Safety and Efficacy of Pembrolizumab (MK-3475) in Children and Young Adults With Classical Hodgkin Lymphoma (MK-3475-667/KEYNOTE-667)

Group 1 will consist of low-risk participants with cHL Stages IA, IB and IIA without bulky
disease. Group 2 will consist of high-risk participants with cHL Stages IIEB, IIIEA, IIIEB,
IIIB, IVA and IVB.

Inclusion Criteria:

- Group 1: Must have newly diagnosed, pathologically confirmed cHL at Stages IA, IB and
IIA without bulky disease. Group 2: Must have newly diagnosed, pathologically
confirmed cHL at Stages IIEB, IIIEA,IIIEB, IIIB, IVA and IVB

- Has measurable disease per investigator assessment

- Male participants must agree to use approved contraception during the treatment period
and for at least 120 days (or longer, if required by the drug label of chemotherapy
received by the participant on study) after the last dose of study treatment and
refrain from donating sperm during this period

- Female participants who are not pregnant or breastfeeding, and who are either not a
woman of childbearing potential (WOCBP), or are a WOCBP who agrees to use approved
contraception during the treatment period and for at least 120 days (or longer, if
required by the drug label of chemotherapy received by the participant on study) after
the last dose of study treatment

- Performance status: Lansky Play-Performance Scale ≥50 for children up to and including
16 years of age OR Karnofsky score ≥50 for participants >16 years of age

- Has adequate organ function

Exclusion Criteria:

- Has undergone solid organ transplant at any time, or prior allogeneic hematopoietic
stem cell transplantation within the last 5 years

- WOCBP who has a positive urine pregnancy test within 72 hours before the first dose of
study treatment

- Baseline left ventricular ejection fraction value <50% or shortening fraction of <27%

- Has received prior therapy with an anti-Programmed Death (PD)-1, anti-Programmed
Death-Ligand 1 (PD-L1), or anti-PD-L2 agent or with an agent directed to another
co-inhibitory T-cell receptor or has previously participated in a Merck pembrolizumab
(MK-3475) clinical study

- Has received any prior anti-cancer therapy, monoclonal antibody, chemotherapy, or an
investigational agent or device before the first dose of study treatment, or has not
recovered from AEs due to previously administered agents

- Has received a live vaccine within 30 days prior to the first dose of pembrolizumab

- Is currently participating in or has participated in a study of an investigational
agent or has used an investigational device within 4 weeks prior to the first dose of
study treatment

- Has a diagnosis of lymphocyte-predominant Hodgkin Lymphoma (HL)

- Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy
or any other form of immunosuppressive therapy within 7 days prior to the first dose
of pembrolizumab

- Has a known additional malignancy that is progressing or requires active treatment

- Has radiographically detectable central nervous system metastases and/or carcinomatous
meningitis as assessed by local site investigator at the time of diagnosis

- Has severe hypersensitivity (≥Grade 3) to any study therapies including any excipients

- Has an active autoimmune disease that has required systemic treatment in past 2 years

- Has a history of (non-infectious) pneumonitis that required steroids or has current
pneumonitis

- Has an active infection requiring systemic therapy

- Has a known history of human immunodeficiency virus (HIV) infection

- Has a known history of Hepatitis B or known active Hepatitis C virus infection

- Has a known history of active tuberculosis

- Has a history or current evidence of any condition, therapy, or laboratory abnormality
that might confound the results of the study, interfere with the participant's
participation for the full duration of the study, or is not in the best interest of
the participant to participate, in the opinion of the treating investigator

- Has known psychiatric or substance abuse disorders that would interfere with
cooperating with the requirements of the study

- Is pregnant or breastfeeding or expecting to conceive or father children within the
projected duration of the trial, starting with the screening visit through 120 days
(or longer, if required by the drug label of chemotherapy received by the participant
on study) after the last dose of trial treatment