Comparative adherence to oral hormonal agents in older women with breast cancer

We aim to (1) compare compliance of anastrozole, letrozole, exemestane, and tamoxifen in women and (2) identify clinical factors associated with medication non-adherence and non-persistence. Female Medicare beneficiaries who were new users of anastrozole, letrozole, exemestane, or tamoxifen between 2007 and 2010 were analyzed. Multivariate-modified Poisson and Cox regression models were constructed to compare non-adherence and non-persistence, respectively, across the different oral agents. A total of 5,150 women were included: mean age was 76.4 years, 2352 initiated anastrozole, 1401 letrozole, 248 exemestane, and 1149 tamoxifen. Non-adherence and non-persistence were 41 and 49% respectively, with exemestane being associated with the worst non-adherence and non-persistence (RR 1.57, 95% CI 1.37-1.80, p < 0.001; HR 1.93, 95% CI 1.63-2.30, respectively, p < 0.001), followed by letrozole (RR 1.39, 95% CI 1.26-1.53, p < 0.001; HR 1.47, 95% CI 1.32-1.64, respectively, p < 0.001), and anastrozole (RR 1.16, 95% CI 1.05-1.27, p = 0.003; HR 1.14, 95%CI 1.03-1.27, respectively, p = 0.011), whereas tamoxifen was associated with the best compliance. Use of statins and osteoporosis medications was correlated with improved adherence (RR 0.89, 95 % CI 0.82-0.96, p = 0.002 and RR 0.84, 95 % CI 0.76-0.92, p < 0.001, respectively, for non-adherence) and persistence (HR 0.86, 95 % CI 0.79-0.94, p < 0.001 and HR 0.86, 95 % CI 0.78-0.96, p = 0.005, respectively, for non-persistence), but chronic kidney disease was correlated with worse non-persistence (HR 1.15, 95 % CI 1.04-1.33, p = 0.04). Age ≥ 70 years was also associated with worse compliance. Compliance to oral hormonal therapy varied depending on the type of agent, age, and concurrent medications, highlighting specific opportunities to improve adherence and persistence in older women with breast cancer.