A Phase 3, Randomized, Double-blind Study to Evaluate Perioperative Pembrolizumab (MK-3475) + Neoadjuvant Chemotherapy versus Perioperative Placebo + Neoadjuvant Chemotherapy in Cisplatin-eligible Participants with Muscle-invasive Bladder Cancer (KEYNOTE-866)

Inclusion Criteria: - Have a histologically confirmed diagnosis of urothelial carcinoma (UC) / muscle invasive bladder cancer (MIBC) (T2-T4aN0M0 or T1-T4aN1M0) with predominant (≥50%) urothelial histology. - Have clinically non-metastatic bladder cancer (N≤1 M0) determined by imaging (computed tomography (CT) or magnetic resonance imaging (MRI) of the chest/abdomen/pelvis - Be deemed eligible for Radical Cystectomy (RC) + Pelvic Lymph Node Dissection (PLND) - Have Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1 - Have adequate organ function. - Male and female participants are eligible to participate if they agree to the contraception use as per study protocol. Exclusion Criteria: - Has a known additional malignancy that is progressing or has required active anti-cancer treatment ≤3 years of study randomization with certain exceptions - Has received any prior systemic treatment for MIBC or non-invasive muscle bladder cancer (NMIBC - prior treatment for NMIBC with intravesical BCG/chemotherapy is permitted) or prior therapy with an anti- programmed cell death 1 (PD-1), anti-programmed cell death ligand 1/ ligand 2 (PD-L1/L2), or anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) - Has ≥N2 disease or metastatic disease (M1) as identified by imaging - Is cisplatin-ineligible, as defined by meeting any one of the cisplatin ineligibility criteria as per protocol - Has received prior systemic anticancer therapy including investigational agents within 3 years of randomization or any radiotherapy to the bladder - Has undergone partial cystectomy of the bladder to remove any NMIBC or MIBC - Has received a live or live attenuated vaccine within 30 days before the first dose of study intervention - Has a diagnosis of immunodeficiency or has a known history of human immunodeficiency virus (HIV) infection, Hepatitis B infection or known active Hepatitis C infection - Has a known psychiatric or substance abuse disorder - Has had an allogenic tissue/solid organ transplant