How Do Oncologists Globally Define Oligometastatic Disease? A Cross-Sectional Survey Study

Introduction: Oligometastatic disease (OMD) represents an intermediate state between localized and widely metastatic cancer. Despite major advances including the integration of metastasis directed therapy (MDT), SBRT/SABR, and improved imaging, there remains no universally accepted clinical definition of OMD. Existing consensus statements (e.g., EORTC, ESTRO, ASTRO) are predominantly developed in high-income countries, whereas oncologists in lower-resource settings may apply distinct criteria due to differences in diagnostic availability, disease burden, and therapeutic resources. Understanding real-world variations in OMD definitions is essential for harmonizing clinical practice, designing equitable trials, and improving patient selection for local ablative therapy.

The objective of this study is to evaluate how oncologists across different regions globally define oligometastatic disease and to identify patterns or discrepancies in diagnostic criteria, lesion cutoffs, and treatment intent.

Methodology: A cross-sectional, anonymous online questionnaire was distributed to practicing oncologists globally. The survey assessed definitions of OMD, classification by timing, imaging preferences, case-based scenarios interpretation, and management strategies. Data was reported as frequencies and percentages and analyzed using descriptive statistics.

Results: This is an ongoing study, and the data was collected through an online survey. This represents a pilot study (N=31), where 31 respondents have completed the survey, enrolled in various institutes across the globe. Google Forms was used to create the questionnaire, and the link was shared with participants via social media platforms. Most of the respondents were Radiation Oncologists, and 29% were Medical Oncologists, and the rest were surgical and clinical oncologists. Among these clinicians, 19 (61.3%) had access to stereotactic radiotherapy, while the rest did not. 17 (54.8%) respondents define oligometastatic disease as 1-5 lesions, and the rest define OMD as 1-3 lesions or they don’t have a fixed number. 22 respondents consider non-regional lymph nodes in the definition of OMD, while the rest do not. PET-CT scan was the preferred imaging modality among 19 (61.3%) participants, 4 (12.9%) preferred CT scan, and the rest describe that the imaging modality should depend on the site of the lesion. 24 (77.4%) participants chose 2 or more than 2 organ involvement for OMD. 19 (61.3%) respondents classify OMD independent of time, while 15 (48.4%) chose to describe synchronous OMD as metastasis detected at the time of initial cancer diagnosis. In the NSCLC case scenario 25 (80.6%) of the respondents classified the disease as oligometastatic and 5 (16.1%) considered it as poly-metastatic disease, among which the majority, 28 (90.3%), considered MDT with ablative intent for this patient. In the prostate cancer scenario, 24 (77.4%) questionees identified this state as oligo-progressive, while 7 classified it as OMD. 29 (93.5%) participants suggested SBRT to the lesion. Most of the oncologists, 22(71%), were of the view to treat OMD as curative, while 7 (22.6%) chose palliative intent to treat OMD. SBRT/SABR was the preferred local therapy among the majority, 20 (64.5%). 12 (38.7%) chose surgery, while the remaining wanted to treat OMD based on the site or with the consensus of the tumor board. Among the respondents, with or without access to SBRT, majority would treat OMD with curative intent (p = 0.301). Clinician specialty was significantly associated with inclusion of non-regional lymph node metastases in the definition of oligometastatic disease (p = 0.023) and with willingness to offer metastasis-directed local therapy in the presented clinical scenario (p = 0.041).

Conclusion: Oncologists differ greatly in their definitions, classifications, and approaches to oligometastatic disease management. These findings highlight the requirement of a universal consensus and underline the importance of standardized, evidence-based criteria to guide clinical practice and future trials.

Conflict of interests: The authors declare no conflict of interest.

Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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