Atezolizumab Immunotherapy, in Immunotherapy Naive Patients With Urinary Tract Squamous Cell Carcinoma (UTSCC).

Treatment will consist of atezolizumab, by IV infusion, at a fixed dose of 1680 mg, every 28 days (day 1 of each cycle, +/- 3 days), for up to one year. Each participant will receive up to 13 doses in total.