A Study to Evaluate the Safety and Efficacy of Pembrolizumab (MK-3475) Coformulated With Berahyaluronidase Alfa (MK-3475A) in Participants With Relapsed or Refractory Classical Hodgkin Lymphoma (rrcHL) or Relapsed or Refractory Primary Mediastinal Large B-cell Lymphoma (rrPMBCL)(MK-3475A-F65)

Inclusion Criteria:

The main inclusion criteria include but are not limited to the following:

• Histologically confirmed diagnosis of classical Hodgkin lymphoma (cHL) or primarymediastinal B-cell lymphoma (PMBCL)

• Radiographically measurable cHL or PMBCL disease assessed by investigator as perLugano classification

• Have a life expectancy of >3 months

• Human immunodeficiency virus (HIV)-infected participants must have well controlledHIV on antiretroviral therapy (ART)

• Participants who are hepatitis B surface antigen (HBsAg) positive are eligible ifthey have received hepatitis B virus (HBV) antiviral therapy for at least 4 weeks,and have undetectable HBV viral load before enrollment

• Participants with history of hepatitis C virus (HCV) infection are eligible if theyhave completed curative antiviral therapy at least 4 weeks before enrollment and HCVviral load is undetectable at screening

• Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1assessed within 7 days before first dose of study intervention

Exclusion Criteria:

The main exclusion criteria include but are not limited to the following:

• Has clinically significant (i.e., active) cardiovascular disease

• Has pericardial effusion or clinically significant pleural effusion

• Has known additional malignancy that is progressing or has required active treatmentwithin the past 2 years

• Diagnosis of immunodeficiency or is receiving systemic steroid therapy or any otherform of immunosuppressive therapy within 7 days prior to the first dose of studyintervention

• Received prior monoclonal antibody within 4 weeks prior to first dose of studyintervention or has not recovered (i.e., ≤Grade 1 or at baseline) from adverseevents (AEs) due to agents administered more than 4 weeks earlier

• Received prior therapy with an anti-programmed cell death 1 protein (anti-PD-1),anti-programmed cell death ligand 1 (anti-PD-L1), or anti-programmed cell deathligand 2 (anti-PD-L2) agent, or with an agent directed to another stimulatory orcoinhibitory T-cell receptor

• Received prior systemic anticancer therapy including investigational agents within 4weeks before the first dose of study intervention

• Received prior radiotherapy within 2 weeks of start of study intervention, or hasradiation-related toxicities, requiring corticosteroids

• Received a live or live-attenuated vaccine within 30 days before first dose of studyintervention

• Is receiving systemic antineoplastic chemotherapy, immunotherapy, or biologicaltherapy not specified in this protocol

• Has known active central nervous system (CNS) metastases and/or carcinomatousmeningitis

• Active autoimmune disease that has required systemic treatment in the past 2 years

• History of (noninfectious) pneumonitis/interstitial lung disease that requiredsteroids or has current pneumonitis/interstitial lung disease

• Active infection requiring systemic therapy

• Concurrent active hepatitis B and hepatitis C virus infection

• Has undergone solid organ transplant at any time, or prior allogeneic hematopoieticstem cell transplant (SCT) within the last 5 years