Abstract P1-09-01: The effect of generic anastrozole on adherence to adjuvant endocrine therapy
Authors: Neuner JM , Kamaraju S , Smith E , Charlson J , Smallwood A , Laud P , Pezzin L 
Published: August 2014

Background: Endocrine therapies, particularly aromatase inhibitors, substantially reduce breast cancer mortality in clinical trials. High rates of cost-related nonadherence to these long-term oral medications, however, have reduced their population-wide impact. While the 2006 Medicare Part D introduction promised to improve this situation, most Part D enrollees’ out-of pocket aromatase inhibitor costs actually remained high and rose steadily over subsequent years. We examined the effect of a natural experiment which lowered these costs—anastrozole patent expiration—upon endocrine therapy adherence among a nationwide sample of breast cancer patients.

Methods:Our sample included all female Medicare beneficiaries aged &gt; = 66 identified (using a validated Medicare claims algorithm) as having incident breast cancer surgery in 2006-07 who also had one or more Part D claim for an aromatase inhibitor or tamoxifen between 7/1-12/30/2008. Part D claims were used to calculate adherence, defined as medication possession ratio (MPR)&gt;80%, and medication out-of-pocket costs. A binary outcome regression model with a logit link was estimated using generalized estimating equations to study the effect of FDA approval of generic anastrozole (7/1/2010) upon adherence. The model was also adjusted for patient sociodemographic and health characteristics (age, race, comorbidities), time since surgery, low-income subsidy (LIS) (which lowers copays and eliminates the Medicare D “donut hole”) and temporal trend.

Results: The mean out-of-pocket medication cost for the 22,203 cohort members (85% white, 47% age &gt; = 75, 31% low income subsidy recipients, 45% anastrozole users) was $205 in the first quarter of 2009. Cohort members’ adherence to endocrine therapies dropped 15.8% from 72% in the first quarter to 61% in the last quarter during the pre-generic year (2009). In contrast, adherence was reduced by less than half that amount (-6.3%) between the same time periods in 2010 once anastrozole went generic. In adjusted models, both generic anastrozole availability and receipt of a low income subsidy were strongly associated with greater adherence to hormonal therapy (table). White race, younger age, and lower comorbidity all had smaller but statistically significant associations with greater adherence. There were no significant interactions between variables.

Adherence to Adjuvant Endocrine Therapy with Availability of Generic AnastrozoleFactorOdds Ratio95 CIP valueGeneric Anastrozole2.642.38 to 2.94.001Low Income Subsidy1.961.76 to 2.20.001also adjusted for year, quarter of year, comorbidity, race, age

Conclusions and Implications: The introduction of generic anastrozole was associated with a substantial and clinically significant improvement in endocrine therapy adherence among Medicare Part D enrollees. Such results have generally not been observed in studies of generic medications for chronic diseases, and may partly reflect increasing out-of-pocket demands by insurers. These findings, along with our findings of better adherence among low income subsidy recipients, highlight the importance of regulatory and subsidy policies for patients requiring long-term cancer medications.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-09-01.