Influence of patient and treatment factors on adherence to adjuvant endocrine therapy in breast cancer.
To estimate the proportion of older women who fail to complete 5 years of tamoxifen therapy and to identify predictors of non-adherence. We followed 462 women 65-years-old or older with stage I–IIIA breast cancer diagnosed in four US regions between 1996 and 1999 and who initiated tamoxifen therapy. We interviewed patients annually to assess tamoxifen adherence and collected information about predictors of adherence by medical record review, patient interview, and physician questionnaire. Thirty-one percent of patients who started tamoxifen failed to complete the recommended 5-year course. Patients who had initial severe side effects [hazard ratio (HR) per side effect=1.2, 95% confidence interval (CI) 0.97, 1.5] or developed them (HR per new side effect=1.3, 95% CI 1.0, 1.6) were more likely to discontinue. Patients with more prescription medications at baseline were less likely to discontinue (HR per baseline prescription equaled 0.90, 95% CI 0.81, 0.99), whereas patients who added a prescription were more likely to discontinue (HR per new prescription equaled 1.2, 95% CI 1.0, 1.4). Patients with positive views of tamoxifen at baseline (HR for a 10-point higher score=0.93, 95% CI 0.83, 1.0) and an improving view over follow-up (HR for a 10-point positive change=0.93, 95% CI 0.87, 1.0) were less likely to discontinue. Five years of tamoxifen confers a significant benefit beyond 1–2 years of tamoxifen, so physicians should ask patients about side effects, other prescriptions, and beliefs about tamoxifen and should educate them about the benefits of completing adjuvant therapy.