S973
Clinical - Oligometastatic cancer
ESTRO 2026
Conclusion: With extended follow-up, SABR-5 continues to demonstrate a low incidence of high-grade toxicity and no new treatment-related deaths. These findings confirm the long-term safety of SABR delivered within a population-based, quality-assured program. As SABR-COMET-3 and -10 conclude and results mature, these data reinforce the value of continued accrual to disease-specific and histology-focused trials evaluating the role of SABR across diverse metastatic settings. References: Olson R, Jiang W, Liu M, Bergman A, Schellenberg D, Mou B, Alexandar A, Carolan H, Hsu F, Miller S, Atrchian S, Chan E, Ho C, Mohamed I, Lin A, Berrang T, Bang A, Chng N, Mattews Q, Baker S, Huang V, Mestrovic A, Hyde D, Lund C, Pai H, Valev B, Lefresne S, Tyldesley S. Treatment with stereotactic ablative radiotherapy for up to 5 oligometastases in patients with cancer: primary toxic effect results of the nonrandomized phase 2 SABR-5 clinical trial. JAMA Oncology 2022:8(11); 1644-50. Keywords: SABR, toxicity, oligometastases Prognostic Significance of New Versus Pre-Existing Lesions in Oligoprogressive Disease Treated with SABR. Curtis Leclerc 1 , Benjamnin Mou 2 , Mitchell Liu 3 , Will Jiang 4 , Devin Schellenberg 5 , Abraham Alexander 6 , David Petrik 2 , Howard Pai 6 , Islam Mohamed 2 , Chad Lund 4 , Jaime Kwok 4 , Haley Clark 7 , Scott Tyldesley 3 , Robert Olson 8 , Sarah Baker 4 1 Medicine, University of British Columbia, Vancouver, Canada. 2 Radiation Oncology, BC Cancer - Kelowna, Kelowna, Canada. 3 Radiation Oncology, BC Cancer - Vancouver, Vancouver, Canada. 4 Radiation Oncology, BC Cancer - Surrey, Surrey, Canada. 5 Radiation Oncology, BC Cancer - Surrey, Kelowna, Canada. 6 Radiation Oncology, BC Cancer - Victoria, Victoria, Canada. 7 Medical Physics, BC Cancer - Surrey, Surrey, Canada. 8 Radiation Oncology, BC Cancer - Prince George, Prince George, Canada Digital Poster 2370 Purpose/Objective: Oligoprogressive disease represents a unique presentation of metastatic cancer where stereotactic ablative radiotherapy (SABR) may be able to ablate resistant clones and prolong systemic control. However, oligoprogression may arise from either progression in pre-existing lesions or the emergence of new metastases, the latter scenario potentially reflecting a more disseminated presentation of resistant cancer cells. This study aimed to evaluate whether the presence of new metastases at baseline or recurrence predicts worse clinical outcomes
following SABR. Material/Methods:
Patients with oligoprogressive disease treated with SABR between November 2016 and April 2024 across British Columbia, Canada were retrospectively analyzed, including those enrolled in the phase II SABR-5 trial and the provincial Oligometastases Registry. Baseline, treatment, and tumor characteristics were extracted from clinical and imaging data. Lesions were categorized as new versus pre-existing metastases.Primary outcomes were progression-free survival (PFS), overall survival (OS), and polymetastatic progression-free survival (PPFS), assessed using Kaplan-Meier and multivariable Cox regression analyses. A total of 271 patients were included in the baseline analyses, and 221 patients who developed progression post-SABR were included in the recurrence analyses. Results: Median age was 69 years, and median follow-up was 39.4 months. The most common histologies were lung (21%), prostate (19%), and renal cell carcinoma (17%). 93% of patients had ≤ 2 metastases treated with SABR.At baseline, patients treated for new metastases (n=94) had significantly shorter PFS than those with pre-existing lesions (n=177) (6.8 vs 9.4 months, p=0.03). On multivariable analysis, new metastases independently predicted worse OS (HR 1.50, p=0.03), PFS (HR 1.43, p=0.02), and PPFS (HR 1.43, p=0.05) at baseline.
Following SABR, the emergence of new metastases was the dominant pattern of disease recurrence (73%). Among patients with recurrence, the emergence of new metastases was associated with shorter post- recurrence OS (28.4 vs 61.9 months, p<0.001) and post-recurrence PPFS (10.6 vs 25.5 months, p<0.001). On multivariable analysis, new metastases remained an independent predictor of worse OS (HR 2.29, p<0.001) and PPFS (HR 2.26, p<0.001).
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