Objective: Comorbidity among breast cancer survivors is prevalent, and adherence to medication management of comorbidities may be important for both chronic disease and cancer-related outcomes. Our objective was to determine characteristics associated with nonadherence to common chronic medications among breast cancer survivors.
Methods: We conducted a retrospective cohort study of 4216 women in an integrated care system diagnosed with early-stage breast cancer between 1990 and 2008 and alive without recurrence or second primary breast cancer in the second-year following diagnosis. Adherence to antihypertensives, oral diabetes medications, and statins was measured during the second-year post-breast cancer diagnosis using medication possession ratios (MPR). Nonadherence was defined as MPR <0.80. We estimated odds ratios (OR) and 95% confidence intervals (CI) for nonadherence to antihypertensives, oral diabetes medications, and statins by various characteristics using multivariable logistic regression.
Results: Among 2308 users of antihypertensives (n = 1779), diabetes medications (n = 499) and/or statins (n = 1072), 37% were nonadherent to antihypertensives; 75% were nonadherent to diabetes medications; 39% were nonadherent to statins. In adjusted models, younger age was associated with nonadherence to all three therapeutic classes. Certain cancer treatments were associated with nonadherence to antihypertensives (radiation: OR 1.21, 95% CI 1.01-1.47; endocrine therapy: OR 1.27, 95% CI 1.03-1.52) and diabetes medications (chemotherapy: OR 1.69, 95% CI 1.17-2.21). Less frequent primary care provider visits were associated with higher odds of nonadherence to antihypertensives (OR 1.70, 95% CI 1.19-2.22); and trends showed higher Charlson comorbidity scores associated with greater adherence to diabetes medications (P < 0.001) and statins (P = 0.032).
Conclusions: Nonadherence to medications is high among breast cancer survivors, particularly diabetes medications, and is associated with cancer treatments and other patient characteristics. Additional research is warranted to understand the needs of cancer patients taking chronic medications and explore patient and provider factors influencing adherence.
Keywords: Breast cancer survivorship; Diabetes; Dyslipidemias; Hypertension; Medication adherence.