Perioperative Pembrolizumab (MK-3475) Plus Neoadjuvant Chemotherapy Versus Perioperative Placebo Plus Neoadjuvant Chemotherapy for Cisplatin-eligible Muscle-invasive Bladder Cancer (MIBC) (MK-3475-866/KEYNOTE-866)

A global study to evaluate peri-operative pembrolizumab with chemotherapy versus placebo to pembrolizumab plus chemotherapy in cisplatin eligible patients.

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.