Stereotactic body radiotherapy for bone-only oligometastatic bladder Cancer: a multi-institutional experience

Purpose To evaluate clinical outcomes, patterns of failure, local control (LC), and time to next systemic therapy (TTNT) in patients with bone-only oligometastatic bladder cancer treated with stereotactic body radiotherapy (SBRT). Materials and Methods We retrospectively analyzed 26 patients with 41 bone metastases treated with SBRT between 2012 and 2020 across four institutions. All patients had ≤3 bone metastases and received metastasis-directed therapy to all lesions. Overall survival (OS), progression-free survival (PFS), TTNT, and LC were estimated using the Kaplan–Meier method. Results After a median follow-up of 97.8 months, median OS was 8.9 months, with 1- and 2-year OS rates of 38.5% and 22.4%, respectively. Median PFS was 5.8 months, with 1- and 2-year PFS rates of 29.4% and 25.2%, respectively. Median TTNT was 4.4 months, and only 19.8% of patients remained free from systemic therapy at 1 year. Disease progression occurred in 46.2% of patients and was predominantly distant metastasis. In contrast, LC was excellent, with 1- and 2-year rates of 94.7% and 88.0%, respectively. No grade ≥ 3 toxicities were observed. Conclusion SBRT achieved excellent LC with minimal toxicity. However, systemic progression remained common. These findings suggest that prospective studies are needed to determine the role of SBRT within multimodal treatment strategies for bone-only oligometastatic bladder cancer.