PCN268 ASSOCIATION BETWEEN ADHERENCE TO ORAL HORMONE THERAPY AND TYPE OF ORAL HORMONE THERAPY IN MEDICARE BENEFICIARIES WITH HORMONE RECEPTOR POSITIVE BREAST CANCER

Abstract

Use of oral hormone therapy for hormone receptor positive breast cancer has increased and newer aromatase inhibitor drugs have been incorporated into therapy. However, there is limited data on adherence to oral hormone therapy, or on any differences among drug classes in adherence. The objectives of this study were to 1) determine levels of adherence to oral hormone therapy for breast cancer in the Medicare population, and 2) assess association between hormone therapy type and adherence. Data used were from 2010-2014 SEER-Medicare files. Inclusion criteria were female sex, diagnosis of hormone receptor positive breast cancer, and at least 2 Medicare Part D claims for tamoxifen or aromatase inhibitors. Exclusion criteria were not being continuously enrolled in Medicare. Claim-based medication adherence was calculated as proportion of days covered (PDC) in a one-year period following start of oral hormone therapy. Individuals with PDCs of 0.80 or higher were considered adherent. Multivariate logistic regression was used to assess associations between hormone therapy type and adherence, after controlling for patient demographic characteristics (age, race, income, insurance and marital status). Among 19,200 individuals who met selection criteria, 16,340 (85.1%) took aromatase inhibitors and 2,860 (14.9%) took tamoxifen. The overall proportion (95% confidence interval) of adherent patients was 76.3%, (75.2% - 78.1%). Adherent proportion among aromatase inhibitor users was 78.3%, (77.7% - 78.9%), while 64.7%, (62.9% - 66.4%) of tamoxifen users were adherent to their medication. Age, race, household income, insurance type, and marital-status were not significantly associated with adherence. Based on multivariate logistic regression, patients on an aromatase inhibitor were 1.9 times (1.8-2.1) more likely to be adherent than patients on tamoxifen (p<0.0001), after controlling for age, race, household income, insurance, and marital-status. Women with hormone receptor positive breast cancer were 1.9 times more likely to be adherent to aromatase inhibitors as compared to tamoxifen.