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)

NCT07302347 | Recruiting Phase 1

• 3 other identifiers: 3475-G21MK-3475-G21jRCT2041250120
• Study Type: interventional
• Target: 20
• Locations: 1 country
• Sites: 7

Brief 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

Conditions

Malignant Neoplasm; Carcinoma, Merkel Cell; Lymphoma

Outcome Measures

Primary Outcomes (6)

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

  An AE is any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. An AE can therefore be any unfavourable and unintended sign (including an abnormal laboratory finding, for example), symptom, or disease temporally associated with the use of a study intervention. The number of participants with solid tumors or lymphomas who experience an AE will be reported.

  Up to approximately 28 months

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

  An AE is any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. An AE can therefore be any unfavourable and unintended sign (including an abnormal laboratory finding, for example), symptom, or disease temporally associated with the use of a study intervention. The number of participants with solid tumors or lymphomas who discontinue study treatment due to an AE will be reported.

  Up to approximately 25 months

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

  AUC is defined as the area under the concentration-time curve of pembrolizumab. Blood samples will be collected at specified intervals for the determination of AUC. AUC in participants with solid tumors or lymphomas will be reported.

  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

  Cmax is defined as the maximum concentration of pembrolizumab reached. Blood samples will be collected at pre-specified intervals for the determination of Cmax. Cmax in participants with solid tumors or lymphomas will be reported.

  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

  Cmin is defined as the minimum concentration of pembrolizumab observed in plasma after its administration and just prior to administration of a subsequent dose. Blood samples will be collected at pre-specified timepoints to determine Cmin. Cmin in participants with solid tumors or lymphomas will be reported.

  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)

  ORR is defined as complete response (CR: disappearance of all target lesions) or partial response (PR: at least a 30% decrease in the sum of diameters of target lesions) per RECIST 1.1 as assessed by blinded independent central review (BICR). ORR in participants with Merkel cell carcinoma will be reported.

  Up to approximately 37 months

Secondary Outcomes (24)

• Arm 1: ORR per RECIST 1.1 by Investigator Assessment

  Up to approximately 46 months

• Arm 1: ORR per Lugano Classification by Investigator Assessment

  Up to approximately 46 months

• Arm 1: Duration of Response (DOR) per RECIST 1.1 by Investigator Assessment

  Up to approximately 46 months

• Arm 1: DOR per Lugano Classification by Investigator Assessment

  Up to approximately 46 months

• Arm 1: Disease Control (DCR) per RECIST 1.1 by Investigator Assessment

  Up to approximately 46 months

Study Arms (2)

Arm 1: Pembrolizumab in Pediatric Participants with Solid Tumors or Lymphomas

EXPERIMENTAL

Pediatric participants with solid tumors or lymphomas receive 2 mg/kg pembrolizumab via intravenous (IV) infusion every 3 weeks (Q3W) on Day 1 of each 21 day cycle for up to 17 or 35 cycles.

Biological: Pembrolizumab

Arm 2: Pembrolizumab in Adult Participants with Merkel Cell Carcinoma (MCC)

EXPERIMENTAL

Adult participants with MCC receive 400 mg pembrolizumab via IV infusion on Day 1 of each 42 day (6 week) cycle, for up to 18 cycles.

Biological: Pembrolizumab

Interventions

Pembrolizumab BIOLOGICAL

25 mg/mL solution for intravenous infusion.

Also known as: MK-3475

Arm 1: Pembrolizumab in Pediatric Participants with Solid Tumors or Lymphomas; Arm 2: Pembrolizumab in Adult Participants with Merkel Cell Carcinoma (MCC)

Eligibility Criteria

• Age: 6 Months+
• Sex: all
• Healthy Volunteers: No
• Age Groups: Child (0-17), Adult (18-64), Older Adult (65+)

You may qualify if:

• 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 physician
• Has a documented positive local MSI-H or dMMR test result
• Has radiographically measurable disease based on RECIST 1.1

You may not qualify if:

• Has known additional malignancy that is progressing or has required active treatment
• Has known active (central nervous system) CNS metastases and/or carcinomatous meningitis
• Has active autoimmune disease that has required systemic treatment in past 2 years
• Has history of (noninfectious) pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease
• Has active infection requiring systemic therapy
• Has known history of human immunodeficiency virus (HIV) infection
• Has known history of Hepatitis B infection or known active Hepatitis C virus
• Has undergone solid organ transplant at any time, or prior allogeneic hematopoietic stem cell transplantation within the last 5 years
• Has not adequately recovered from major surgery or has ongoing surgical complications

Sponsors & Collaborators

• Merck Sharp & Dohme LLC: lead

Study Sites (7)

Nagoya City University Hospital ( Site 0003)

Nagoya, Aichi-ken, 467-8602, Japan

RECRUITING

Nagoya City University Hospital ( Site 0007)

Nagoya, Aichi-ken, 467-8602, Japan

RECRUITING

Sapporo Hokuyu Hospital ( Site 0005)

Sapporo, Hokkaido, 003-0006, Japan

RECRUITING

Hyogo Prefectural Kobe Children's Hospital ( Site 0006)

Kobe, Hyōgo, 650-0047, Japan

RECRUITING

National Cancer Center Hospital ( Site 0002)

Chūō, Tokyo, 104-0045, Japan

RECRUITING

National Hospital Organization Kyushu Cancer Center ( Site 0001)

Fukuoka, 811-1395, Japan

RECRUITING

University Hospital,Kyoto Prefectural University of Medicine ( Site 0004)

Kyoto, 602-8566, Japan

RECRUITING

Related Links

• Merck Clinical Trials Information

MeSH Terms

Conditions

Neoplasms; Carcinoma, Merkel Cell; Lymphoma

Interventions

pembrolizumab

Condition Hierarchy (Ancestors)

Polyomavirus Infections; DNA Virus Infections; Virus Diseases; Infections; Tumor Virus Infections; Carcinoma, Neuroendocrine; Neuroendocrine Tumors; Neuroectodermal Tumors; Neoplasms, Germ Cell and Embryonal; Neoplasms by Histologic Type; Adenocarcinoma; Carcinoma; Neoplasms, Glandular and Epithelial; Neoplasms, Nerve Tissue; Lymphoproliferative Disorders; Lymphatic Diseases; Hemic and Lymphatic Diseases; Immunoproliferative Disorders; Immune System Diseases

Study Officials

• Medical Director

  Merck Sharp & Dohme LLC

  STUDY DIRECTOR

Central Study Contacts

Toll Free Number

CONTACT

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

Study Design

• Study Type: interventional
• Phase: phase 1
• Allocation: NON RANDOMIZED
• Masking: SINGLE
• Who Masked: OUTCOMES ASSESSOR
• Masking Details: No blinding for Arm 1. Outcomes assessor blinded for Arm 2.
• Purpose: TREATMENT
• Intervention Model: PARALLEL
• Sponsor Type: INDUSTRY
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: December 11, 2025
• First Posted: December 24, 2025
• Study Start (Estimated): June 30, 2026
• Primary Completion (Estimated): March 30, 2029
• Study Completion (Estimated): December 31, 2029
• Last Updated: June 12, 2026

Record last verified: 2026-06

Data Sharing

• IPD Sharing: Will share

Locations

JP (7)