A Phase 2/3 interventional study of PF-08634404 and Chemotherapy in Untreated Advanced or Metastatic Gastric, Gastroesophageal Junction , or Esophageal Adenocarcinoma, Metastatic Gastric Cancer and Gastroesophageal Junction Cancer, sponsored by Pfizer. Recruiting at 100 sites in 10 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-09-28.
Sponsored by Pfizer · Phase 2/3, Interventional, and Treatment
This study is being done to learn more about a new medicine called PF-08634404 and how well it works when given with chemotherapy to people with gastroesophageal cancer that is locally advanced (spread to nearby tissues) or has spread to other parts of the body.
To join the study, participants must meet the following conditions:
Be 18 years or older. Have locally advanced or metastatic gastric, gastroesophageal junction or esophageal adenocarcinoma Be treatment naïve for advanced or metastatic disease Be in good physical condition and have healthy organs based on medical tests.
The study has two parts:
The treatment will be given in repeated time periods called cycles.
Exclusion Criteria:
PF-08634404 + Chemotherapy
Biological: PF-08634404 · Drug: Chemotherapy
PF-08634404 + Chemotherapy
Biological: PF-08634404 · Drug: Chemotherapy
Nivolumab + Chemotherapy
Drug: Chemotherapy · Biological: Nivolumab
Participants will receive PF-08634404 intravenously.
Also known as: SSGJ-707
Participants will receive PF-08634404 intravenously in combination with Chemotherapy.
Participants will receive Nivolumab intravenously.
Phase 2: Confirmed Objective response rate (ORR) using RECIST 1.1 as assessed by investigator
Confirmed ORR by investigator is defined as the proportion of participants with confirmed Complete Response (CR) or Partial Response (PR) per RECIST v1.1 as assessed by investigator.
Time frame: Approximately 4 years
Phase 2: Number of participants with treatment-emergent adverse events
Adverse Events (AEs) as characterized by type, frequency, severity (as graded by NCI CTCAE version 5.0), timing, seriousness, and relationship to study intervention.
Time frame: Through 90 days after the last study intervention; Approximately 4 years
Phase 3: Progression Free Survival (PFS) using RECIST 1.1 as assessed by BICR
PFS by BICR is defined as the time from the date of randomization to the date of first documented disease progression per RECIST 1.1 as assessed by BICR, or death due to any cause, whichever occurs first.
Time frame: Approximately 4 years
Phase 3: Overall Survival (OS)
OS is defined as the time from the date of randomization to the date of death due to any cause.
Time frame: Approximately 4 years
Phase 2: Duration of Response (DOR) using RECIST 1.1 as assessed by investigator
DOR by investigator is defined as the time from the first documentation of objective response (CR or PR that is subsequently confirmed) to the date of first documented disease progression per RECIST 1.1 as assessed by investigator, respectively, or death due to any cause, whichever occurs first.
Time frame: Approximately 4 years
Phase 2: Progression Free Survival (PFS) using RECIST 1.1 as assessed by investigator
PFS by investigator is defined as the time from the date of first dose to the date of first documented disease progression per RECIST 1.1 as assessed by investigator, or death due to any cause, whichever occurs first.
Time frame: Approximately 4 years
Phase 2: Overall Survival (OS)
OS is defined as the time from the date of first dose to the date of death due to any cause.
Time frame: Approximately 4 years
Phase 2: Number of participants with laboratory abnormalities
Laboratory abnormalities as characterized by type, frequency, severity (as graded by NCI CTCAE version 5.0), and timing. For laboratory tests without CTCAE grade definitions, results will be categorized as normal, high, low, or not done and be listed.
Time frame: Through 90 days after the last study intervention; Approximately 4 years
Phase 2: Serum concentrations of PF-08634404
Predose and postdose concentrations of PF-08634404
Time frame: Approximately 21 months
Phase 2: Incidence of Anti-Drug Antibody (ADA) against PF-08634404
Time frame: Approximately 21 months
Phase 3: ORR using RECIST 1.1 as assessed by BICR
ORR by BICR is defined as the proportion of participants with a Best Overall Response (BOR) of confirmed CR or confirmed PR per RECIST 1.1 as assessed by BICR.
Time frame: Approximately 4 years
Phase 3: ORR using RECIST 1.1 as assessed by investigator
ORR by investigator is defined as the proportion of participants with a BOR of confirmed CR or confirmed PR per RECIST 1.1 as assessed by investigator.
Time frame: Approximately 4 years
Phase 3: Progression free survival (PFS) using RECIST 1.1 as assessed by investigator
PFS by investigator is defined as the time from the date of randomization to the date of first documented disease progression per RECIST 1.1 as assessed by investigator, or death due to any cause, whichever occurs first
Time frame: Approximately 4 years
Phase 3: DOR using RECIST 1.1 as assessed by BICR
DOR is defined as the time from the first documentation of objective response (CR or PR that is subsequently confirmed) to the date of first documented disease progression per RECIST 1.1 as assessed by BICR, respectively, or death due to any cause, whichever occurs first.
Time frame: Approximately 4 years
Phase 3: DOR using RECIST 1.1 as assessed by investigator
DOR is defined as the time from the first documentation of objective response (CR or PR that is subsequently confirmed) to the date of first documented disease progression per RECIST 1.1 as assessed by investigator, respectively, or death due to any cause, whichever occurs first.
Time frame: Approximately 4 years
Phase 3: PFS2 (PFS after next-line therapy) by investigator
PFS2 is defined as the time from the date of randomization to the date of second objective disease progression or death due to any cause, whichever occurs first
Time frame: Approximately 4 years
Phase 3: Number of participants with treatment-emergent adverse events
AEs as characterized by type, frequency, intensity as graded by NCI CTCAE version 5.0, timing, seriousness, and relationship to study intervention(s)
Time frame: Through 90 days after the last study intervention; Approximately 4 years
Phase 3: Number of participants with laboratory abnormalities
Laboratory abnormalities as characterized by type, frequency, severity (as graded by NCI CTCAE version 5.0), and timing. For laboratory tests without CTCAE grade definitions, results will be categorized as normal, high, low, or not done and be listed.
Time frame: Through 90 days after the last study intervention; Approximately 4 years
Phase 3: Serum concentrations of PF-08634404
Predose and postdose concentrations of PF-08634404
Time frame: Approximately 21 months
Phase 3: Incidence of ADA against PF-08634404
Time frame: Approximately 21 months
Phase 3: Change from baseline in Functional Assessment of Cancer Therapy - Gastric (FACT-Ga) Total score
Time frame: Approximately 4 years
Phase 3: Time to definitive deterioration in FACT-Ga Total score
Time frame: Approximately 4 years
Phase 3: Time to definitive deterioration in Gastric Cancer Subscale (GaCS) score
Time frame: Approximately 4 years
Plan to share: Yes — Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.
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