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Study of Pembrolizumab with Chemotherapy for Patients with Advanced Gastric 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 gastric adenocarcinoma, which affects the stomach, and gastroesophageal junction adenocarcinoma, which occurs where the stomach meets the esophagus. The study is investigating the effectiveness of a treatment that combines a medication called pembrolizumab (also known by its code name MK-3475) with chemotherapy, compared to a combination of a placebo and chemotherapy. Pembrolizumab is a type of medication that helps the immune system fight cancer cells. The chemotherapy drugs used in this study include cisplatin, capecitabine, fluorouracil, and oxaliplatin.

The purpose of the study is to compare the overall survival of participants receiving pembrolizumab with chemotherapy to those receiving a placebo with chemotherapy. Participants in the study have HER2-negative cancer, which means their cancer cells do not have a protein called HER2 on their surface. The study is designed to be double-blind, meaning neither the participants nor the researchers know who is receiving the pembrolizumab or the placebo. This helps ensure the results are unbiased.

Participants will receive treatment through intravenous infusion, which means the medication is given directly into a vein, and some medications may be taken orally. The study will follow participants over a period to monitor their response to the treatment and any side effects they may experience. The goal is to determine if pembrolizumab, when combined with chemotherapy, can improve survival rates for people with advanced gastric or gastroesophageal junction adenocarcinoma.

The research process

The trial runs in 4 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Joining the study

    Upon joining the study, the participant will be randomly assigned to receive either pembrolizumab or a placebo, both in combination with chemotherapy.

    The study is designed to compare the effects of pembrolizumab with a placebo when used alongside chemotherapy in treating advanced gastric or gastroesophageal junction adenocarcinoma.

  2. Step 2

    Treatment administration

    Participants will receive pembrolizumab or a placebo through an intravenous infusion. The specific dosage and frequency will be determined by the study protocol.

    Chemotherapy will include medications such as cisplatin, capecitabine, fluorouracil, and oxaliplatin. These will be administered either intravenously or orally, depending on the specific drug.

  3. Step 3

    Monitoring and assessments

    Throughout the study, participants will undergo regular monitoring to assess their response to the treatment. This includes measuring the size of the tumor and checking for any side effects.

    Participants will also provide tissue samples for biomarker analysis, which helps in understanding the effectiveness of the treatment.

  4. Step 4

    Completion of treatment

    The treatment period will continue as per the study protocol until the study's estimated end date in October 2025, or until the participant completes the treatment regimen.

    After completing the treatment, participants will have follow-up visits to monitor their health and any long-term effects of the treatment.

Who can join the trial?

10 criteria

  • The patient must have a confirmed diagnosis of advanced or spreading **gastric** (stomach) or **gastroesophageal junction (GEJ)** cancer, with known **PD-L1** status. **PD-L1** is a protein that can affect the immune system's ability to fight cancer.
  • The patient must have **adequate organ function**, which means their organs are working well enough, as shown by lab tests done within 10 days before starting the study treatment.
  • The cancer must be **HER2 negative**. **HER2** is a protein that can affect the growth of cancer cells.
  • Male patients must agree to use **contraception** during the treatment and for 95 days after the last dose of chemotherapy. They should not donate sperm and should avoid heterosexual intercourse unless they are confirmed to be **azoospermic** (unable to produce sperm).
  • Female patients must not be pregnant or breastfeeding. If they can have children, they must agree to use contraception or avoid heterosexual intercourse during the treatment and for a certain period after the last dose of chemotherapy or pembrolizumab. They should not donate eggs or store them for future use during this time.
  • The patient must have a **measurable disease** according to specific criteria used by doctors to assess cancer.
  • The patient must provide a sample of their tumor tissue, either from a previous biopsy or a new one, for analysis. This sample should not be from an area that has been treated with radiation before.
  • The patient must provide a tumor tissue sample that is suitable for **PD-L1 biomarker analysis**. A **biomarker** is a biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease.
  • The patient must provide a tumor tissue sample for **microsatellite instability (MSI) biomarker analysis**. **MSI** is a condition of genetic hypermutability that can affect cancer development.
  • The patient must have an **ECOG performance status** of 0 or 1, which means they are fully active or have some symptoms but can carry out light work. This status is assessed within 3 days before starting the study treatment.

Who cannot join the trial?

10 criteria

  • Patients with other types of cancer besides **gastric** (stomach) and **gastric esophageal junction (GEJ) adenocarcinoma** cannot participate.
  • Patients who are not within the specified age range for the study cannot participate.
  • Patients who are part of a vulnerable population, which means they might need special protection or care, cannot participate.
  • Patients who have medical conditions or are taking medications that could interfere with the study cannot participate.
  • Patients who have previously received certain treatments that might affect the study results cannot participate.
  • Patients who are unable to follow the study procedures or attend required visits cannot participate.
  • Patients who are pregnant or breastfeeding cannot participate.
  • Patients with certain infections or diseases that could affect their immune system cannot participate.
  • Patients who have had a recent major surgery or are planning to have one during the study cannot participate.
  • Patients with a history of severe allergic reactions to the study drugs cannot participate.
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Investigated drugs

Pembrolizumab (MK-3475) is a medication used in this clinical trial to help the body's immune system fight cancer. It is being tested as a first-line treatment for patients with certain types of stomach cancer that cannot be removed by surgery or have spread to other parts of the body. Pembrolizumab is combined with chemotherapy to see if it can improve the overall survival of the participants compared to chemotherapy alone.

What is already known about the treatment

Pembrolizumab – Pembrolizumab is administered intravenously and is currently being studied in clinical trials as a treatment for gastric and gastroesophageal junction adenocarcinoma. It is an approved medication in the field of oncology and is well-documented in medical literature. The main therapeutic indication for pembrolizumab in this trial is as a first-line treatment for HER2 negative, previously untreated, unresectable, or metastatic gastric or gastroesophageal junction adenocarcinoma. At the molecular level, pembrolizumab works by blocking the PD-1 pathway, which helps the immune system recognize and attack cancer cells. It is classified as an immune checkpoint inhibitor.

Investigated diseases

Gastric and Gastric Esophageal Junction Adenocarcinoma – This is a type of cancer that begins in the glandular cells lining the stomach and the area where the stomach meets the esophagus. It typically develops slowly over many years and may start as a pre-cancerous change in the stomach lining. As the disease progresses, it can invade deeper layers of the stomach wall and spread to nearby organs or lymph nodes. Symptoms may include difficulty swallowing, weight loss, stomach pain, and nausea. The disease is more common in older adults and may be associated with certain risk factors like smoking and diet. Early stages might not cause noticeable symptoms, making it challenging to detect until it has advanced.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2023-508890-10-00Protocol codeMK3475-859Estimated enrolment1 565 patientsSponsorMerck Sharp & Dohme LLC

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