Selective Outcome Reporting in Cancer Studies: A Scoping Review

Abstract Background Unbiased reporting of clinical study results is essential for evidence-based medicine. However, Selective Outcome Reporting (SOR) leads to Outcome Reporting Bias (ORB) and is prevalent across disease areas, including oncology. This scoping review aims to: (a) describe the current state of research on SOR in cancer studies, (b) assess the prevalence of SOR, (c) understand methods and definitions used in SOR assessment, (d) map available evidence and identify research gaps, and (e) discuss research and policy implications. Methods A systematic literature search was conducted using keywords related to endpoint discrepancies and oncology. Studies were screened, deduplicated, and evaluated. The JBI Critical Appraisal Checklist for Systematic Reviews and Research Synthesis was used for quality assessment. Results Six systematic reviews, each including 24 to 217 cancer clinical trials, were analysed. SOR prevalence varied from 4% to 79%, with a median rate of 12%. Definitions of endpoint discrepancies varied, complicating direct comparisons. SOR was identified as over-reporting, under-reporting, or misreporting outcomes. Conclusion SOR is a significant issue in oncology clinical trials, with implications for evidence synthesis, clinical practice, and policy. The lack of consistent definitions and detailed protocol reporting contributes to the challenge. Enhancing transparency and standardisation in outcome reporting could mitigate ORB and improve the reliability of clinical evidence. Implications: Future research should focus on consistent SOR definitions and improved protocol transparency. Policymakers and regulators should promote standards to reduce SOR and ensure transparent and trustworthy clinical trial outcomes.