A mixed methods investigation of the impact of insomnia on adherence to endocrine therapy treatment in patients with breast cancer

Agnew, Sommer

Thesis

A mixed methods investigation of the impact of insomnia on adherence to endocrine therapy treatment in patients with breast cancer

Download PDF

Creator

Agnew, Sommer

Rights statement

Strathclyde Thesis Copyright

Awarding institution

University of Strathclyde

Date of award

2026

Thesis identifier

T17626

Person Identifier (Local)

202184069

Qualification Level

Doctoral (Postgraduate)

Qualification Name

Doctor of Philosophy (PhD)

Department, School or Faculty

Department of Psychological Sciences and Health

Abstract

Approximately 70% of breast cancer cases are hormone receptor positive, therefore treatable with Endocrine Therapy (ET). When taken as prescribed, ET is effective in reducing the risk of breast cancer recurrence and mortality. However, research indicates that many patients struggle to take ET consistently. The most consistent, modifiable predictor of nonadherence to ET is treatment side effects. However, to date, research has not identified a specific side effect which consistently predicts nonadherence. This means we lack knowledge of potential targets for intervention to improve ET adherence. Insomnia is highly prevalent among patients with breast cancer (particularly those prescribed ET), and treatment of insomnia is known to have transdiagnostic benefits. Therefore, insomnia may be a sensible target symptom which, if treated, could reduce the overall burden of ET side effects and improve adherence. The aims of this thesis are 1) investigate the impact of side effects on intentional and unintentional nonadherence to ET, identifying potential targets for intervention to improve adherence, 2) investigate the effect of improved sleep on unintentional and intentional nonadherence to ET, and 3) explore the potential role of insomnia in nonadherence to ET and gain insight into patient perceptions of how improved sleep could potentially improve adherence. A cross-sectional survey study was conducted to explore the presentation of ET side effects in a large sample of patients with breast cancer (N=1051) prescribed ET. Using a data-driven approach, two symptom clusters emerged based on severity of all measured symptoms. Participants in the cluster with severe levels of all symptoms were significantly more likely to be both intentionally and unintentionally nonadherent to ET (based on self-reported measures). The symptom most frequently reaching clinical levels in the sample was insomnia, and insomnia was significantly correlated with severity of all other symptoms. To investigate the potential for improved sleep to improve ET adherence, a pilot randomised controlled trial was conducted of cognitive behavioural therapy for insomnia (CBT-I) in patients prescribed ET (N=32). Participants who received CBT-I reported a significantly greater improvement in unintentional nonadherence, depression, and musculoskeletal pain than the control group. A qualitative study using semi-structured interviews (N=21) was conducted to explore patient perspectives of the potential role of insomnia in nonadherence, and potential for improved sleep to improve adherence. Participants reported that insomnia affected their ability (unintentional nonadherence) and willingness (intentional nonadherence) to take ET consistently. Participants reported that, following CBT-I, they felt better able to remember to take their medication, and less inclined to deliberately miss doses due to perceived improvement in overall quality of life. This thesis provides a novel contribution to the literature and addresses key limitations of past research in this area. Overall, this thesis suggests that CBT-I may have transdiagnostic benefits for patients prescribed ET, which could potentially help to reduce intentional and unintentional nonadherence to ET, and provides direction for future research in this area.

Advisor / supervisor