Standardizing Trial Endpoints for Oligometastatic Cancer Therapy: The Lancet Oncology

Introduction

Oligometastatic cancer represents an intermediate disease state characterized by limited metastatic burden and a potentially distinct therapeutic window for metastases-directed therapy (MDT). As MDT becomes increasingly integrated into oncologic care, defining meaningful and consistent clinical trial endpoints has become essential to accurately assess treatment benefit and guide future therapeutic strategies.

Problem Statement

Clinical trials evaluating MDT in oligometastatic cancer have used highly variable primary endpoints, limiting cross-trial comparability and complicating interpretation of clinical benefit. Traditional endpoints such as overall survival and progression-free survival remain widely used, but they may not fully capture the unique therapeutic intent of MDT, particularly in settings where repeat local therapy can delay systemic progression without constituting treatment failure.

Summary

This review and Delphi consensus from the EORTC–ESTRO OligoCare consortium proposes a standardized framework for primary endpoints in clinical trials of MDT for oligometastatic cancer. Based on a systematic review of 121 comparative trials and a structured international consensus process involving experts and patient representatives, overall survival emerged as the preferred primary endpoint, reflecting its enduring clinical relevance. However, the panel emphasized that overall survival alone may not adequately capture the distinct benefits of MDT. In addition to progression-free survival, two alternative endpoints reached strong consensus: polymetastatic progression-free survival and systemic therapy-free survival. These endpoints are particularly valuable in MDT-based strategies because they allow repeat local interventions without prematurely defining treatment failure and better reflect the goal of delaying widespread progression or escalation of systemic treatment. Patient representatives also identified preservation of quality of life, particularly time to quality-of-life deterioration, as a major priority. This consensus provides a more clinically meaningful and patient-centered framework for future MDT trials and is expected to improve study design, comparability and translational relevance across oligometastatic oncology.