RecruitingPhase 1Phase 2NCT07302347

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)

A Phase I/II Study of Pembrolizumab (MK-3475) in Japanese Pediatric Participants With Specific Solid Tumors or Lymphomas, or in Japanese Adult Participants With Advanced Merkel Cell Carcinoma (KEYNOTE-G21)

Sponsor

Merck Sharp & Dohme LLC

Enrollment

20 participants

Start Date

Mar 31, 2026

Study Type

INTERVENTIONAL

Conditions

Lymphoma Malignant Neoplasm Carcinoma, Merkel Cell

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

Eligibility

Min Age: 6 Months

Inclusion Criteria26

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
For participants with tumor mutational burden-high (TMB-H) 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 radiographically measurable disease based on RECIST 1.1
For participants with MCC:
Has histologically confirmed diagnosis of locoregional MCC that has recurred following standard locoregional therapy with surgery and/or radiation therapy and is not amenable to local therapy or metastatic MCC (Stage IV)
Has radiographically measurable disease based on RECIST 1.1
Arm 2:
For participants with MCC:
Has been untreated for advanced or metastatic disease
Arm 1 \& Arm 2:
Life expectancy of \>3 months (Arm 1) or \>6 months (Arm 2)

Exclusion Criteria9

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