Background: Publication bias (PB) can cause an exaggerated estimate of summary effects in systematic reviews (SR). The extent of PB assessment by SRs within oncology journals remains to be determined. Methods: This study looked at SRs from high impact factor oncology journals between 2007 and 2015 using a PubMed search. Articles were sorted and coded for PB. An additional assessment of BP from unevaluated SRs was performed using Egger’s regression and the trim-and-fill method. Findings: Of 182 included SRs, 52 preformed a PB assessment. The most common form of assessment was a funnel plot supplemented by Egger’s regression or Begg’s test (44%, 23/52). PB was a routine finding in these SRs (19%, 10/52). SRs that stated following a reporting guideline frequently failed to do so with regards to assessing PB. The magnitude of effect sizes generally decreased when conducting our independent assessments of PB among SRs in our sample that did not evaluate for it. Interpretation: Our study shows that there exists an underutilization of PB assessments by SRs in clinical oncology. Additionally the methodological validity of SRs can be increased by adhering to reporting guidelines, and through the search of grey literature and clinical trials registries. Funding: No external source of funding

Abstract Purpose: The purpose of this study was to evaluate the quality of reporting in the abstracts of oncology systematic reviews using PRISMA guidelines for abstract writing. Methods: Oncology systematic reviews and meta-analyses from four journals - The Lancet Oncology, Clinical Cancer Research, Cancer Research, and Journal of Clinical Oncology - were selected using a PubMed search. The resulting 337 abstracts were sorted for eligibility and 182 were coded based on a standardized abstraction manual constructed from the PRISMA criteria. Eligible systematic reviews were coded independently and later verified by a second coder, with disagreements handled by consensus. One hundred eighty-two abstracts comprised the final sample. Results: The number of included studies, information regarding main outcomes, and general interpretation of results were described in the majority of abstracts. In contrast, risk of bias or methodological quality appraisals, the strengths and limitations of evidence, funding sources, and registration information were rarely reported. By journal, the most notable difference was a higher percentage of funding sources reported in Lancet Oncology. No detectable upward trend was observed on mean abstract scores after publication of the PRISMA extension for abstracts. Conclusion: Overall, the reporting of essential information in oncology systematic review and meta-analysis abstracts is suboptimal and could be greatly improved. Keywords: Review, Systematic; Meta-Analysis; Cancer; Medical Oncology; Abstracting as Topic; Funding