Anti-androgen prescribing patterns, patient treatment adherence and influencing factors; results from the nationwide PCBaSe Sweden.

PURPOSE: Adherence has not been studied in male oncology populations. The aim of this study on both the prescriber and user perspectives in prostate cancer treatment was to analyse real-life prescribing patterns of anti-androgens (AA), primarily bicalutamide, and factors influencing the patients' adherence to treatment.
METHODS: A nationwide clinical cohort of incident prostate cancer, PCBaSe, was linked to the Swedish Prescribed Drug Register. Men with a planned first line monotherapy AA treatment were identified; dosages and extent of off-label treatment were investigated. Cumulative incidence proportions for reasons for drug discontinuation were calculated. Factors potentially influencing adherence were explored using the medical possession ratio based on the individual prescribed daily dose.
RESULTS: First line monotherapy AA was planned in 4.4 % of all incident cases and in 2.1 % of low risk disease cases. Among 1,406 men prescribed bicalutamide, 1,109 (79 %) received the approved daily dose of 150 mg. Discontinuation reasons differed with disease severity. Off-label, low-dose prescription associated with age above 75 years and disease categorised as low risk was noted in 297 men (21 %). Sixty percent of the men adhered well, i.e. to ≥80 %. Age above 75 years and less severe disease were both negatively associated with adherence.
CONCLUSIONS: Patient age and tumour risk group influenced the prescriber's choice of dose, pointing to important issues for critical reflection. Possible over-treatment was noted in low risk disease. Interventions to increase adherence in older men and in men with less severe disease are worth considering after critically reviewing the appropriateness of the treatment indication, especially in the latter case.