Background: It is still unclear whether industrial funding of clinical trials might have an impact on results and conclusions. However, little information exists on the reporting of authors' conflicts of interests (COIs) for systematic reviews (SRs) and meta-analyses. Member journals of the International Committee of Medical Journal Editors (ICMJE) have an obligatory form for authors to declare potential COIs.
Objectives: To examine the presence of authors' COIs in SRs related to cancer which have been published in high-impact medical journals or the Cochrane library.
Methods:Based on an a priori protocol we performed a search in MEDLINE for cancer-related SRs published in 10 medical journals with the highest impact factors (e.g. NEJM, Lancet, etc.) between 2012/01 and 2016/12. In addition, we identified all cancer-related Cochrane reviews from the same period using the Cancer filter in the Cochrane Database of Systematic Reviews. Two review authors extracted information on COIs and content of the SR, in duplicate and independently.
Results: We identified 178 high-impact SRs and 356 Cochrane reviews, which met our inclusion criteria. A median of 8 authors (IQR 6-14) were involved in high-impact SRs and a median of 5 (IQR 4-6) in Cochrane reviews. Fifty-five (31%) SRs in high-impact journals have been published by at least 1 potentially conflicted author, 18 SRs (10%) in these journals did not give any information regarding personal COIs. Only 31 (9%) of the Cochrane reviews involved at least 1 potentially conflicted author. The median number of conflicted authors was 3 (IQR 2-7) in high-impact journals and 1 (IQR 1-2) in Cochrane reviews. Considering the first authors, 17 (10%) of the high-impact journals and 7 (2%) of Cochrane reviews reported potentially COIs conflicted.
Conclusion: Potential COIs are present in a large number of SRs related to cancer. Although the ICMJE requires reporting of COIs, not all high-impact medical journals report potential COIs of involved authors. There is an important need for further research on the effects of COIs, particularly on the influence on review results and conclusions.