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

Abstract

TPS543 Background: 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, RECIST 1.1 measurable disease, progression of disease after/on platinum-containing chemotherapy in the metastatic or perioperative setting, ECOG PS of 0-2 and adequate organ function. Twenty-two pts will be treated with Radium-223 at a dose of 55 kBq/kg IV and Atezolizumab 1200mg IV both on day 1 of 21 day cycles. Up to 6 doses of Radium-223 will be administered. Atezolizumab will be continued until lack of clinical benefit or intolerable toxicity for up to 17 cycles. Routine response assessment will be performed every 12 weeks. Primary endpoint is best overall response per RECIST 1.1. Secondary objectives are to determine the safety and tolerability; determine the overall survival, progression free survival, clinical benefit rate, complete response rate and duration of response; and changes in quality of life as assessed by the EORTC QLQ-C30 score. Exploratory objectives are PD-L1 status by IHC, changes in bone scan per EXINI bone scan index and efficacy measures by irRC. If ≥6 pts respond, corresponding to an ORR of 27% with 80% confidence limits of 15%-43%, further study of the combination would be warranted. Blood and archival tissue will be collected for correlative studies. Clinical trial information: NCT03208712.