BACKGROUND There is increasing concern that a significant proportion of randomised controlled trials (RCTs) included in Cochrane reviews may not be trustworthy. Applying a trustworthiness screening tool (TST) has already had a clinically important effect on several reviews published by the Cochrane Pregnancy and Childbirth Group. OBJECTIVES We wanted to assess the impact of removing untrustworthy RCTs from already- published Cochrane reviews on a defined clinical area (ante- and post-natal nutritional interventions). METHODS We applied the tool to 18 Cochrane reviews (375 RCTs). The tool had four domains: i) is the research governance trustworthy; ii) are the baseline characteristics trustworthy; iii) is the study feasible; iv) are the results plausible?). When additional information was needed, authors were contacted using a standard template. At least two attempts were made to contact the authors. At the end of the evaluation process each study was classified as: i) included (YES to all domains); ii) excluded (retracted study); or iii) awaiting classification (any NO to the TST questions). RESULTS 95/375 studies (25%) were removed, affecting 14/18 (78%) reviews. 13/18 reviews (72%) showed a difference in the Summary of Findings tables (direction and size of effects and/or GRADE ratings). 6/18 Cochrane reviews (33%) were judged to require updating because of important differences in either in their conclusions, implication for practice, and/or implication for research. CONCLUSIONS Formal assessment of trustworthiness and inclusion only of studies that satisfy prespecified criteria for trustworthiness affect conclusions in a relatively large number of Cochrane reviews, with potentially important clinical implications for practice and research. The lack of consensus regarding the best tool(s) for assessing trustworthiness cannot be an excuse for ignoring this issue in future Cochrane reviews.

Introduction Skin cancer affecting the nail unit is rare but is associated with morbidity, and melanoma has a high mortality rate. The principal treatment is surgical excision and methods can be classified into digit-sparing surgery or amputation. Digit-sparing surgery (wide excision or Mohs surgery) may be safe and effective for malignancies involving the nail unit in comparison to amputation if there is not bony invasion. The objective was to assess the efficacy and safety of different methods of surgical excision for skin cancer involving the nail unit. Methods Prospective comparative studies (randomised controlled, non-randomised controlled and prospective observational studies) of surgical excision for skin cancer of the nail unit in all participants were eligible for inclusion. We searched electronic databases, trials registers and conference abstracts. We checked the reference lists of included studies and related systematic reviews for further references to relevant studies, and we contacted experts to enquire if they were aware of any additional relevant trials. We used standard methodological procedures expected by Cochrane. The primary outcomes were overall survival, disease free survival and adverse events/outcomes at 30 days. The secondary outcomes were quality of life outcomes. We planned to use GRADE to assess the quality of the evidence for each outcome. Results We did not identify any studies that met the inclusion criteria for this review. We have been unable to assess our outcomes of overall survival, disease free survival, adverse events/effects and quality of life. Conclusions As we have not identified any studies for inclusion, we are unable to assess the efficacy and safety of different methods of surgical excision for skin cancer involving the nail unit. Prospective research, ideally in the form of a randomised trial, is required in this field. Registration Cochrane Database of Systematic Reviews 2021, Issue 5. Art. No.: CD014590.