Metastasis-directed radiotherapy in oligometastatic bladder and upper tract cancer: A single institution retrospective experience.

799 Background: Metastasis-directed therapy (MDT) for oligometastatic cancer is a concept utilized for prostate and kidney cancer. Clinical research in MDT for oligometastatic urothelial carcinoma (UC) remains sparse especially in the modern era where systemic therapy advancements have substantially improved patient’s outcomes overall. We explored our institutional experience of patients with oligometastatic carcinoma of the bladder and upper tract undergoing MDT utilizing radiotherapy (RT). Methods: Patients were retrospectively identified with oligometastatic bladder or upper tract cancer from January 2016 to July 2024 with five or less sites of metastases. Those with equivalent dose of RT (EQD2 10 ) ≥ 45Gy to metastases were included. Progression free survival (PFS) and overall survival (OS) were evaluated using Kaplan Meier from time of diagnosis to metastatic disease. Cox proportional hazards analysis was conducted to determine covariates associated with survival endpoints. Results: 60 patients with oligometastasis were included with 8 patients excluded due to a RT dose EQD2 10 < 45Gy. 52 patients were in final analysis. Most were men (67%) with a median age 68 years (range, 35-91). Most had bladder primary (79%) with the remaining including upper tract. Majority had pure UC (85%) and the remainder were UC subtypes with variant histology including small cell (8%), squamous (6%), sarcomatoid (2%). Median number of metastases was 1 site, while 23% had 3+ sites. Bony metastases (27%) were most common site, then retroperitoneal nodes (18%) and lung (17%). Most received ≥2 systemic therapy cycles before MDT (62%) with 8% without any therapy prior to MDT. Most commonly used therapy included ddMVAC (21%), Gem/Cis (20%), pembrolizumab (15%), and EV (12%). MDT was delivered to all metastases in 71%, while the remaining had MDT to select sites. Most common MDT dose was 30Gy in 3 fractions (21%) followed by 50Gy in 4 fractions (17%). Median follow up from metastatic diagnosis was 19 months (range, 3-106 months). Median PFS and OS was 21 months (95% CI 8-33 months), and 39 months (95% CI, 14-64 months), respectively. At last follow up, 31 patients were alive (60%). Most common first recurrence was distant from site of MDT (96%) while 2 patients had in-field recurrence in pelvic bones. On univariate analysis, those with 1 vs 2+ sites had improved PFS with MDT (p=0.03, 95% CI 1.1-6.0). Univariate showed no association with MDT to all sites vs select, age, or # lines of systemic therapy. Conclusions: As systemic therapy has improved for patients with bladder and upper tract cancers, MDT may serve as an effective adjunct to improve cancer control. Baseline characteristics. Characteristic (n=52) No % Median Age (yrs) 68 Histology UC 44 85% UC subtype with variant histology 7 15% Site of Primary Bladder 41 79% Upper Tract 11 21% Lines of therapy before MDT 0 4 8% 1 17 33% 2+ 31 60%