Co-development of a text messaging intervention to support adherence to adjuvant endocrine therapy in women with breast cancer: A mixed-methods approach (Preprint)

BACKGROUND Adjuvant endocrine therapy (AET) reduces breast cancer recurrence and mortality in women with early-stage breast cancer. Unintentional nonadherence to AET is common (e.g., forgetting to take medication). Forming habits surrounding medication-taking could reduce reliance on memory and improve AET adherence. Short Message Service (SMS) text messaging interventions may offer a low-cost approach for promoting medication-taking habits. To optimize the likely effectiveness of such SMS text messages, the content should be developed using a transparent approach to ensure fidelity to relevant psychological theory, and with user input to increase acceptability. OBJECTIVE We aimed to develop a pool of brief SMS text messages promoting habit formation to support AET adherence, which are acceptable to women with breast cancer and show fidelity to theory-based behavior change techniques (BCTs). METHODS Based on published literature, we selected six BCTs derived from the habit formation model: Action Planning, Habit Formation, Restructuring the Physical Environment, Adding Objects to the Environment, Prompts/Cues, and Self-monitoring of Behavior. In Study 1, behavior change experts (n=10) created messages, each based on one of the six BCTs, in an online workshop and rated the fidelity of the messages to the intended BCT. In Study 2, women with experience of taking AET discussed the acceptability of the messages in a focus group (n=5), and messages were refined following this. In Study 3, women with breast cancer rated the acceptability of each message in an online survey (n=60). In Study 4, additional behavior change experts rated the fidelity of the remaining messages to the intended BCT in an online survey (n=12). Finally, a consultant pharmacist reviewed a selection of the messages to ensure the messages did not contradict general medical advice. RESULTS In Study 1, 189 messages were created targeting the six BCTs. Ninety-two messages were removed due to being repetitious, unsuitable, or over 160 characters and 3 were removed due to low fidelity (scoring <5.5/10 on a fidelity rating scale). Following Study 2, we removed 13 messages considered unacceptable to our target population. In Study 3, all remaining messages scored above the midpoint on an acceptability scale (1-5), so none were removed (mean=3.9/5 [SD 0.9]). Following Study 4, we removed 13 messages due to low fidelity (scoring <5.5/10 on a fidelity rating scale). All remaining messages showed fidelity to intended BCTs (mean=7.9/10 [SD 1.3]). Following the pharmacist review, 2 messages were removed, and 3 were amended, resulting in a pool of 66 messages. CONCLUSIONS We developed a pool of 66 brief SMS text messages targeting habit formation BCTs to support AET adherence. The messages showed acceptability to women with breast cancer and fidelity to intended BCTs. The delivery of the messages will be further evaluated to assess their effect on medication adherence.