How can a remotely delivered, personalised physical activity intervention for people with high risk of breast, lung and bowel cancer recurrence be implemented in England? Protocol for a mixed-methods process evaluation embedded in a feasibility basket trial

Introduction Randomised controlled trials (RCTs) are essential to determine intervention effectiveness yet they often fail to capture how and why interventions succeed or fail in different contexts. Embedding a process evaluation alongside a clinical trial allows exploration of implementation processes, intervention fidelity and contextual influences.

The CANFit trial is a basket-design RCT evaluating a personalised, remotely delivered exercise intervention for people diagnosed with breast, lung and bowel cancer with increased risk of recurrence. This embedded process evaluation aims to understand how individual, team and organisational factors influence intervention delivery and uptake.

Methods and analysis A concurrent, mixed-methods process evaluation will be conducted using a hybrid type 1 design. Data will be collected from multiple sources, including participant and trainer questionnaires, semi-structured interviews, intervention adherence logs, trainer diaries and observations.

Five core implementation outcomes, guided by Proctor's framework - acceptability, appropriateness, fidelity, penetration and sustainability - will structure the evaluation. Quantitative data will be analysed descriptively and qualitative data will undergo framework analysis using both deductive and inductive coding.

Data integration will occur through a convergent mixed-methods approach, using context-mechanism-outcome (CMO) configurations to refine programme theory. Ethics and dissemination Ethical approvals were obtained through Hull York Medical School (ID: 23/SS/0060) and the UK NHS Health Research Authority (ID: 327663).

All participants will provide informed consent before taking part. Data will be handled according to General Data Protection Regulation and University of Hull data management policies.

Findings will be disseminated through peer-reviewed publications, conference presentations, stakeholder reports and lay summaries for participants and the public. Trial registration number ISRCTN97662203 .