RecruitingPhase 1/2

A Study of Pembrolizumab in Japanese Pediatric Participants With Solid Tumors or Lymphomas and Japanese Adult Participants With Merkel Cell Carcinoma (MK-3475-G21/KEYNOTE-G21)

Japan20 participantsStarted 2026-06-30

Plain-language summary

Researchers are looking for new ways to treat people with solid tumors, lymphomas (blood cancers), and a certain type of skin cancer. The goals of this study are to learn: * About the safety of pembrolizumab (the study medicine) and if people tolerate it * What happens to different doses of pembrolizumab in a person's body over time * How the cancer responds (gets smaller or goes away) to treatment

Who can participate

Age range

6 Months

Sex

ALL

See this in plain English?

AI-rewrites the medical criteria so a patient or caregiver can understand them. Always confirm with the trial site.

Inclusion Criteria: The main inclusion criteria include but are not limited to the following: Arm 1: * For participants with relapsed or refractory classical Hodgkin lymphoma (cHL) or primary mediastinal large B-cell lymphoma (PMBCL) * Has a confirmed diagnosis of relapsed or refractory cHL or PMBCL after the most recent therapy * Has radiographically measurable disease per Lugano classification * For participants with completely resected melanoma: * Has surgically completely resected and histologically/pathologically confirmed diagnosis of Stage IIB, IIC, III or IV cutaneous melanoma * Has not received any prior systemic therapy for their melanoma beyond surgical resection * All suspicious lesions amenable to biopsy are confirmed negative for malignancy * For participants with locally advanced or metastatic melanoma: * Has histologically confirmed diagnosis of locally advanced (unresectable Stage III) or metastatic (Stage IV) melanoma (including acral) not amenable to local therapy * Has radiographically measurable lesion(s) as defined by RECIST 1.1 * For participants with microsatellite instability-high (MSI-H)/mismatch repair deficiency (dMMR) solid tumors: * Has histologically/cytologically documented, locally-advanced, or metastatic solid malignancy that is incurable and has either (a) failed prior standard therapy, (b) for which no standard therapy exists, or (c) standard therapy is not considered appropriate by the participant and treating physic…

Questions worth asking your doctor

Bring these to your next appointment. They're a starting point for a shared conversation — not a sign you qualify or a recommendation to enrol.

1Based on my diagnosis and history, is this trial worth exploring for me — or is there a standard treatment we should try first?
2What does this trial's phase tell us about how much is already known about its safety and benefit?
3What would taking part actually involve for me — visits, tests, time, and travel?
4What are the known and possible risks or side effects I should weigh, and how would they be monitored?
5If this trial isn't the right fit, what other options or trials would you suggest I look into?

Generated to help you prepare — always confirm anything about your own eligibility and care with the study team and your doctor.

Questions for the trial coordinator

The trial coordinator is the person who runs the study day to day. These cover the practical side — logistics, costs, and what taking part would actually mean for your life. The study team confirms whether you meet the criteria; these are questions to ask, not a sign you qualify.

1What does taking part actually involve week to week — how many visits, where, and how long does each one take?
2What costs are covered by the study, and what might I have to pay for myself, including travel, parking, or time off work?
3What happens during screening, and what happens if the study team confirms I don't meet the criteria after those tests?
4Who pays for the scans, blood work, and other tests the trial requires — the study, my insurance, or me?
5How will being in the trial affect my regular care, and will my own doctor stay informed and involved?
6Can I leave the trial at any point if I change my mind, and what would happen to my care if I do?

A starting point for the conversation — always confirm anything about your own eligibility, costs, and care with the study team and your doctor.

What they're measuring

Arm 1: Number of Participants Who Experience an Adverse Event (AE)

Timeframe: Up to approximately 28 months

Arm 1: Number of Participants Who Discontinue Study Treatment Due To an AE

Timeframe: Up to approximately 25 months

Arm 1: Area Under the Concentration-Time Curve (AUC) of Pembrolizumab

Timeframe: Predose at Cycle 1, 2, 4, 8 and every 4 cycles thereafter up to 35 cycles; postdose at Cycle 1 and Cycle 8 (a cycle is 21 days)

Arm 1: Maximum Concentration (Cmax) of Pembrolizumab

Timeframe: Predose at Cycle 1, 2, 4, 8 and every 4 cycles thereafter up to 35 cycles; postdose at Cycle 1 and Cycle 8 (a cycle is 21 days)

Arm 1: Minimum Plasma Concentration (Cmin) of Pembrolizumab

Timeframe: Predose at Cycle 1, 2, 4, 8 and every 4 cycles thereafter up to 35 cycles; postdose at Cycle 1 and Cycle 8 (a cycle is 21 days)

Arm 2: Objective Response Rate (ORR) per Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) by Blinded Independent Central Review (BICR)

Timeframe: Up to approximately 37 months

Trial details

NCT IDNCT07302347

SponsorMerck Sharp & Dohme LLC

Sponsor typeINDUSTRY

Study typeINTERVENTIONAL

Primary completion2029-03-30

Contact for this trial

Toll Free Number

1-888-577-8839 Trialsites@msd.com

View on ClinicalTrials.gov More Malignant Neoplasm trials

Plain-language summary

Who can participate

Age range

6 Months

Sex

ALL

See this in plain English?

AI-rewrites the medical criteria so a patient or caregiver can understand them. Always confirm with the trial site.

What they're measuring

Arm 1: Number of Participants Who Experience an Adverse Event (AE)

Timeframe: Up to approximately 28 months

Arm 1: Number of Participants Who Discontinue Study Treatment Due To an AE

Timeframe: Up to approximately 25 months

Arm 1: Area Under the Concentration-Time Curve (AUC) of Pembrolizumab

Timeframe: Predose at Cycle 1, 2, 4, 8 and every 4 cycles thereafter up to 35 cycles; postdose at Cycle 1 and Cycle 8 (a cycle is 21 days)

Arm 1: Maximum Concentration (Cmax) of Pembrolizumab

Timeframe: Predose at Cycle 1, 2, 4, 8 and every 4 cycles thereafter up to 35 cycles; postdose at Cycle 1 and Cycle 8 (a cycle is 21 days)

Arm 1: Minimum Plasma Concentration (Cmin) of Pembrolizumab

Timeframe: Predose at Cycle 1, 2, 4, 8 and every 4 cycles thereafter up to 35 cycles; postdose at Cycle 1 and Cycle 8 (a cycle is 21 days)

Arm 2: Objective Response Rate (ORR) per Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) by Blinded Independent Central Review (BICR)

Timeframe: Up to approximately 37 months