A Study of Pembrolizumab (MK-3475) in Relapsed or Refractory Classical Hodgkin's Lymphoma (rrcHL) or Relapsed or Refractory Primary Mediastinal Large B-cell Lymphoma (rrPMBCL) (MK-3475-B68)

Exclusion Criteria

• •Has undergone solid organ transplant at any time, or prior allogeneic hematopoietic SCT within the last 5 years
• •Has clinically significant (i.e., active) cardiovascular disease: cerebral vascular accident/stroke (\<6 months prior to enrollment), myocardial infarction (\<6 months prior to enrollment), unstable angina, congestive heart failure (New York Heart Association Classification Class ≥II), or serious cardiac arrhythmia requiring medication
• •Has pericardial effusion or clinically significant pleural effusion
• •Has a history of a second malignancy, unless potentially curative treatment has been completed with no evidence of malignancy for 2 years. Note: The time requirement does not apply to participants who underwent successful definitive resection of basal cell carcinoma of the skin, squamous cell carcinoma of the skin, superficial bladder cancer, in situ cervical cancer, or other in situ cancers
• •Is receiving systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) \<3 days prior to the first dose of study intervention. Note: Participants who receive daily steroid replacement therapy are an exception
• •Has received prior monoclonal antibody within 4 weeks prior to first dose of study intervention or has not recovered (i.e., ≤Grade 1 or at baseline) from adverse event (AEs) due to agents administered more than 4 weeks earlier
• •Has received prior therapy with an anti-programmed cell death 1 protein (PD-1), anti-programmed cell death ligand 1 (PD-L1), or anti-programmed cell death ligand 2 (PD-L2) agent or with an agent directed to another stimulatory or coinhibitory T-cell receptor (e.g., CTLA-4, OX-40, CD137)
• •Has received prior chimeric antigen receptor T-cell (CAR-T) therapy
• •Has received prior systemic anticancer therapy, or radiotherapy, including investigational agents within 4 weeks prior to the first dose of study intervention. Note: If the participant had a major operation, the participant must have recovered adequately from the procedure and/or any complications from the operation before starting study intervention
• •Has received prior radiotherapy within 2 weeks of start of study intervention or have had a history of radiation pneumonitis. Participants must have recovered from all radiation-related toxicities, and not require corticosteroids
• •Has received a live or live-attenuated vaccine within 30 days before the first dose of study drug
• •Is currently participating in or has participated in a study of an investigational agent or has used an investigational device within 4 weeks before the first dose of study intervention
• •Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 7 days prior to the first dose of study medication
• •Has known active central nervous system (CNS) lymphoma involvement or active CNS involvement by lymphoma
• •Has severe hypersensitivity (≥Grade 3) to pembrolizumab and/or any of its excipients
• •Has an active autoimmune disease that has required systemic treatment in past 2 years (i.e., with use of disease modifying agents, corticosteroids or immunosuppressive drugs). Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency) is not considered a form of systemic treatment and is allowed
• •Has a history of (noninfectious) pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease
• •Has an active infection requiring systemic therapy
• •Has a known history of human immunodeficiency virus (HIV) infection. No HIV testing is required unless mandated by local health authority
• •Has a known history of Hepatitis B (defined as hepatitis B surface antigen (HBsAg) reactive) or known active Hepatitis C virus infection