MEDICATION USE IN PATIENTS WITH HORMONE RECEPTOR POSITIVE BREAST CANCER

Although guideline-recommended long-term use of adjuvant hormone therapy (HT) is highly effective in improving breast cancer outcomes, empirical HT use is suboptimal and not well-understood. The overall objective of this study was to assess associations between patient characteristics, physician characteristics, hospital characteristics, and community characteristics and use of hormone therapy operationalized as initiation, adherence, and persistence. A retrospective analysis of the Surveillance, Epidemiology, and End Results (SEER) registry linked with Medicare claims was conducted. The full study sample included older women diagnosed with hormone receptor-positive stage I-III breast cancer from 2010 through 2014. Initiation was defined as filling at least one prescription for HT. Adherence was defined as having proportion of days covered (PDC) of 0.80 or more in the first year. Persistence was defined as having no HT discontinuation, i.e., a break of at least 90 continuous days at any point during the study period. Length of persistence was calculated as time from therapy initiation to discontinuation. All analyses were conducted using SAS 9.4. An a priori alpha level of 0.05 was used to determine significance for all the analyses. ICC values were assessed to test for clustering at physician, hospital, and zip code level. A marginal model with clustering at zip code level was used to assess associations between study predictor variables and outcome variables. Logistic Regression models were constructed to assess associations between HT initiation and adherence and study predictors while Cox Proportional Hazards models were constructed to assess associations between HT persistence and study predictor variables. Final models were restricted to the patients who had non-missing provider data (15,014 patients for initiation, 9,949 patients for adherence/persistence). 65.46[64.93, 66.00] % of all candidates initiated HT, first year adherence rate was 76.77[76.17, 77.36] % and overall persistence rate was 64.24[63.55, 64.92]. Initiation of hormone therapy was associated with age, race, marital status, dual eligibility, tumor stage and HER2 status, physician specialty, hospital ownership, and zip code median education level; adherence to hormone therapy was associated with type of hormone therapy, medication switches, HER2 status of tumor, physician specialty, teaching hospital status and zip code median education level; and persistence with hormone therapy was associated with type of hormone therapy, medication switches, physician specialty, hospital physician count and urban/rural residence.