Treatment adoption and relative effectiveness of aromatase inhibitors compared to tamoxifen in early breast cancer: A multi-institutional observational study

Since 2005, aromatase inhibitors (AIs) have been the adjuvant treatment of choice for postmenopausal women with early breast cancer (BC). In this study we characterize the adoption of AIs in Portugal, variables associated with treatment administration, and compare its effectiveness (either in monotherapy or sequential therapy) to tamoxifen monotherapy (TAM). This was a retrospective cohort study that included postmenopausal women with stage I-III hormone receptor (HR) positive BC diagnosed from 2006 to 2008 and treated with adjuvant endocrine therapy in four participating institutions. Of the 1283 eligible patients, 527 (41%) received an AI (16% as monotherapy, 25% as sequential therapy) and 756 (59%) TAM. Patients treated with AI had less differentiated tumors, with higher TNM stage, and were more frequently HER2-positive. Use of AI also differed by center (use range from 33% to 75%, p