Do early phase trials predict clinical efficacy in subsequent phase III biomarker-enriched randomized trials?

3152 Background: Efficacy endpoints of randomized controlled trials (RCT) are commonly used as the basis of regulatory drug approvals. Recently, promising results in early phase trials have resulted in approval of biomarker-targeted therapies. We examined if early phase trial results were associated with efficacy in subsequent biomarker-enriched RCTs. Methods: All cancer drug RCTs conducted between January 2006 and March 2021 were identified through Clinicaltrials.gov. Trials were eligible if a biomarker was used to select a patient population for treatment with a targeted agent. Associated early phase trials were included if they matched the RCT in treatment setting and patient population. Trials pairs were compared using objective response rate (ORR) and progression-free survival (PFS). We assessed difference in endpoints using summary measures (e.g., average, range). We examined whether early phase trials results were associated with RCT results using logistic regression. Results: The search yielded 2,157 unique phase III RCTs and 27 RCTs met eligibility criteria pairing with associated early phase trials, where 17 RCTs met their primary endpoint. The most common biomarkers were EGFR+ (n = 8), HER2+ (n = 5) and PD-L1 (n = 5). Based on average difference of trial pairs, ORR was similar between trials (1.59%, 95% CI = -2.5-5.6, p = 0.50) and median PFS was slightly higher in early phase trials (1.95 months, 95% CI = 0.91-2.99, p < 0.05). On an individual pair basis, there was large range of variability in the difference between early phase trials and RCTs for ORR (range = -23.9-20.2%) and median PFS (range = -0.8-7.4 months). The probability of the RCT meeting its primary endpoint is 50% or 95%, when the early phase trial ORR is 41.2% (95% CI = 35.2-47.1%) or 77.7% (95% CI = 71.7-83.6%), respectively. Conclusions: Through comparison of early phase trials and subsequent phase III RCT, we found that, overall, ORR has minimal bias in early phase trials, and median PFS appears to be slightly overestimated. Substantial variability in results for trial pairs suggests that, on an individual basis, results in early phase trial can be inconsistent with results in subsequent RCT. Early phase trial results may be associated with RCTs meeting their primary endpoint when ORR is very high; however, caution must be exercised when using early phase trials as representative of RCTs for decision-making as the predictive ability of early phase trials is limited.

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