Facilitating adherence to endocrine therapy in breast cancer: stability and predictive power of treatment expectations in a 2-year prospective study

To identify modifiable factors predictive of long-term adherence to adjuvant endocrine therapy (AET). As part of a 2-year cohort study in primary care (n = 116), we investigated whether initial treatment expectations predict adherence at 24 months after controlling for demographic, medical, and psychosocial variables. Treatment expectations were measured as necessity-concern beliefs, expected side-effect severity, and expected coping with side effects. Their stability over time and differences of trajectories between the adherent and nonadherent group were examined. Nonadherence at 24 months was 14.7% (n = 17). Side-effect severity at 3 months [OR 0.25, 95% CI (0.08, 0.81), p = 0.02] and necessity-concern beliefs [OR 2.03, 95% CI (1.11, 3.72), p = 0.02] were the sole predictors of adherence. Necessity-concern beliefs remained stable over 2 years, whereas expected side-effect severity (p = 0.01, eta (2)(p) = 0.07) and expected coping with side effects became less optimistic over time (p < 0.001, eta (2)(p) = 0.19), the latter particularly among nonadherers (p < 0.01, eta (2)(p) = 0.10). Patients' initial necessity-concern beliefs about the AET and early severity of side effects affect long-term adherence. Expecting poor management of side effects may also facilitate nonadherence. We suggest that discussing benefits, addressing concerns of AET, and providing side-effect coping strategies could constitute a feasible and promising option to improve adherence in clinical practice.