Efficacy and Safety of Pembrolizumab (MK-3475) in Combination With Bacillus Calmette-Guerin (BCG) in High-Risk Non-Muscle Invasive Bladder Cancer (HR NMIBC) (MK-3475-676/KEYNOTE-676)

Inclusion Criteria: * Have locally and blinded independent central review (BICR)-confirmed histological diagnosis of high-risk non-muscle invasive (T1, high grade Ta and/or CIS) UC of the bladder * Has undergone cystoscopy/ transurethral resection of bladder tumor (TURBT) to remove all resectable disease * Has provided tissue for biomarker analysis * Has Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2 * Has adequate organ function * During the treatment period and for ≥7 days after the last dose of BCG, male participants are EITHER abstinent from heterosexual intercourse as their preferred and usual lifestyle and agree to remain abstinent, OR, must agree to use contraception unless confirmed to be azoospermic * Female participants who are not pregnant, not breastfeeding, and either not a woman of child bearing potential (WOCBP); or are a WOCBP who agrees to use a contraception method that is highly effective or remains abstinent from heterosexual intercourse during the treatment period and for ≥7 days after the last dose of BCG or 120 days after the last dose of pembrolizumab, whichever comes last BCG Post-induction Cohort (Cohort A) Only * Has been treated with one adequate course of BCG induction therapy for the treatment of HR NMIBC * Following adequate BCG induction therapy, must have persistent or recurrent HR NMIBC Exclusion Criteria: * Has a history of or concurrent locally advanced (i.e., T2, T3, T4) or metastatic UC * Has concurrent ext…