Blinded independent central review versus local investigator assessment of PFS in RCTs of immunotherapy in advanced cancers: A systematic review and meta-analysis

Background: Assessment of Progression-free survival (PFS) events by investigators might be inaccurate in randomized controlled trials (RCTs) with open-label design. We explored differences in PFS evaluated by blinded independent central review (BICR) or local investigator assessment (IA) in trials testing immunotherapy (IO) in advanced cancers.

Methods: We systematically reviewed articles of RCTs investigating IO in advanced tumors, published in PubMed-indexed journals up to December 2023. For each RCT, we collected PFS results by BICR and by local IA. We calculated the discrepancy index (DI) as the ratio of BICR and IA Hazard Ratios (HR_BICR/HR_IA) for PFS. An overall DI and relative confidence interval (CI) were calculated using a fixed-effect model weighted for the inverse of variance.

Findings: Only 32/140 (22.9 %) RCTs reported both BICR and local IA PFS data, including 17,054 patients. PFS was the sole primary endpoint in 19/32 (59.4 %) and a co-primary endpoint 9/32 (28.2 %) trials. The study design was open label or double-blind in 17/32 (53.1 %) and 15/32 (46.9 %) RCTs, respectively. The overall DI was 1.07 (95 % CI 1.01-1.13; I² =0, p = 0.02), revealing a more optimistic analysis of results in favor of local IA. In the 17 open-label trials, the overall DI was 1.09 (95 % CI 1.02-1.17, I2 =0, p = 0.02), revealing a more favorable interpretation of PFS results by local investigators.

Interpretation: We found a statistically significant difference between BICR and local IA of PFS in trials of IO in cancer. These results suggest that the double assessment is recommended in RCTs testing IO, especially in open-label trials.

Funding: This work was supported by the MFAG27826-2022 grant (Dr. Alberto Servetto).