Radium-223 and atezolizumab in platinum refractory urothelial carcinoma with bone metastases: NCT03208712.

TPS543Background: Immunologically, radiation increases tumor antigen release, cytotoxic CD8+ T cell infiltration while reducing myeloid derived suppressor cells (MDSCs), with distant abscopal responses occasionally reported. Radium-223 is a systemically administered bone-targeted alpha emitter that causes double-stranded DNA breaks and may induce similar immune effects. Anti-PD(L1) immune checkpoint inhibitor monotherapy with Atezolizumab demonstrates objective responses in metastatic urothelial cancer. In mouse models, radiotherapy and checkpoint immune inhibitor in combination synergistically reduce tumor growth. We hypothesized that the combination of Atezolizumab and Radium-223 in metastatic urothelial cancer pts with bone metastases would target bone metastases more effectively and yield higher response rates. Methods: Eligibility criteria for this single-site, phase 2 trial of Radium-223 in combination with Atezolizumab include diagnosis of advanced urothelial carcinoma with ≥1 bone metastasis, RECI...