Optimism Bias in the Design of Phase III Randomized Control Trials Evaluating PD-1/PD-L1 Targeting Monoclonal Antibodies

BACKGROUND: Many randomized control trials (RCTs) evaluating programmed death receptor-1 (PD-1)/programmed death ligand-1 (PD-L1) targeting monoclonal antibodies (mAbs) have been completed or are in progress. We examined hypothesized hazard ratios (HHRs) and observed hazard ratios (OHRs) from published RCTs evaluating these mAbs. METHODS: Publications of RCTs evaluating at least one PD-1/PD-L1 targeting mAbs approved by the US Food and Drug Administration were identified through PubMed searches. The primary reports of RCTs were retrieved. Two investigators extracted HHR, OHR for the primary endpoint among other data elements independently. The differences (∆HR) in HHR and OHR were analyzed statistically. A separate search was conducted for secondary reports after longer follow-ups, the updated OHR was extracted. RESULTS: Forty-nine RCTs enrolling 36 867 patients were included. The mean HHR and OHR were 0.672 and 0.738 respectively. The mean ∆HR was 0.067 (range: –0.300 to 0.895; 95% confidence interval (CI), 0.003-0.130). HHR was met or exceeded in 22 (45%) RCTs. OHR was ≥ 1.0 in 6 RCTs (12%). PD-L1 expression was not associated with the magnitude of effect. Of 18 RCTs with follow-up reports, the magnitude of benefit decreased in 8 RCTs with extended follow-ups. CONCLUSION: The majority of published RCTs evaluating PD-1/PD-L1 targeting mAbs did not achieve their hypothesized magnitude of benefit. The optimism bias requires attention from the cancer clinical research community given the number of these agents in development and the intense interest in evaluating these agents in a variety of disease settings.