Development and Preliminary Validation of a Tool to Assess Barriers and Facilitators to Participation in Adjuvant Endocrine Therapy Switch Trials.

Improving accrual to clinical trials is critical in oncology, particularly in studies evaluating treatment de-escalation or modification strategies, such as endocrine therapy (ET) switch trials in breast cancer. In disease-free patients who have completed an initial period of standard adjuvant ET, decision-making is shaped by individual, clinical, and contextual factors that may act as barriers and facilitators to trial participation. The lack of validated instruments complicates the comprehensive evaluation of these determinants. Therefore, our study aimed to develop and validate a scale for measuring barriers and facilitators to clinical trial participation in adjuvant endocrine therapy switch trials (CAMBRIA-1 and EMBER-4) among breast cancer patients. Therefore, a multiphase study was undertaken: phase one focused on item generation through literature review and expert consensus; phase two assessed preliminary validity through content and face validation (S-CVI and CVR) and pre-testing (Cronbach's alpha). The final scale encompassed 17 items and exhibited strong evidence of face and content validity (S-CVI = 0.78 and CVR > 0.725 for all items) and internal consistency (Cronbach's alpha = 0.874). Since preliminary internal consistency has been established, this tool may support future psychometric refinement and large-scale investigations. An understanding of these determinants may inform trial enrolment and drug development in breast cancer management, as well as tailor patient engagement strategies.