Acceptability, fidelity and trial experience of four intervention components to support medication adherence in women with breast cancer: A process evaluation protocol for a pilot fractional factorial trial

Background: Adjuvant endocrine therapy (AET) reduces mortality risk in early-stage breast cancer, but adherence is low. We developed a multicomponent intervention to support AET adherence comprising: text messages; information leaflet; acceptance and commitment therapy (ACT); side-effect management website. Guided by the multiphase optimization strategy, the intervention components were tested in the ROSETA pilot optimization trial. Our mixed-methods process evaluation investigated component acceptability. Methods: The pilot optimization trial used a 24-1 fractional factorial design. Fifty-two women with breast cancer prescribed AET were randomized to one of eight experimental conditions, each containing a unique combination of components. An acceptability questionnaire was administered four months post-randomization, and semi-structured interviews with 20 participants further explored acceptability. Assessments were guided by four domains of the theoretical framework of acceptability; affective attitude, burden, perceived effectiveness, and coherence. Quantitative and qualitative findings were triangulated to identify agreements/disagreements. Results: There were high overall acceptability scores across components (median=14-15/20, range=11-20). Overall there was agreement between the qualitative and quantitative findings when triangulated. Most participants ‘liked’ or ‘strongly liked’ all components, and reported they generally required low effort to engage in. Perceived effectiveness was mixed, with 35.0% (text messages) to 55.6% (ACT) of participants ‘agreeing’ or ‘strongly agreeing’ that each component would improve their adherence. Interview data provided suggestions to improve acceptability. Conclusion: The four components were acceptable to women with breast cancer, and will be refined prior to a full optimization trial. Mixed-methods and triangulation were useful methodological approaches and could be applied in other optimization trial process evaluations.