Informing interventions to improve uptake of adjuvant endocrine therapy in women with breast cancer: a theoretical-based examination of modifiable influences on non-adherence

Purpose To inform intervention development, we measured the modifiable determinants of endocrine therapy (ET) non-adherence in women with breast cancer, using the Theoretical Domains Framework (TDF) and examined inter-relationships between these determinants and non-adherence using the Perceptions and Practicalities Approach (PAPA). Methods Women with stages I–III breast cancer prescribed ET were identified from the National Cancer Registry Ireland ( N = 2423) and invited to complete a questionnaire. A theoretically based model of non-adherence was developed using PAPA to examine inter-relationships between the 14 TDF domains of behaviour change and self-reported non-adherence. Structural equation modelling (SEM) was used to test the model. Results A total of 1606 women participated (response rate = 66%) of whom 395 (25%) were non-adherent. The final SEM with three mediating latent variables (LVs) (PAPA Perceptions: TDF domains, Beliefs about Capabilities, Beliefs about Consequences ; PAPA Practicalities: TDF domain, Memory, Attention, Decision Processes and Environment ) and four independent LVs (PAPA Perceptions: Illness intrusiveness; PAPA Practicalities: TDF domains, Knowledge, Behaviour Regulation ; PAPA External Factors: TDF domain, Social Identity ) explained 59% of the variance in non-adherence and had an acceptable fit ( χ 2 (334) = 1002, p < 0.001; RMSEA = 0.03; CFI = 0.96 and SRMR = 0.07) Knowledge had a significant mediating effect on non-adherence through Beliefs about Consequences and Beliefs about Capabilities . Illness intrusiveness had a significant mediating effect on non-adherence through Beliefs about Consequences . Beliefs about Consequences had a significant mediating effect on non-adherence through Memory, Attention, Decision Processesg and Environment . Conclusions By underpinning future interventions, this model has the potential to improve ET adherence and, hence, reduce recurrence and improve survival in breast cancer.