A Phase 3, randomized, double-blind clinical study of pembrolizumab (MK-3475) plus chemotherapy versus placebo plus chemotherapy as first-line treatment in participants with HER2 negative, previously untreated, unresectable or metastatic gastric or gastroesophageal junction adenocarcinoma (KEYNOTE-859)

Status

Completed

Phases

Phase 3

Study type

Interventional

Source

EU CTIS

Registry ID

CTIS2023-508890-10-00

Acronym

MK3475-859

Enrollment

268

Registered

2024-04-30

Start date

2018-12-05

Completion date

2025-03-03

Last updated

2025-03-19

For informational purposes only — not medical advice. Sourced from public registries and may not reflect the latest updates. Terms

Conditions

Gastric and gastric esophageal junction (GEJ) adenocarcinoma

Brief summary

OS in All Participants, OS In Participants With PD-L1 CPS ≥1, OS In Participants With PD-L1 CPS ≥10

Detailed description

PFS Per RECIST 1.1 Assessed by BICR in All Participants, PFS Per RECIST 1.1 Assessed by BICR In Participants With PD-L1 CPS ≥1, PFS Per RECIST 1.1 Assessed by BICR In Participants With PD-L1 CPS ≥10, ORR Per RECIST 1.1 Assessed by BICR in All Participants, ORR Per RECIST 1.1 Assessed by BICR in Participants With PD-L1 CPS ≥1, ORR Per RECIST 1.1 Assessed by BICR in Participants With PD-L1 CPS ≥10, DOR Per RECIST 1.1 Assessed by BICR in All Participants, DOR Per RECIST 1.1 Assessed by BICR In Participants With PD-L1 CPS ≥1, DOR Per RECIST 1.1 Assessed by BICR In Participants With PD-L1 CPS ≥10, Number of Participants Who Experienced an Adverse Event (AE), Number of Participants Who Discontinued Study Treatment Due To an AE

Interventions

DRUGPlacebo for pembrolizumab

DRUGKEYTRUDA 25 mg/mL concentrate for solution for infusion

DRUGCAPECITABINE

DRUGFLUOROURACIL

DRUGOXALIPLATIN

DRUGCISPLATIN

Eligibility

Sex/Gender

All

Age

18 Years to No maximum

Design outcomes

Primary

Measure	Time frame
OS in All Participants, OS In Participants With PD-L1 CPS ≥1, OS In Participants With PD-L1 CPS ≥10	—

Secondary

Measure	Time frame
PFS Per RECIST 1.1 Assessed by BICR in All Participants, PFS Per RECIST 1.1 Assessed by BICR In Participants With PD-L1 CPS ≥1, PFS Per RECIST 1.1 Assessed by BICR In Participants With PD-L1 CPS ≥10, ORR Per RECIST 1.1 Assessed by BICR in All Participants, ORR Per RECIST 1.1 Assessed by BICR in Participants With PD-L1 CPS ≥1, ORR Per RECIST 1.1 Assessed by BICR in Participants With PD-L1 CPS ≥10, DOR Per RECIST 1.1 Assessed by BICR in All Participants, DOR Per RECIST 1.1 Assessed by BICR In Participants With PD-L1 CPS ≥1, DOR Per RECIST 1.1 Assessed by BICR In Participants With PD-L1 CPS ≥10, Number of Participants Who Experienced an Adverse Event (AE), Number of Participants Who Discontinued Study Treatment Due To an AE	—

Measure

Time frame

—

Countries

Czechia, Denmark, France, Germany, Ireland, Italy, Poland, Spain

Outcome results

None listed

Source: EU CTIS · Data processed: Feb 4, 2026