Purpose: We sought to determine the prevalence, reliability, and predictors of conflict of interest (COI) and funding disclosure statements for studies of anticancer targeted therapies conducted in the off-label prescribing setting.
Methods: As a part of a federally funded systematic review, manuscripts were included in the analysis if they were used to support one of 19 indications for cancer targeted therapies that were off-label but reimbursable according to compendia published in 2006 or before. Studies were categorized according to trial design, trial results, average impact factor of journals, and presence of COI and funding disclosure statements.
Results: Among the 69 included studies, prevalence of COI and funding disclosures was low, at 33% and 58% respectively; time trends showed some improvement between 2002 to 2007, but only 60% of studies had disclosures by 2007. Predictors of COI disclosure were publication in high-impact-factor journals (P < .001), large study sample size (P = .001), enrollment exclusively in the United States (P = .04), and study of the targeted therapy in combination with other agents as opposed to the study drug alone (P = .03).
Conclusion: Disclosure of potential sources of bias in COI and funding statements in studies of off-label indications for anticancer targeted therapies was low and did not increase substantially over time.