The term oligometastatic (OM) was introduced to describe patients with a limited number of clinically detectable metastases for which local ablative therapy could potentially provide improved disease-free survival or even cure. The incidence of an oligometastatic disease distribution is difficult to estimate. The purpose of this analysis was to describe the reasons precluding trial participation in our trial of SBRT for oligometastatic cancer. We retrospectively audited all patients who were screened for participation in a single-arm phase II trial designed for patients with OM cancer (up to 5 sites of extra-cranial metastases). Study participants received local ablative therapy to all known sites of disease and at least one index lesion was treated with 5 fraction SBRT (study intervention). Eligibility criteria required baseline computed tomography (CT) ≤1 month prior to enrolment, and all cases were discussed at peer-review rounds to confirm eligibility. Between Mar 7 2013 and Nov 17 2017, 236 patients were screened and 145 (61%) enrolled to the study. The reasons for screen failure included patients declining study participation in 4% (9/236) [n = 9; 4 with <5 mets, and 5 with uncertain number] and 12% (29/236) having >5 metastases upon restaging baseline scans. Of the remaining 53 patients who had ≤5 metastases but were not enrolled, reasons for screen failure included uncertainty that the primary tumor was controlled (n=9), lesions where alternative ablative therapy was recommended (n=10), not suitable for SBRT (n=18; size n=3, non-SBRT strategy preferred n=8, toxicity risk n=4, previous RT field overlap n=3), high subjective risk of systemic relapse (n=9; progressive disease during restaging scans n=4, not suitable for comprehensive ablative therapy n=1, plan for systemic therapy n=4) or other reasons (n=7; e.g. index lesion resolution, index lesion was a primary tumor, presence of cranial metastases). In our review of a cohort of patients flagged to be potential candidates for enrollment in a clinical trial of SBRT for OM cancer, 87% of patients were confirmed to have <5 metastases. The screen failure rate was high. The most common reason for exclusion was detection of >5 metastases (12%) while a small group of patients (5%) were deemed to be at high risk of systemic relapse based on clinical factors and peer review rounds. Reporting of the characteristics of screen failed patients are important in the interpretation of trial results.
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