A Tumor Growth Rate/Overall Survival Model For Atezolizumab As An Early Predictor Of Os In Patients With First Or Second Line Metastatic Urothelial Carcinoma.

62Background: Standard early endpoints are often poor predictors of overall survival (OS) for immunotherapies. There is a need for new intermediate endpoints to support upcoming combination studies with immune checkpoint inhibitors. We investigated the predictive performance of on-treatment tumor growth rate (TGR) estimates to predict OS in atezolizumab clinical trials in patients (pts) with metastatic urinary carcinoma (mUC). Methods: Atezolizumab showed durable response, prolonged OS and good tolerability supporting its therapeutic use in mUC (Rosenberg, Lancet 2016; Balar, lancet 2017; Powles, EACR-AACR-SIC 2017). A multivariate model linking baseline patient characteristics and TGR (estimated using time profile of sum of longest diameters (SLD) of target lesions, RECIST 1.1) to OS was developed using phase 2 data (IMvigor210) and validated to predict phase 3 trial (IMvigor211). Results: To estimate TGR, patients needed to have at least one post-baseline measurement: n = 365/429 (85%) in IMvigor210 (10...