Background
Consensus paper from European Society for Radiotherapy and Oncology (ESTRO) and EORTC. Systematic literature review and expert consensus exercise involving 29 international radiation oncologists to characterize, classify, and define oligometastatic disease (OMD) for clinical trial design and clinical practice. Aimed to establish a standardized framework for OMD research and treatment.
Interventions and follow up
Arm A: N/A — consensus classification exercise (no treatment randomization)
Primary endpoint: Consensus-based classification framework
mFollow up: N/A
Primary endpoint: Consensus-based classification framework
mFollow up: N/A
Results
Consensus outputs: OMD defined as ≤5 metastases, amenable to radical local treatment; sub-classified by history, timing, systemic therapy, and tumor biology
Definition adopted: Oligometastatic disease = ≤5 detectable metastases in ≤3 organs
Classifications: Synchronous OMD (at diagnosis) vs metachronous OMD (after treatment); induced OMD (after systemic therapy); repeat OMD
Recommended eligibility criteria: Good PS, controlled primary, lesions amenable to ablative RT, no prior OMD treatment within 6 months
Definition adopted: Oligometastatic disease = ≤5 detectable metastases in ≤3 organs
Classifications: Synchronous OMD (at diagnosis) vs metachronous OMD (after treatment); induced OMD (after systemic therapy); repeat OMD
Recommended eligibility criteria: Good PS, controlled primary, lesions amenable to ablative RT, no prior OMD treatment within 6 months
Adverse events
Main adverse events: N/A — consensus paper. Notes that ablative RT toxicity is site-dependent; risk-benefit assessment required for each metastatic site and patient.
Conclusions
Standardized definition and classification of OMD is essential for trial design consistency. The ≤5 metastases threshold in ≤3 organs is supported by biologic and clinical data. Metachronous OMD (arising after initial treatment) has a more favorable prognosis than synchronous OMD and may derive greater benefit from ablative treatment.
Key Limitations
Key Limitations: Expert consensus carries inherent bias from institution/specialty perspectives. The ≤5 threshold is arbitrary in the absence of randomized data proving its biologic significance. Definition does not incorporate molecular or imaging-based biomarkers that may better identify true oligometastatic disease biology.
Clinical Context
The ESTRO-EORTC consensus definition (≤5 metastases, ≤3 organs) is now widely used in clinical trials and practice for SBRT/SABR of oligometastatic disease. SABR-COMET, STOMP, ORIOLE, and major oligometastatic trials use this or similar definitions. Most NCCN guidelines for specific tumor types now incorporate OMD as a distinct category warranting consideration of local ablative therapy.
References