Benefit/risk for adjuvant breast cancer therapy with tamoxifen or aromatase inhibitor use by age, and race/ethnicity

In early adjuvant breast cancer trial reports, aromatase inhibitors more effectively reduced breast recurrence with lower risk of thromboembolic events and endometrial cancer than tamoxifen, while aromatase inhibitors had higher fracture and cardiovascular disease risk. We used data from updated patient-level meta-analyses of adjuvant trials in analyses to summarize the benefits and risks of these agents in various clinical circumstances. Baseline incidence rates for health outcomes by age and race/ethnicity, absent aromatase inhibitor, or tamoxifen use were estimated from the Women’s Health Initiative. Aromatase inhibitor and tamoxifen effects on distant recurrence were obtained from a meta-analysis of the Arimidex, Tamoxifen, Alone or in Combination (ATAC) and Breast International Group (Big-1-98) clinical trials. Impact on other health outcomes were obtained from meta-analyses of randomized trials comparing aromatase inhibitor to tamoxifen use and from placebo-controlled chemoprevention trials. All health outcomes were given equal weight when modeling net benefit/risk for aromatase inhibitor compared to tamoxifen use by breast cancer recurrence risk, age (decade), race/ethnicity, hysterectomy (yes/no), and by prior myocardial infarction. Over a 10-year period, the benefit/risk index was more favorable for aromatase inhibitor than for tamoxifen as adjuvant breast cancer therapy in almost all circumstances regardless of patient age, race/ethnicity, breast cancer recurrence risk, or presence or absence of a uterus. Only in older women with prior myocardial infarction and low recurrence risk was an advantage for tamoxifen seen. Using a benefit/risk index for endocrine adjuvant breast cancer therapy in postmenopausal women, benefit was higher for aromatase inhibitor use in almost all circumstances.