Patients with T2-T4a N0 urothelial bladder carcinoma (UBC) with residual disease after transurethral resection of the bladder (TURB, surgical opinion, cystoscopy or radiological presence) will receive 3 cycles of pembrolizumab (MK-3475) at the dose of 200mg 3 weekly prior to surgery (radical cystectomy). Cystectomy will be planned to be done within 3 weeks of the last dose (accounting for a total of 9 weeks).