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Study of Pembrolizumab, Trastuzumab, and Chemotherapy for Patients with HER2 Positive Advanced Stomach or Gastroesophageal Junction Cancer

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What is this trial about?

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

This clinical trial is focused on studying a type of cancer called HER2-positive advanced gastric or gastroesophageal junction adenocarcinoma. This is a form of cancer that affects the stomach or the area where the stomach meets the esophagus. The study is investigating the effectiveness of a treatment combination that includes the drug pembrolizumab, also known by its code name MK-3475, along with trastuzumab and chemotherapy. Chemotherapy involves using drugs to kill cancer cells or stop them from growing. The study also includes a comparison with a placebo, which is a substance with no active medication.

The purpose of the study is to compare how well patients do with the different treatment combinations. Participants will receive either the combination of pembrolizumab, trastuzumab, and chemotherapy or trastuzumab, chemotherapy, and a placebo. The study will monitor how long patients live without the cancer getting worse and their overall survival. The treatment will be given through an intravenous infusion, which means the medication is delivered directly into the bloodstream through a vein. Some of the chemotherapy drugs used in this study include oxaliplatin, capecitabine, cisplatin, and fluorouracil.

Participants in the study will be closely monitored for any side effects or adverse events, which are any unwanted effects of the treatment. The study aims to provide valuable information on the effectiveness and safety of the treatment combinations for patients with HER2-positive advanced gastric or gastroesophageal junction adenocarcinoma. The study is expected to last for a period of time, during which participants will receive regular assessments to track their progress and response to the treatment.

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

    Joining the trial

    Upon joining the trial, you will be informed about the study's purpose and procedures. You will be asked to provide consent to participate.

    You will undergo initial assessments to confirm eligibility, including tests to verify the diagnosis of HER2 positive gastric or gastroesophageal junction adenocarcinoma.

  2. Step 2

    Treatment initiation

    You will begin treatment with a combination of medications. The treatment includes trastuzumab and chemotherapy drugs such as oxaliplatin, capecitabine, cisplatin, and fluorouracil.

    You will receive trastuzumab and oxaliplatin through an intravenous infusion, which means the medication is delivered directly into your bloodstream through a vein.

    The chemotherapy drug capecitabine is taken orally, meaning you will swallow it in pill form.

  3. Step 3

    Randomized treatment

    You will be randomly assigned to receive either pembrolizumab or a placebo. Pembrolizumab is administered through an intravenous infusion.

    A placebo is a substance with no active medication, used to compare the effects of the actual drug.

  4. Step 4

    Ongoing treatment

    You will continue to receive the assigned treatment regimen at regular intervals as determined by the study protocol.

    The duration and frequency of each medication will be explained to you by the study team.

  5. Step 5

    Monitoring and assessments

    Throughout the trial, you will undergo regular assessments to monitor your health and the effectiveness of the treatment.

    These assessments may include physical exams, blood tests, and imaging studies to evaluate the progression of the disease.

  6. Step 6

    Completion of the trial

    At the end of the trial, you will have a final assessment to determine the overall impact of the treatment.

    You will be informed about the results of the study and any potential next steps regarding your treatment.

Who can join the trial?

7 criteria

  • Must have a confirmed diagnosis of **gastric or gastroesophageal junction (GEJ) adenocarcinoma** that is **HER2-positive**. This means the cancer has a specific protein called HER2 on its surface.
  • The cancer must be **locally advanced**, meaning it has spread to nearby areas, or **metastatic**, meaning it has spread to other parts of the body.
  • Must have **measurable disease** as determined by specific medical criteria used by the study doctor.
  • Female participants must not be pregnant or breastfeeding. If they can have children, they must agree to use approved birth control methods.
  • Must have a **performance status** of 0 or 1 on the **ECOG Performance Scale**, which means being fully active or having some symptoms but still able to carry out light work.
  • Must have a **life expectancy** of more than 6 months.
  • Must have **adequate organ function**, meaning the organs are working well enough to participate in the study.

Who cannot join the trial?

10 criteria

  • Patients with any other type of cancer besides gastric or gastroesophageal junction (GEJ) adenocarcinoma cannot participate.
  • Patients who have had another cancer within the last 5 years, except for skin cancer that is not melanoma or in situ cervical cancer, are excluded.
  • Patients with serious heart problems, such as heart failure or a recent heart attack, are not eligible.
  • Patients with uncontrolled high blood pressure cannot join the study.
  • Patients with active infections, including HIV, hepatitis B, or hepatitis C, are excluded.
  • Patients who are pregnant or breastfeeding cannot participate.
  • Patients with known allergies to the study drugs or similar drugs are not eligible.
  • Patients who have received another investigational drug within the last 4 weeks are excluded.
  • Patients with a history of drug or alcohol abuse within the last 6 months cannot join the study.
  • Patients with any condition that the study doctors believe would make it unsafe for them to participate are not eligible.
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Investigated drugs

  • Trastuzumab

    is a medication used in this trial to treat a type of cancer known as HER2 positive advanced gastric or gastroesophageal junction adenocarcinoma. It works by targeting and blocking the function of a protein called HER2, which can promote the growth of cancer cells. By blocking this protein, trastuzumab helps to slow down or stop the growth of the cancer.

  • Pembrolizumab

    is another medication used in this trial. It is an immunotherapy drug that helps the body's immune system fight cancer. Pembrolizumab works by blocking a specific protein on the surface of immune cells, which allows these cells to better recognize and attack cancer cells. This can help to slow down the progression of the cancer and improve survival rates.

What is already known about the treatment

  • Trastuzumab

    Trastuzumab is administered through an intravenous infusion, meaning it is given directly into a vein. It is currently well-established in medical practice and literature as a treatment for certain types of cancer. The main therapeutic indication for Trastuzumab is HER2-positive advanced gastric or gastroesophageal junction adenocarcinoma. At the molecular level, it works by targeting and binding to the HER2 protein on cancer cells, which helps to stop the growth of these cells. Trastuzumab is classified as a monoclonal antibody, a type of targeted cancer therapy.

  • Pembrolizumab

    Pembrolizumab is administered via an intravenous infusion, which involves delivering the medication directly into the bloodstream. It is widely recognized in the medical community and literature as an effective treatment for various cancers. The primary therapeutic use of Pembrolizumab in this context is for HER2-positive advanced gastric or gastroesophageal junction adenocarcinoma. Its mechanism of action involves blocking a protein called PD-1 on immune cells, which enhances the body's immune response against cancer cells. Pembrolizumab is classified as an immune checkpoint inhibitor, a type of immunotherapy.

Investigated diseases

Gastric or gastroesophageal junction adenocarcinoma – This is a type of cancer that forms in the glandular cells lining the stomach or the area where the stomach meets the esophagus. It begins when these cells start to grow uncontrollably, forming a tumor. As the disease progresses, the tumor can invade deeper layers of the stomach wall and spread to nearby lymph nodes and other organs. Symptoms may include difficulty swallowing, weight loss, and stomach pain. The disease can also cause bleeding in the stomach, leading to anemia. Over time, it may metastasize to distant parts of the body, affecting overall health and function.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2023-508253-98-00Protocol codeMK-3475-811Estimated enrolment745 patientsSponsorMerck Sharp & Dohme LLC

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