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)

Inclusion Criteria:

• Have a histologically confirmed diagnosis of urothelial carcinoma (UC) / muscleinvasive 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 thechest/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 thecontraception use as per study protocol.

Exclusion Criteria:

• Has a known additional malignancy that is progressing or has required activeanti-cancer treatment ≤3 years of study randomization with certain exceptions.

• Has received any prior systemic treatment for MIBC or non-invasive muscle bladdercancer (NMIBC - prior treatment for NMIBC with intravesical BCG/chemotherapy ispermitted) 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-cytotoxicT-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 cisplatinineligibility criteria as per protocol.

• Has received prior systemic anticancer therapy including investigational agentswithin 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 doseof study intervention.

• Has a diagnosis of immunodeficiency or has a known history of human immunodeficiencyvirus (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.