OBJECTIVES: Unblinded trials are common in oncology, but patient knowledge of treatment assignment may bias response to questionnaires. We sought to ascertain the extent of possible bias arising from patient knowledge of treatment assignment.
METHODS: This is a retrospective analysis of data from 2 randomized trials in multiple myeloma, 1 double-blind and 1 open label. We compared changes in patient reports of symptoms, function, and health status from prerandomization (screening) to baseline (pretreatment but postrandomization) across control and investigational arms in the 2 trials. Changes from prerandomization scores at ~2 and 6 months on treatment were evaluated only across control arms to avoid comparisons between 2 different experimental drugs. All scores were on 0- to 100-point scales. Inverse probability weighting, entropy balancing, and multiple imputation using propensity score splines were used to compare score changes across similar groups of patients.
RESULTS: Minimal changes from screening were seen at baseline in all arms. In the control arm, mean changes of <7 points were seen for all domains at 2 and 6 months. The effect of unblinding at 6 months in social function was a decline of less than 6 points (weighting: -3.09; 95% confidence interval -8.41 to 2.23; balancing: -4.55; 95% confidence interval -9.86 to 0.76; imputation: -5.34; 95% confidence interval -10.64 to -0.04).
CONCLUSION: In this analysis, we did not find evidence to suggest that there was a meaningful differential effect on how patients reported their symptoms, function or health status after knowing their treatment assignment.