Adherence to Initial Adjuvant Anastrozole Therapy Among Women With Early-Stage Breast Cancer

Purpose Previous research evaluating adherence to tamoxifen therapy among women with early-stage breast cancer has revealed adherence estimates ranging from 25% to 96%. No previous studies have focused on adherence to adjuvant aromatase inhibitors. Methods We used longitudinal claims data from three large commercial health programs to estimate adherence with anastrozole therapy among women with early-stage breast cancer. Adherence was defined as the proportion of days that patients had medication available over the observation period (ie, days covered); women with fewer than 80% of days covered were defined as nonadherent. Results More than 12,000 women in the databases were found to have new anastrozole prescription claims during the period of study: 1,498 women were classified as having early-stage disease in one commercial health program (Plan A) data set, 1,899 women in another program (Plan B) data set, and 8,994 women in MarketScan, a commercial data set made up of several health programs. Mean adhe...