What is your preferred second-line agent for treatment of metastatic urothelial carcinoma?

And how should we compare checkpoint inhibitors? Given the FDA approval of atezolizumab and nivolumab as second-line agents for metastatic urothelial carcinoma (based on results from single-arm studies) and the recently reported positive data on pembrolizumab (based on the randomized phase III KEYNOTE-045), there are now at least two and potentially more immune checkpoint inhibitor options for patients with metastatic urothelial cancer.