OBJECTIVES : To explore the impact of the introduction of generic aromatase inhibitors (GAIs) on adjuvant hormone therapy (AHT) adherence among Medicare beneficiaries over the full recommended five-year course of breast cancer treatment.

METHODS : Using a sample of women aged >= 65 with hormone-receptor positive breast cancer from the SEER-Medicare-linked database, 2007 through mid-2009, interrupted time series model were conducted to predict the association between GAIs introduction and AHT adherence. The models were conducted for the full sample and also stratified by Medicare low-income subsidy (LIS) status.

RESULTS : Our study sample consists of 10,905 women with an average age of 76.9 years. The majority were white (83.6%), unmarried (60.1%), without comorbidity (34.7%), non-LIS (71.4%), and lived in metropolitan areas (81.2%). Among this sample of women, 62.8% initiated AI treatment within the first year of breast cancer diagnosis. Adjusted for sociodemographic characteristics, the sample overall demonstrated a decreasing trend in adherence (-0.036, p<0.001) before the introduction of GAIs. For the six months after the first GAI, anastrozole entered the market, there was a 3.2% increase in the slope (p<0.001), and for the six months after letrozole and exemestane entered the market, there was an additional 0.8% increase in the slope (p<0.001). Adherence among LIS beneficiaries was 11.0% higher than non-LIS beneficiaries (p<0.001), but the differences in adherence trends between LIS and non-LIS patients were small and statistically insignificant.

CONCLUSIONS : With the introduction of generic aromatase inhibitors, the decrease in breast cancer patients’ adherence attenuated over the course of their treatment. While the successful implementation of Medicare LIS program minimized the out-of-pocket costs for financially vulnerable patients, policymakers should be cautious about not to introducing disparities for those who may be low income but ineligible for such program.