Would you consider a trial of pembrolizumab in a patient with metastatic urothelial carcinoma progressing on atezolizumab?

I dont think that would make sense. The monotherapy data for all the CPI are very similar. IMvigor 211 was a negative trial purely on a "trial design" issue. The ITT population was positive favoring atezolizumab over chemotherapy. I would consider a CPI after a trial of chemotherapy or radiation which may alter the tumor micro environment

Agree with @Dr. First Last on approach, however, there may be some theoretical advantage (as yet to be clinically proven) of using an anti-PD1 over anti-PD-L1, as there could be suppression mediated through PD-1 via expression of PD-L2 in the TME (reviewed: https://www.hindawi.com/journals/jir/2012/656340/). Thus, switching to an anti-PD-1 may add some benefit.

Combination immunotherapy trial would be first choice, obviously....but out side of that, I would switch mechanisms initially using chem...