Objectives: Although clinical trials have demonstrated the benefit of adjuvant hormonal therapy for hormone receptor-positive breast cancer, it is not known whether poor medication adherence might impact outcomes, particularly in the context of a low-income population traditionally underrepresented in clinical trials. We explored the relationship between adherence to tamoxifen or selective aromatase inhibitors with cancer recurrence and death in a low-income, Medicaid-insured population.
Methods: Using a Medicaid claims-tumor registry and National Death Index data, we evaluated adherence to adjuvant hormonal therapy [defined by the medication possession ratio (MPR)], cancer recurrence, and cancer-specific survival for female breast cancer diagnosed from 1998 to 2002, in North Carolina. Multivariate Cox proportional hazards models and logistic regression models were used to examine the role of adherence on cancer recurrence and survival.
Results: The sample consisted of 857 cases, mean age 67.7 years, 56.9% white, 60.9% local stage, with a mean follow-up of 4.4 years. Mean first-year MPR was 77%. MPR adherence was not significantly associated with cancer-related death [adjusted hazards ratio=1.18 (95% confidence interval, 0.54-2.59)], or recurrence [adjusted odds ratio=1.49 (95% confidence interval, 0.78-2.84)]. There was also no significant interaction between adherence and use of concurrent CYP2D6 enzyme inhibitors.
Discussion: Hormonal therapy adherence was not associated with breast cancer outcomes in this low-income population with relatively poor adherence. Although suboptimal adherence is considered to be an important clinical problem, its effects on breast cancer outcomes may be masked by patient genetic profiles, tumor characteristics, and behavioral factors.