 10.