Impact of Blinding on Patient-Reported Outcome Differences Between Treatment Arms in Cancer Randomized Controlled Trials

Some concerns have been raised about potential bias in patient-reported outcome (PRO) results from open-label cancer randomized controlled trials (RCTs). We investigated if open-label trials favor the experimental treatment over the standard treatment more frequently than blinded trials. We also examined if the effect of blinding differs for distal vs more proximal PROs. We assessed 538 RCTs with a PRO endpoint conducted in the most prevalent cancers, of which 366 (68.0%) were open-label, 148 (27.5%) were blinded, and 24 (4.5%) were categorized as unclear. In our multivariable logistic regression model, we did not observe a statistically significant association of the independent variable treatment concealment (blinded vs open-label) on the dependent variable measuring the proportion of trials favoring the experimental treatment (adjusted odds ratio = 1.19, 95% confidence interval = 0.79 to 1.79; 2-sided P = .40). This was also the case when comparing distal and proximal PROs. Our findings provide novel evidence-based data that support the validity of PRO results from open-label cancer RCTs.