EXTEND Trial Supports MDT in Oligometastatic Disease : J Clin Oncol | May 2026

Introduction

The concept of oligometastatic disease proposes that selected patients with limited metastatic burden may benefit from aggressive local treatment directed at metastatic sites in addition to systemic therapy. Metastasis-Directed Therapy, most commonly stereotactic radiotherapy, has demonstrated promising outcomes in several tumor-specific studies, but whether its benefit extends consistently across multiple solid tumor histologies has remained uncertain. The phase II EXTEND trial evaluated the addition of MDT to standard systemic therapy across several oligometastatic solid tumor “baskets.”

Problem Statement

Although prior studies suggested progression-free survival benefits with local ablative therapy in oligometastatic disease, most trials were small, histology-specific and underpowered for broad oncologic applicability. Reliable biomarkers defining true oligometastatic biology and predictors of MDT responsiveness also remain lacking.

Summary

The multicenter randomized phase II EXTEND trial enrolled patients with one to five metastatic lesions across six tumor-histology baskets including pancreatic, breast, renal and prostate cancers. Patients were randomized to receive standard systemic therapy alone or combined with metastasis-directed therapy, predominantly stereotactic radiotherapy. After a median follow-up exceeding four years, the addition of MDT significantly improved progression-free survival across all baskets combined. Importantly, this benefit persisted even after exclusion of prostate cancer cohorts, addressing concerns that highly radiosensitive prostate disease might disproportionately drive positive results.

Histology-specific analyses demonstrated particularly strong efficacy signals in pancreatic cancer, prostate cancer and the heterogeneous “Other” basket, whereas breast and kidney cancer cohorts yielded less definitive results. These findings support the possibility that oligometastatic biology and sensitivity to local ablative therapy vary substantially according to tumor histology.

The study also provided important translational insights. Detectable circulating tumor DNA (ctDNA) at baseline correlated with inferior progression-free and overall survival, whereas ctDNA clearance three months after treatment was associated with improved outcomes. These findings suggest that molecular residual disease assessment may help refine future definitions of oligometastatic disease and identify patients most likely to benefit from aggressive local therapy.

Additionally, immune profiling demonstrated enhanced systemic immune activation among patients receiving MDT combined with systemic therapy, particularly within tumor baskets showing the greatest clinical benefit. These observations reinforce the hypothesis that focal radiotherapy may augment systemic antitumor immunity through immunomodulatory and abscopal mechanisms rather than merely improving local disease control.

Overall, the EXTEND trial provides one of the strongest multicancer randomized datasets supporting incorporation of metastasis-directed therapy into management strategies for selected oligometastatic solid tumors. The findings support future phase III validation studies and highlight ctDNA-guided stratification and immune activation as important future directions in precision oligometastatic oncology.