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Study of PF-08634404 with chemotherapy drug combination in previously untreated patients with locally advanced or metastatic gastric and gastroesophageal adenocarcinoma

Fast replyRegistered drugNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study looks at people who have never been treated for locally advanced or metastatic gastric adenocarcinoma, gastroesophageal junction adenocarcinoma, or esophageal adenocarcinoma, which are cancers that start in the stomach, the area where the esophagus meets the stomach, or the lower part of the esophagus and have spread. The purpose of the study is to find out whether adding the experimental drug PF-08634404 to standard chemotherapy can control the cancer and be safe. The experimental group receives the new drug together with a combination of chemotherapy medicines including the pill capecitabine, the IV drugs fluorouracil, oxaliplatin, and calcium folinate. The comparison group receives the approved immunotherapy medicine nivolumab with the same chemotherapy, and a separate group may receive an IV fluid of sodium chloride as a placebo.

Participants will be given the assigned medicines by IV infusion or by mouth in repeated cycles that last a few weeks, and they will have regular doctor visits, blood tests, and imaging scans to see how the tumors are responding. Doctors will use a standard system called RECIST to measure changes in tumor size, and side effects will be recorded using the grading system known as CTCAE. The study will track how long the cancer stays under control, described as progression‑free survival, and how long participants live, described as overall survival, along with any side effects that occur.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Treatment arm assignment

    After enrollment you are placed in either the experimental arm that uses pf-08634404 together with chemotherapy, or the control arm that uses nivolumab together with chemotherapy and a placebo called sodium chloride.

    The assignment is made by the study team and you will receive the appropriate medications according to that assignment.

  2. Step 2

    First intravenous infusion

    On the first study day you receive an intravenous (iv) infusion of the assigned study drug (pf-08634404 or nivolumab) at a dose recorded as 0 mg/m2 in the protocol.

    The iv infusion is administered through a vein by a healthcare professional.

  3. Step 3

    Oral chemotherapy administration

    You take the oral chemotherapy drug capecitabine by mouth at a dose recorded as 0 mg/m2 in the protocol.

    The exact timing and number of daily doses are defined in the study schedule.

  4. Step 4

    Additional intravenous chemotherapy

    During the same treatment cycle you receive additional intravenous chemotherapy agents:

    fluorouracil (dose 0 mg/m2), oxaliplatin (dose 0 mg/m2), and calcium folinate (dose 0 mg/m2).

    Each drug is infused through a vein according to the study protocol.

  5. Step 5

    Repeat treatment cycles

    The combination of iv infusions and oral medication is repeated in multiple cycles for the duration of the study.

    Cycles continue until the study ends, disease progression is observed, or unacceptable side effects occur.

  6. Step 6

    Scheduled assessments

    Throughout the trial you undergo regular assessments such as imaging scans, blood tests, and safety evaluations.

    These assessments are used to measure the effect of the treatment and to monitor any adverse events.

Who can join the trial?

9 criteria

  • You must be 18 years of age or older (or meet the minimum legal age for consent in your country) when you are screened for the study.
  • Your cancer must be confirmed by a lab test that looks at the tissue (histologically) or cells (cytologically) and be a type called adenocarcinoma of the stomach, the area where the stomach meets the esophagus, or the esophagus itself, and it must be either locally advanced unresectable (cannot be removed by surgery) or metastatic (has spread to other parts of the body).
  • You need to have at least one spot that doctors can measure on a scan, using standard rules called RECIST 1.1. If you have had radiation treatment before, the measurable spot must be outside the area that received radiation or must show clear growth.
  • You must not have received any prior systemic therapy (such as chemotherapy or targeted drugs) for your advanced or metastatic cancer.
  • Your overall health must be good enough to have an ECOG PS (performance status) score of 0 or 1, meaning you are fully active or have only slight symptoms.
  • There must be enough tumor tissue saved in a special way (FFPE – formalin‑fixed, paraffin‑embedded) for additional laboratory studies; simple cell samples or bone biopsies are not sufficient.
  • Your tumor must show the protein PD‑L1 at a level of at least 1% using either the TAP (Tumor Area Positivity) or CPS (Combined Positive Score) method, based on tests done locally.
  • Your tumor must be HER2‑negative, meaning it does not have the HER2 protein that some cancers use to grow.
  • You need to have normal or acceptable blood test results showing adequate hematologic (blood), hepatic (liver), and renal (kidney) function.

Who cannot join the trial?

18 criteria

  • Having a type of stomach or esophageal cancer called squamous cell or undifferentiated gastroesophageal cancer (cancer that starts in flat cells or looks very abnormal under a microscope).
  • Having cancer that has spread to the brain or spinal cord (known as active CNS metastases), such as involvement of the brain lining, brainstem, or spinal cord.
  • Having a known deficiency of the enzyme DPD, which can cause dangerous reactions to certain chemotherapy drugs like 5‑fluorouracil or capecitabine.
  • Having a significant risk of hemorrhage (dangerous bleeding) or a fistula (an abnormal connection between organs).
  • Having had major surgery or a serious injury within the past 4 weeks, or planning major surgery during the study; also having had minor local surgery (except placement of a central line) within the past 3 days and not fully recovered.
  • Having a history of receiving an allogeneic organ transplant or an allogeneic stem cell transplant (transplant from another person).
  • Having experienced severe bleeding (Grade 3 or higher) within 28 days before starting the study, or a history of significant bleeding such as unhealed surgical wounds.
  • Having any current, ongoing, or symptomatic infections.
  • Having serious heart disease or other major health problems that required treatment within the past 6 months.
  • Having an active autoimmune disease that needed systemic treatment (medications that affect the whole body) such as disease‑modifying agents, corticosteroids, or immunosuppressive drugs in the past 2 years (certain conditions like vitiligo, psoriasis, type 1 diabetes, resolved childhood asthma, or Sjögren’s syndrome are allowed).
  • Having a history of non‑infectious or drug‑induced lung inflammation (ILD pneumonitis) that was treated with steroids, recurred after immunotherapy, is currently being treated, or is suspected on imaging.
  • Having side effects from previous cancer treatment that have not improved to mild (Grade 0 or 1) levels, except for hair loss; irreversible side effects such as permanent hearing loss may be considered only after special review.
  • Having moderate or severe nerve problems in the hands or feet (Grade >1 peripheral neuropathy) at the start of the study.
  • Having a history of esophageal varices (enlarged veins in the esophagus), severe stomach ulcers, unhealed wounds, a gastrointestinal perforation (a hole), an abnormal passage (fistula), blockage (obstruction), an intra‑abdominal abscess (pus collection), or serious gastrointestinal bleeding within the past 6 months.
  • Having another type of cancer within the past 3 years, or still having disease from a previous cancer, unless it was a very low‑risk cancer (for example, certain skin cancers, early‑stage prostate cancer, carcinoma in situ of the cervix, ductal carcinoma in situ, or Stage I uterine cancer).
  • Being known or suspected to have hypersensitivity (allergy) to any part of the study drug or its inactive ingredients (excipients).
  • Having any other situation that, in the investigator’s opinion, could increase the risks of the study or make the results difficult to interpret.
  • Having any medical or psychiatric condition, including active thoughts of suicide in the past year or suicidal behavior in the past 5 years, or laboratory abnormalities that could raise the risk of participating in the study.
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Investigated drugs

  • Nivolumab

    is an immune‑based medicine that helps the body’s own immune system recognize and attack cancer cells. In this study it is used together with chemotherapy as the standard treatment to compare against the new experimental therapy.

  • PF-08634404

    is a new investigational drug being tested for the first time in people with advanced stomach or esophageal cancer. It is given together with chemotherapy to see if it can improve how long patients live and how long the cancer stays under control.

  • Capecitabine

    is an oral chemotherapy medicine that turns into a cancer‑killing drug inside the body. In the trial it is part of the chemotherapy regimen that is combined with either the experimental drug or the standard immune therapy.

  • Fluorouracil

    is a well‑known chemotherapy drug that stops cancer cells from growing. It is given through an IV and is included in the chemotherapy combination used in both study arms.

  • Oxaliplatin

    is another chemotherapy agent that damages the DNA of cancer cells, helping to stop them from multiplying. It is administered by IV and is part of the chemotherapy mix given to all participants.

  • Calcium folinate

    is a supportive medication that is often given with certain chemotherapy drugs to reduce side effects and improve how the chemotherapy works. In this trial it is used together with the chemotherapy regimen.

What is already known about the treatment

  • Nivolumab

    Nivolumab is given by an intravenous (IV) infusion and is an approved medicine that works by blocking a protein called PD‑1, which helps the immune system recognize and attack cancer cells. It is used in many cancers, including advanced gastric and esophageal adenocarcinoma, as part of standard treatment. By releasing the brake on immune cells, it boosts the body’s natural ability to fight tumors. It belongs to the class of immune checkpoint inhibitors, a type of immunotherapy.

  • PF‑08634404

    PF‑08634404 is administered as an IV infusion of a concentrate that is mixed for delivery, and it is currently an investigational drug being studied in clinical trials. It is being tested for patients with advanced gastric, gastro‑esophageal junction, or esophageal adenocarcinoma together with standard chemotherapy. The compound works by blocking specific signaling pathways that cancer cells need to grow and survive. It is classified as a targeted therapy under development.

  • Sodium Chloride

    Sodium chloride is supplied as an IV solution and is used in this study as a placebo to match the appearance of the active drug. It is a well‑known, approved electrolyte solution that helps maintain fluid and salt balance in the body. It does not treat cancer but simply provides sodium and chloride ions to keep blood volume stable. It is classified as an electrolyte and fluid replacement.

  • Capecitabine

    Capecitabine is taken by mouth as tablets and is an approved chemotherapy drug for several solid tumors, including gastric and esophageal cancers. After swallowing, it is converted inside the body to the active drug 5‑fluorouracil, which interferes with DNA building blocks and stops cancer cells from multiplying. It is used to shrink tumors or slow their growth. Capecitabine belongs to the antimetabolite class of chemotherapy agents.

  • Fluorouracil

    Fluorouracil is given by IV infusion and is a long‑standing chemotherapy medicine for many cancers such as gastric and esophageal adenocarcinoma. It mimics a natural building block of DNA, causing the cancer cells to stop making new DNA and eventually die. It is used alone or with other drugs to treat tumors. Fluorouracil is classified as an antimetabolite chemotherapy agent.

  • Oxaliplatin

    Oxaliplatin is administered by IV infusion and is an approved chemotherapy drug for gastrointestinal cancers, including advanced gastric and esophageal adenocarcinoma. It works by forming strong links (cross‑links) in the DNA of cancer cells, preventing them from copying their genetic material. This stops tumor growth and can shrink existing tumors. Oxaliplatin is a platinum‑based chemotherapy agent.

Investigated diseases

Gastric, gastroesophageal junction, or esophageal adenocarcinoma - This disease is a type of cancer that begins in the glandular cells lining the stomach, the area where the stomach meets the esophagus, or the lower part of the esophagus. It usually starts as a small growth that can grow into the surrounding tissue of the stomach or esophagus. As it enlarges, it may spread to nearby lymph nodes and organs such as the liver or lungs. The cancer can continue to grow and form new tumors in distant parts of the body. Its development can be slow at first and then become faster as it advances.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IVTrial ID2025-524717-86-00Protocol codeC6461016Estimated enrolment840 patientsSponsorPfizer Inc.

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On this site, “treatment” means an investigational medicine being studied in a clinical trial. Its safety and efficacy for the use being studied have not yet been confirmed, some participants may receive a placebo or a comparator medicine, and taking part does not guarantee any health benefit. The decision to take part is made by the doctor at the research site. This site is for information only and does not replace medical advice.

This service is not affiliated with the European Commission, the EMA, or the official CTIS system. Most information comes from publicly available international clinical-trial registries, supplemented by data from academic sites, national regulators and commercial sponsors. On this site, “treatment” and “therapy” mean a medicine being tested in a clinical trial. Its safety and effectiveness in the use being studied are not yet confirmed, some participants may receive a placebo or a comparator, and taking part does not guarantee a health benefit. The doctor at the research site decides who can take part. This site provides information, not medical advice. Certain content and visual elements on this website have been generated or enhanced using artificial intelligence (AI).