Introduction: Patient-reported outcomes (PROs) are increasingly included within cancer clinical trials. If appropriately collected, analysed and transparently reported these data might provide invaluable evidence to inform patient care. However there is mounting indication the design and reporting of PRO data in cancer trials may be suboptimal. This programme of research will establish via three interlinked studies whether these findings are applicable to UK cancer trials, and if so, how to best enhance the way PROs are assessed, managed and reported in clinical trials. This study will explore with key stakeholders factors that influence optimal PRO protocol content, implementation and reporting; and make recommendations for training and guidance.

Methods and analysis: Semi-structured interviews will be conducted with members of key stakeholder groups. The purposive sample of up to 48 participants will include: (1) trial Chief Investigators, trial management group (TMG) members, statisticians and research nurses (RNs) of cancer trials including primary or secondary PRO, recruited via the National Cancer Research Institute (NCRI) Clinical Studies Group and Consumer Liaison Group and the UK Clinical Research Collaboration Registered UK Clinical Trial Unit (UKCRC-UKCTU) Network; (2) NCRI CLG members; (3) international experts in PRO oncology trial design and (4) journal editors and funding bodies. Data will be analysed using directed thematic analysis employing a coding frame and modified as analysis progresses. Formal triangulation of coding and member checking will be employed to enhance credibility.

Ethics and dissemination: This study was approved by the University of Birmingham Ethics Committee (Ref: ERN_17-0085). Findings will be disseminated via conference presentations, peer-review journals, patient groups and social media (@CPROR_UoB; http://www.birmingham.ac.uk/cpror).

Strengths and limitations • This novel study will capture perspectives on the barriers and enablers of optimal PRO practice from a comprehensive range of stakeholders with experience of PRO data collection and reporting. • The semi-structured interview format ensures a replicable process while allowing sufficient freedom to explore new and emerging concepts. • The recruitment strategy involves seeking participants through networks occupied by EPiC Senior Management Group members. However, any limitation to sample representativeness and diversity will be mediated through the use of other recruitment avenues including the authorship lists of the protocols/publications included in Phase I. • Study is at risk of self-selection and social-desirability bias. Participants are likely to take part if they have a pre-existing interest in PROs specifically and when recounting their experiences and insights are likely to wish to portray themselves in a positive manner due to the nature of this study.