Up to 50% of Breast Cancer Survivors (BCS) do not take tamoxifen as prescribed, which increases the risk of recurrence and mortality. Few psychosocial predictors of non-adherence have been identified and no published studies have described interventions to improve tamoxifen adherence. The aims of this PhD were to examine barriers to tamoxifen adherence in BCS and to develop a psychoeducational intervention to improve adherence. To address limitations with previous research, this PhD used the Common Sense Model (CSM) and the Theory of Planned Behaviour (TPB) as a framework for investigating non-adherence. A systematic review found few consistent predictors of non-adherence and highlighted a need for more research on modifiable factors. A qualitative study showed that adherence was related to the beliefs patients hold about tamoxifen and how they weigh these beliefs up against their side effects (n=32). In a large questionnaire study (n=777), components from the CSM and the TPB explained between 17% and 46% of the variance in non-adherence. Unintentional non-adherence was reported more frequently than intentional non-adherence but was harder to explain. Women within their first year of treatment were sent follow up questionnaires at 3, 6 and 12 months (n=345). Reported rates of non-adherence increased significantly over time, as did perceived intensity of side effects. Results identified severable variables associated with non-adherence: ethnicity, employment status, necessity/concerns differential and perceived behavioural control. Both models provided excellent discrimination between adherent and non-adherent women. A psychoeducational self-management booklet was developed and was trialled in a small study, which supported the feasibility and acceptability of the intervention (n=41). Significant improvements were seen to variables associated with adherence, such as side effects, medication beliefs and self-efficacy for managing symptoms. The results from these studies highlight factors associated with tamoxifen non-adherence, which can be used clinically to identify patients at risk of non-adherence, and as the basis for interventions to improve adherence. Initial testing of a psychoeducational self-management intervention showed promising results. Combining constructs from both the CSM and the TPB provided the best understanding of non-adherence. Future research should apply this combined model to medication adherence in other conditions.
Investigating barriers to tamoxifen adherence in women with breast cancer
Moon, Z. E. (Author). 1 Oct 2017
Student thesis: Doctoral Thesis › Doctor of Philosophy