Risk-Benefit of Phase 2 Monotherapy Trials in Adult Solid Cancers: A Systematic Review and Meta-Analysis.

Phase 2 (and phase 1 dose expansion, which we label phase 2 for the purposes of this study) cancer trials are the first direct tests of a new drug's efficacy. Because efficacy evidence is lacking, the therapeutic status of drug administration during ethical review is uncertain. We compared the efficacy and safety of cancer monotherapies in phase 2 with phase 3, where clinical equipoise underwrites a therapeutic status for drug administration. In this systematic review and meta-analysis, we searched Clinicaltrials.gov for phase 2 and 3 investigational monotherapy drug trials in six solid malignancies, with primary completion dates 2015-2020, inclusive. Two independent reviewers completed data extraction. Effects were estimated using an inverse-variance weighted random-effects model meta-analysis of proportions using the R package meta. We analyzed 130 phase 2 and 52 phase 3 trial arms, enrolling 6665 and 18,694 patients. The pooled objective response rate was 7% (95% CI 5%-11%) in phase 2 versus 24% in phase 3 (95% CI 17%-31%; p < 0.0001). The median PFS and OS were shorter in phase 2 compared to phase 3 (3.23 vs. 5.43 months, p < 0.0001; 9.46 vs. 14.44 months, p = 0.0001). The pooled rate of drug-related grade 3-4 adverse events was 30% (95% CI 23%-37%) in phase 2 and 25% (95% CI 19%-32%) in phase 3. Monotherapies delivered in phase 2 cancer trials present diminished risk-benefit compared with phase 3 and align with historic estimates for phase 1. Though there may be exceptions, risks for drug administration in phase 2 should generally be justified by appeals to research rather than therapeutic value.