More than just side-effects: The role of clinical and psychosocial factors in non-adherence to tamoxifen.

Abstract

Tamoxifen non-adherence is apparent in up to half of breast cancer survivors and is associated with increased risk of recurrence and reduced quality of life. However, factors contributing to non-adherence in this population are currently poorly understood. This study explored the relationship between key components of the Common Sense Model of Illness Representations (CSM)/the Theory of Planned Behaviour (TPB) and intentional and unintentional non-adherence in a large sample of women prescribed tamoxifen following primary breast cancer. Cross-sectional questionnaire study (n=777). Women were eligible if they were over 18, had been diagnosed with primary breast cancer, and had been prescribed tamoxifen. Participants were recruited in clinic or online and completed questionnaires assessing illness perceptions, treatment beliefs, adherence, quality of life, social support, distress, and the key TPB components. Logistic regressions were conducted to test elements from each model and to identify correlates of intentional and unintentional non-adherence. Patients were classified as non-adherent based on Medication Adherence Rating Scale scores; 44% of the population were non-adherent; 41% reported unintentional non-adherence, and 9% reported intentional non-adherence. Study variables accounted for more variance in intentional (Nagelkerke R2 =46%) than unintentional non-adherence (Nagelkerke R2 =17%). Intentional non-adherence was best explained by a combination of TPB and CSM variables, but these variables did not contribute significantly to unintentional non-adherence. The TPB and the CSM provide a useful framework for understanding intentional tamoxifen non-adherence. Elements from both models should be considered when designing interventions to increase adherence rates. Statement of contribution What is already known about this subject? Non-adherence to tamoxifen is common and is associated with poor clinical outcomes. Few modifiable predictors of tamoxifen non-adherence have been identified. What does this study add? Unintentional non-adherence is reported much more frequently than intentional non-adherence. Elements from the CSM and TPB provide a useful framework for understanding non-adherence to tamoxifen. Unique correlates were found for intentional and unintentional non-adherence.