2522 - Stereotactic Body Radiation Therapy vs. Palliative Radiotherapy, with or without Immunotherapy, in Metastatic Bladder Cancer: A Canadian Population Analysis

E. Gutierrez¹, J. Graham², R. Breau³, P. C. Black⁴, N. Alimohamed⁵, W. Kassouf⁶, R. Agnihotram⁷, and P. Chung⁸; ¹IMSS, leon, Mexico, ²University of Manitoba, Manitoba, ON, Canada, ³Division of Urology, Department of Surgery, The Ottawa Hospital and University of Ottawa, Ottawa, ON, Canada, ⁴University of British Columbia, Kelowna, BC, Canada, ⁵Division of Medical Oncology, University of Calgary, Calgary, AB, Canada, ⁶McGill University Health Centre, Montreal, QC, Canada, ⁷Departement of Oncology, McGill University Health Centre Research Institute, Montréal, QC, Canada, ⁸Department of Radiation Oncology, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada

Purpose/Objective(s):

The integration of stereotactic body radiation therapy (SBRT) into the treatment paradigm of metastatic bladder cancer may represent a provocative approach. The SABR-COMET trial reported improved overall survival (OS) in oligometastatic patients treated with SBRT but the bladder cancer population was underrepresented. We report the clinical outcomes of patients with metastatic bladder cancer treated with SBRT in a Canadian population. Materials/

Methods:

From a prospectively collected database registered in the Canadian Bladder Cancer Information System, we identified patients with oligometastatic or oligoprogressive bladder cancer treated with SBRT = 5 Gy/fraction or palliative radiotherapy (PRT) defined as 6-8Gy in 1 fraction or 20Gy in 5 fractions to at least one metastatic index lesion from 2015 to 2024. Outcomes of interest were overall survival estimated using the Kaplan-Meier method and treatment-related adverse events (TAE)
Results: We identified 183 patients who received SBRT or PRT. Of these, 107 patients (58.5%) received PRT, with 89 PRT alone and 13 receiving PRT + immunotherapy. The most common locations treated were bone (62%), followed by soft tissue and lung (14%) and others (24%). The median follow-up time was 537 days (IQR=599) for SBRT and 503 days (IQR=568) for PRT. Overall survival (OS) at 24 months was 85.5% for SBRT versus 56% for PRT, [HR 0.64 (0.44–0.91) (P = 0.014)]. A sub-analysis of OS comparing SBRT alone versus SBRT + Immunotherapy showed no significant difference (P = 0.247). The incidence of TAE in the entire cohort was 5.46% for gastrointestinal and 1.9% for genitourinary events.
Conclusion: SBRT with or without immunotherapy appears to be associated with better OS compared to PRT (+/- immunotherapy), The rate of recorded adverse events was low overall. While there is likely a bias in selecting patients with better prognosis for SBRT, these findings warrant further investigation to establish a more comprehensive understanding of the role of SBRT and its clinical implications for this patient population. The interplay between SBRT and immunotherapy likewise needs further study given the known immunogenicity of the large dose/fraction normally employed in this setting.