Differential Effectiveness of Aromatase Inhibitors in Hormone Receptor–Positive Breast Cancer

Adjuvant endocrine therapy (ET) for individuals with hormone receptor-positive (HR + ) breast cancer is recommended for at least 5 and up to 10 years after primary breast cancer treatments end. 1 Suboptimal ET adherence and early ET discontinuation are well-documented challenges that contribute to poorer HR + breast cancer outcomes.ET adherence and early discontinuation rates vary across studies, with estimates reported in 1 systematic review to range from 41% to 72% and 31% to of newer targeted therapies (ie, cyclin-dependent kinase [CDK]4 inhibitors such as ribociclib) that may be prescribed in the setting of high-risk, early-stage HR + breast cancer in combination with an AI such as letrozole or anastrozole. 7Future analyses using population-based data inclusive of these +