KEY POINTS
- This multi-institutional retrospective study included 26 patients with 41 bone metastases from bladder cancer treated across four centres between 2012 and 2020. All had a controlled primary tumour, no nodal or visceral disease, and no more than three bone metastases, with every identified lesion treated using SBRT.
- Half of the patients had de novo oligometastatic disease, while 34.6% had oligorecurrent and 15.4% induced oligometastatic disease. A single metastasis was present in 57.7%, and the most frequent treated sites were the spine (53.7%) and pelvis (34.1%).
- Dose and fractionation were heterogeneous, ranging from 16–18 Gy in one fraction to 35 Gy in five fractions. Eighteen lesions (44%) received single-fraction treatment, and the median lesion-level biologically effective dose was approximately 48 Gy₁₀.
- Local control was high, reaching 94.7% at one year and 88.0% at two years. Only two of 41 lesions failed locally, and both failures occurred together with distant disease rather than as isolated in-field recurrence.
- Systemic control remained poor. Median progression-free survival was 5.8 months, with one- and two-year rates of 29.4% and 25.2%. Among the 12 patients who progressed, all developed distant metastases and ten developed polymetastatic disease.
- Median time to initiation or escalation of systemic treatment was only 4.4 months, and just 19.8% remained free from a new systemic treatment at one year. This endpoint was difficult to interpret uniformly because some patients were treatment-naive, whereas others were already receiving systemic therapy.
- Median overall survival was 8.9 months, with one- and two-year survival of 38.5% and 22.4%. No evaluated factor, including number of metastases, staging method, previous systemic therapy, or biologically effective dose, significantly predicted survival.
- Treatment was well tolerated: grade 2 pain flare occurred in 19.2% and grade 2 oesophagitis in 15.4%. No grade 3 or higher toxicity, vertebral compression fracture, pathological fracture, malignant cord compression, or clinically significant late toxicity was reported.
CLINICAL TAKEAWAY
SBRT can provide durable control of individual bone metastases from bladder cancer with little severe toxicity, but it should not be presented as adequate treatment on its own. The short interval to distant progression suggests that most patients require integration with effective contemporary systemic therapy, while better biomarkers are needed to identify the minority with genuinely indolent oligometastatic disease.