Validation of metastasis-free survival as a surrogate endpoint for overall survival in localized prostate cancer in the era of docetaxel for castration-resistant prostate cancer

Operationalizing intermediate clinical endpoints: A pragmatic framework for prostate cancer management trials

Despite therapeutic advances, prostate cancer remains lethal for most patients. Accelerated development of novel therapies requires validated surrogate endpoints to circumvent prolonged survival follow-up in phase III trials. This review systematically evaluates intermediate clinical endpoints (ICEs) in prostate cancer to establish methodologically robust alternatives to overall survival (OS). We first synthesized methodological standards for ICE validation. Subsequent analysis encompassed phase III trials (PubMed/Web of Science, Jan. 2025) in metastatic castration-sensitive (mCSPC) and -resistant prostate cancer (mCRPC), requiring: randomization, therapeutic intervention, OS as primary/co-primary endpoint, ≥1 ICE (radiographic progression-free survival (rPFS), milestone survival), and ≥70 participants. Surrogacy was quantified via two-stage meta-analysis, with R2 ≥ 0.7 defining validity. Metastasis-free survival (MFS) is validated for localized disease, enabling trial endpoint substitution. In advanced stages, evidence for ICEs remains critically deficient. Our analysis identifies milestone survival as a promising ICE candidate in mCSPC and mCRPC, demonstrating strong trial-level correlation with OS. Current ICE validation in prostate cancer is disproportionately focused on localized disease, leaving advanced-stage therapeutic development constrained. While milestone survival shows surrogacy potential, endpoint validation remains methodologically challenging even in rigorously designed trials. This work underscores the imperative to accelerate ICE standardization through unified methodological frameworks and collaborative cross-trial analyses.

The State of Intermediate Clinical Endpoints as Surrogates for Overall Survival in Prostate Cancer in 2024

In the past, selection of intermediate clinical endpoints (ICEs) in prostate cancer (PCa) trials largely depended on qualitative assessments; however, the advancing quality of research necessitates a robust correlation with overall survival (OS). This review summarises the results from several high-quality meta-analyses that explored the validity of ICEs as surrogates for OS. We found strong evidence that metastasis-free survival can serve as an ICE in localized PCa. In advanced disease, valid ICEs were identified only within the context of metastatic hormone-sensitive PCa, including radiological and clinical progression-free survival; however, concerns remain regarding their use owing to the limited generalisability of the data used to validate their surrogacy. PATIENT SUMMARY: Intermediate clinical endpoints can reduce the costs of trials and allow earlier introduction of new treatment methods. This article summarises results from studies verifying the validity of these endpoints as surrogates for overall survival.

Improvement of assessment in surrogate endpoint and safety outcome of single-arm trials for anticancer drugs

INTRODUCTION

Single-arm trials (SATs) and surrogate endpoints were adopted as pivotal evidence for accelerated approval of anticancer drugs for more than 30 years. However, concerns regarding clinical evidence quality in trials, particularly in the SATs of anticancer drugs have increasingly been raised. SAT may not always provide strong evidence due to the lack of control and endpoint of overall survival that is typically present in randomized controlled trials.

AREAS COVERED

Clinical trial endpoint adjudication is a crucial factor in surrogate outcome measurement to ensure the data quality of the clinical trial of anticancer drugs. In this review, we systematically discuss the characteristics of adjudications in assessments in surrogate endpoint and safety outcome respectively, which are essential for ensuring reliable and transparent outcomes. Endpoint adjudication effectively reduces potential bias and mitigates variance that may be introduced by investigators when analyzing the medical records for the surrogate endpoints. We analyze the advantages and disadvantages of each type of adjudicator and provide a summary of the roles of adjudicators.

EXPERT OPINION

By suggestion of improving data reliability and transparency in pivotal trials, this review aims to supply a strategy for better clinical investigation for anticancer drugs, ultimately leading to better patient outcomes.