Clinical Research Directory

Sacituzumab Tirumotecan (Sac-TMT/SKB264) Plus Tagitanlimab (KL-A167) in Patients With Recurrent or Metastatic Esophageal Squamous Cell Carcinoma and Gastric/Gastroesophageal Junction Adenocarcinoma

This is a single-arm, multi-center phase II study to evaluate the efficacy and safety of sacituzumab tirumotecan (Sac-TMT/SKB264) combined with tagitanlimab (KL-A167) as 2nd line therapy for recurrent or metastatic esophageal squamous cell carcinoma (ESCC) or gastric/gastroesophageal junction adenocarcinoma (G/GEJA). A total of 75 participants are planned to be enrolled with 10 in the safety lead-in phase and 33 ESCC and 42 G/GEJA in expansion phase, seperately.

Beamion BCGC-1: A Study to Find a Suitable Dose of Zongertinib Used Alone and in Combination With Other Treatments to Test Whether it Helps People With Different Types of HER2+ Cancer That Has Spread

This study is open to adults aged 18 years and older with different types of HER2+ cancer that has spread and cannot be removed by surgery. People can take part in this study if their tumours show HER2 aberrations and previous treatment was not successful. The purpose of this study is to find a suitable dose of zongertinib that people with different types of HER2+ cancer that has spread can tolerate best when taken together with trastuzumab deruxtecan (T-DXd), with trastuzumab emtansine (T-DM1), with trastuzumab and capecitabine, with zanidatamab, or with mFOLFOX6 (with or without trastuzumab). Another purpose is to check whether zongertinib alone and in combination with other treatments can make tumours shrink. Zongertinib inhibits HER2. HER2 causes cancer cells to grow. In this study, participants receive treatment in cycles. Study participants are treated with zongertinib alone or in combination with other treatments. This study has 2 parts. In Part 1, participants in different groups receive increasing doses of zongertinib. In Part 2, participants are put into different groups by chance. Each group receives a different dose of zongertinib. Every participant has an equal chance of being in each group. During the study, the participants visit the study site regularly. In this study, researchers want to find the highest dose of zongertinib that participants can tolerate when taken together with other treatments. To find this out, researchers look at certain severe health problems that a number of participants have. The doctors regularly check the size of the tumour with imaging methods (CT/MRI) during the study. The doctors also regularly check participants' health and take note of any unwanted effects.

Chemoradiotherapy and SHR-1701 in Patients With Unresectable Gastric Cancer

Gastric Cancer is one of the leading causes of cancer-related death worldwide, and patients with unresectable locally advanced or metastatic disease have a poor prognosis. This study aims to evaluate the safety and efficacy of radiotherapy combined with CAPOX and SHR-1701, a PD-L1/TGF-β bispecific antibody, in patients with unresectable locally advanced or metastatic gastric or gastroesophageal junction adenocarcinoma. By improving local tumor control and enhancing systemic antitumor activity, this study seeks to increase the opportunity for curative-intent resection and improve survival outcomes in patients with advance gastric cancer.

A Study Comparing BL-M05D1 With the Investigator's Choice of Treatment Regimen in Patients With Claudin (CLDN)18.2-Positive Advanced Gastric Cancer or Gastroesophageal Junction Adenocarcinoma (GC/GEJC) Who Have Received Prior First-Line Treatment

This trial is a registrational Phase III, randomized, open-label, multicenter study to evaluate the efficacy and safety of BL-M05D1 in patients with Claudin (CLDN) 18.2-positive advanced gastric cancer or gastroesophageal junction adenocarcinoma (GC/GEJC) who have received prior first-line treatment.

HIPEC Priming Followed by Serplulimab Plus SOX/XELOX in Locally Advanced Gastric Cancer

Patients with locally advanced gastric cancer (LAGC), particularly those with serosal invasion, remain at high risk of peritoneal recurrence despite standard perioperative treatment. Hyperthermic intraperitoneal chemotherapy (HIPEC) may eradicate free intraperitoneal tumor cells and microscopic peritoneal disease while potentially enhancing systemic anti-tumor immune activation. This is a prospective, single-center, single-arm exploratory study evaluating a HIPEC priming strategy followed by serplulimab-based neoadjuvant therapy in patients with locally advanced gastric cancer (cT3-4aN+M0). Eligible patients will undergo diagnostic laparoscopy confirming no visible peritoneal metastasis (P0) and negative peritoneal cytology (CY0), followed by docetaxel-based HIPEC. After recovery from HIPEC, patients will initially receive one cycle of serplulimab combined with fluoropyrimidine monotherapy (S-1 or capecitabine), followed by subsequent cycles of serplulimab combined with SOX/XELOX chemotherapy prior to radical gastrectomy. The primary endpoints are pathological complete response (pCR) rate and major pathological response (MPR) rate. Secondary endpoints include R0 resection rate, objective response rate (ORR), peritoneal recurrence-free survival (PRFS), overall survival (OS), and safety.

Neoadjuvant RCT Versus CT for Patients With Locally Advanced, Potentially Resectable Adenocarcinoma of the GEJ

This is a multicenter, prospective, randomized, stratified, controlled, open-label study comparing neoadjuvant radiochemotherapy with FLOT versus FLOT chemotherapy alone für patients with locally advanced, potentially resectable adenocarcinoma of the gastroesophageal junction (GEJ)

A Study of SGN-CEACAM5C in Adults With Advanced Solid Tumors

This clinical trial is studying advanced solid tumors. Solid tumors are cancers that start in a part of your body like your lungs or liver instead of your blood. Once tumors have grown bigger in one place but haven't spread, they're called locally advanced. If your cancer has spread to other parts of your body, it's called metastatic. When a cancer has gotten so big it can't easily be removed or has spread to other parts of the body, it is called unresectable. These types of cancer are harder to treat. Participants in this study must have cancer that has come back or did not get better with treatment. Participants must have a solid tumor cancer that can't be treated with standard of care drugs. This clinical trial uses an experimental drug called PF-08046050. PF-08046050 is a type of antibody-drug conjugate or ADC. ADCs are designed to stick to cancer cells and kill them. They may also stick to some normal cells. This study will test the safety of PF-08046050 in participants with solid tumors that are hard to treat or have spread throughout the body. This study has 5 different study parts. Part A and Part B of the study will find out how much PF-08046050 should be given to participants. Part C will use the information from Parts A and B to see if PF-08046050 is safe and if it works to treat certain solid tumor cancers. Part D and E of the study, together with information from Parts A and B, will find out how much PF-08046050 should be given in combination with other anti-cancer agents. Part E will use the information from Parts A, B, and D to see if PF-08046050 is safe in combination with other anti-cancer agents and if it works to treat a certain solid tumor.

A Study of Sigvotatug Vedotin in Advanced Solid Tumors

This trial will look at a drug called sigvotatug vedotin (SGN-B6A) alone and with pembrolizumab, with or without chemotherapy, to find out whether it is safe for people who have solid tumors. It will study sigvotatug vedotin to find out what its side effects are. A side effect is anything the drug does besides treating cancer. It will also study whether sigvotatug vedotin works to treat solid tumors. The study will have four parts. * Part A of the study will find out how much sigvotatug vedotin should be given to participants. * Part B will use the dose found in Part A to find out how safe sigvotatug vedotin is and if it works to treat solid tumors. * Part C of the study will find out how safe sigvotatug vedotin is in combination with these other drugs. * Part D will include people who have not received treatment. This part of the study will find out how safe sigvotatug vedotin is in combination with these other drugs and if these combinations work to treat solid tumors. * In Parts C and D, participants will receive sigvotatug vedotin with either: * Pembrolizumab or, * Pembrolizumab and carboplatin, or * Pembrolizumab and cisplatin.

Nivolumab and Ipilimumab in Treating Patients With Esophageal and Gastroesophageal Junction Adenocarcinoma Undergoing Surgery

This phase II/III trial studies the usefulness of treatment with nivolumab and ipilimumab in addition to standard of care chemotherapy and radiation therapy in patients with esophageal and gastroesophageal junction adenocarcinoma who are undergoing surgery. Immunotherapy with antibodies, such as nivolumab and ipilimumab, may remove the brake on the body's immune system and may interfere with the ability of tumor cells to grow and spread. Chemotherapy and radiation therapy may reduce the tumor size and the amount of normal tissue that needs to be removed during surgery. A combined treatment with nivolumab and ipilimumab, chemotherapy, and radiation therapy might be more effective in patients with esophageal and gastroesophageal junction adenocarcinoma who are undergoing surgery.

Collecting Blood Samples From Patients With and Without Cancer to Evaluate Tests for Early Cancer Detection

This study collects blood and tissue samples from patients with cancer and without cancer to evaluate tests for early cancer detection. Collecting and storing samples of blood and tissue from patients with and without cancer to study in the laboratory may help researchers develop tests for the early detection of cancers.

Tadalafil Effect + Chemotherapy in Resectable Gastric/GEJ Cancer

The goal of this clinical trial is to assess the ability of Tadalafil alone and in combination with neoadjuvant FLOT (5-Fluorouracil, Oxaliplatin, and Docetaxel) chemotherapy to suppress myeloid derived suppressor cells (MDSCs) in patients with resectable gastric or gastroesophageal junction adenocarcinoma. Resectable means the tumor may be removed through surgical intervention. Neoadjuvant chemotherapy is chemotherapy received before the primary course of treatment i.e.surgical intervention. The main questions it aims to answer are: * Is Tadalafil treatment with FLOT feasible and safe? * How does tadalafil treatment with FLOT affect the tumor microenvironment (TME)? * Will 8 weeks of neoadjuvant exposure to tadalafil with chemotherapy reduce MDSCs in the TME? Participants will receive Tadalafil for 14 days followed by combination of Tadalafil + FLOT for approximately 8 weeks as a part of standard of care neoadjuvant treatment in the window between cancer diagnosis and surgical intervention to remove their tumor. Tumor tissue, blood, and urine will be collected at the start of the study, after 2 weeks of treatment with Tadalafil alone, and around the time of surgical intervention. Saliva will also be collected at the start of the study.

A Study of Disitamab Vedotin With Other Anticancer Drugs in Solid Tumors

This clinical trial is studying solid tumor cancers. A solid tumor is one that starts in part of your body like your lungs or liver instead of your blood. Once they've grown bigger in one spot or spread to other parts of the body, they're harder to treat. This is called advanced or metastatic cancer. Participants in this study must have breast cancer or gastric cancer. Participants must have tumors that have HER2 on them. This allows the cancer to grow more quickly or spread faster. There are few treatment options for patients with advanced or metastatic solid tumors that express HER2. This clinical trial uses an experimental drug called disitamab vedotin (DV). Disitamab vedotin is a type of antibody drug conjugate or ADC. ADCs are designed to stick to cancer cells and kill them. This clinical trial uses a drug called tucatinib, which has been approved to treat cancer in the United States and some other countries. This drug is sold under the brand name TUKYSA®. This study will test how safe and how well DV with tucatinib works for participants with solid tumors. This study will also test what side effects happen when participants take these drugs. A side effect is anything a drug does to the body besides treating the disease.

Sonesitatug Vedotin in Combination With Capecitabine With or Without Rilvegostomig in Participants With Advanced or Metastatic Gastric, Gastroesophageal Junction, or Esophageal Adenocarcinoma Expressing Claudin18.2

The purpose of this study is to evaluate the efficacy and safety of sonesitatug vedotin in combination with capecitabine with or without rilvegostomig in first-line (1L) Claudin18.2 (CLDN18.2)-positive, human epidermal growth factor receptor 2 (HER2)-negative, gastric, gastroesophageal junction (GEJ), and esophageal adenocarcinoma.

Testing Immunotherapy (Atezolizumab) With or Without Chemotherapy in Locoregional MSI-H/dMMR Gastric and Gastroesophageal Junction (GEJ) Cancer

This phase II trial compares atezolizumab in combination with chemotherapy (docetaxel, oxaliplatin, leucovorin calcium, fluorouracil, capecitabine) to atezolizumab alone for controlling the growth and/or spreading of the disease in patients with gastric or gastroesophageal junction (JEG) cancer that has not spread from where it first started (local) or only has spread to nearby lymph nodes or tissue (locoregional) and has high microsatellite instability (MSI-H) and mismatch repair deficiency (dMMR). The mismatch repair (MMR) system in the body corrects errors made during the copying of DNA and serves as a proofreading function. If this system isn't working correctly, mutations (changes) in DNA occur which can allow the cancer to grow or spread. This is called dMMR (deficient mismatch repair) . MSI-H describes cancer cells that have a high number of mutations within microsatellites. For example, microsatellite testing that shows mutations in 30% or more microsatellites is called microsatellite instability-high (MSI-H). Microsatellites are short, repeated sequences of DNA. There is evidence that MSI-H/ dMMR gastric or GEJ tumors respond well to immunotherapy. Immunotherapy with monoclonal antibodies, such as atezolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Docetaxel is in a class of medications called taxanes. It stops tumor cells from growing and dividing and may kill them. Oxaliplatin is in a class of medications called platinum-containing antineoplastic agents. It damages the cell's DNA and may kill tumor cells. Capecitabine is in a class of medications called antimetabolites. It is taken up by tumor cells and breaks down into fluorouracil, a substance that kills tumor cells. Chemotherapy drugs such as leucovorin calcium and fluorouracil work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Using atezolizumab as immunotherapy with and following chemotherapy versus atezolizumab alone prior to and after surgery may shrink or stabilize the tumor in patients with MSI-H/dMMR localized gastric or GEJ cancer and may increase the length of time after treatment that cancer does not come back or get worse.

Hyperthermic Intraperitoneal Chemotherapy With Cisplatin and Paclitaxel for Gastric Cancer at High Risk of Peritoneal Recurrence

This phase II trial tests how well concentrating heated (hyperthermic) chemotherapy in the area that contains the abdominal organs (intraperitoneal \[IP\]) at the time of surgery works in treating patients with gastric or gastroesophageal junction adenocarcinoma at high risk of the cancer coming back to the abdominal cavity (peritoneal) after a period of improvement (recurrence). Recurrence in the peritoneum often occurs within the first 18 months after surgery. This is thought to be due to tumor cells that may scatter and spread during surgery. Cisplatin is in a class of medications known as platinum-containing compounds. It works by killing, stopping or slowing the growth of tumor cells. Paclitaxel is in a class of medications called antimicrotubule agents. It stops tumor cells from growing and dividing and may kill them. Paclitaxel alone and in combination with other chemotherapy agents have been shown to be effective treatments for gastric tumors. However, systemic delivery of these drugs has not been shown to be effective in treating peritoneal metastasis. Hyperthermic intraperitoneal chemotherapy (HIPEC) is a procedure that involves the infusion of a heated chemotherapy solution, such as cisplatin and paclitaxel, that circulates into the abdominal cavity. Giving HIPEC with cisplatin and paclitaxel at the time of surgery may reduce peritoneal recurrence in patients with gastric or gastroesophageal junction adenocarcinoma at high risk.

Aldesleukin With Nivolumab and Standard Chemotherapy for Treatment of Gastric Cancer With Peritoneal Metastasis

This phase Ib trial test effects of aldesleukin in combination with nivolumab and standard chemotherapy in treating patients with gastric cancer that has spread to the tissue lining of the abdomen (peritoneal metastasis). Aldesleukin is similar to a protein that naturally exists in the body that stimulates the immune system to fight infections. Immunotherapy with monoclonal antibodies, such as nivolumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Chemotherapy drugs, such as leucovorin calcium, fluorouracil, and oxaliplatin, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving aldesleukin in combination with nivolumab and standard chemotherapy may work better in treating patients with gastric cancer with peritoneal metastasis.

A Study of TRK-950 When Used in Combination With Ramucirumab and Paclitaxel in Patients With Gastric Cancer

This study will assess the efficacy, safety, optimal dose and ADA and NAbs development of TRK-950 at two separate dose levels in combination with ramucirumab and paclitaxel (RAM+PTX) as compared with RAM + PTX treatment alone in participants with gastric or gastro-esophageal junction (GEJ) adenocarcinoma.

Objective Sleep Characteristics and Neoadjuvant Immunotherapy Response in Gastric/GEJ Cancer

This prospective observational study will enroll 120 patients with locally advanced gastric or gastroesophageal junction adenocarcinoma who are scheduled to receive neoadjuvant immunotherapy followed by radical surgery. Non-invasive objective sleep monitoring will be performed during the neoadjuvant treatment period to assess sleep characteristics, including sleep duration, sleep efficiency, device-estimated deep sleep proportion, nocturnal awakenings, sleep regularity, heart rate, and heart rate variability. The primary objective is to evaluate the association between objective sleep characteristics and major pathological response (MPR) after neoadjuvant immunotherapy. This study will not alter standard treatment decisions, surgical procedures, or perioperative management.

Emotional Distress and Pathologic Response in Locally Advanced Gastric/GEJ Adenocarcinoma

This is a single-center, prospective observational cohort study designed to evaluate the association between pretreatment emotional distress and pathologic response to perioperative immunotherapy in patients with locally advanced gastric or gastroesophageal junction adenocarcinoma. A total of 120 patients planned for neoadjuvant immunotherapy followed by curative surgery will be enrolled. Emotional distress will be assessed using the PHQ-9 and GAD-7 before treatment initiation and at prespecified time points during treatment. Participants will be classified into an emotional distress group or a non-emotional distress group according to predefined criteria. The primary endpoint is major pathological response (MPR). Secondary endpoints include pathological complete response (pCR), R0 resection rate, event-free survival (EFS), recurrence-free survival (RFS), and overall survival (OS). Exploratory analyses will assess dynamic changes in emotional distress and their associations with peripheral stress markers, peripheral immune markers, and tumor immune microenvironment features.

A Study to Investigate Tislelizumab Administered as Subcutaneous Injection Versus Intravenous Infusion Plus Chemotherapy in Patients With Unresectable or Metastatic Gastric or Gastroesophageal Junction Adenocarcinoma

This study is designed to assess the levels of drug exposure following treatment with tislelizumab administered as a subcutaneous (SC) injection compared to intravenous infusion (IV) as first-line therapy in adults with gastric or gastroesophageal junction (GEJ) that is locally advanced and cannot be surgically removed or has spread from the stomach to other areas of the body. Approximately 351 patients will be participating in this study. The study is composed of a screening period, a treatment period, and a follow-up period.

Mannatide Combined With CAPOX and Tislelizumab for Advanced Gastric Cancer.

This is a multicenter, open-label, single-arm phase II study evaluating the efficacy and safety of mannatide in combination with CAPOX chemotherapy and tislelizumab as first-line treatment for patients with recurrent or metastatic gastric adenocarcinoma or gastroesophageal junction adenocarcinoma. Eligible patients will receive oxaliplatin, capecitabine, tislelizumab, and oral mannatide. Tumor response will be assessed according to RECIST version 1.1. Patients without disease progression after induction treatment may continue maintenance therapy with capecitabine, tislelizumab, and mannatide. The primary objective is to evaluate objective response rate (ORR). Secondary objectives include progression-free survival (PFS), overall survival (OS), disease control rate (DCR), duration of response (DoR), and safety. Exploratory analyses will investigate immune microenvironment changes and potential predictive biomarkers using blood, tumor tissue, and stool samples.

Testing the Addition of Paclitaxel Administered Into the Abdominal Cavity Combined With Chemotherapy for Patients With Gastric Cancer Spread to the Abdominal Cavity

This study is being done to answer the following questions: Can we lower the chance of your gastric cancer from growing or spreading by administering paclitaxel chemotherapy directly into your abdominal cavity in addition to chemotherapy given through a vein in your arm? Will administering paclitaxel chemotherapy directly into your abdominal cavity, in addition to chemotherapy given through a vein in your arm help you live longer? We are doing this study because we want to find out if this approach is better or worse than the usual approach for your gastric cancer. The usual approach is defined as care most people get for gastric cancer. If you decide to take part in this study, you will first receive a surgical procedure called a diagnostic laparoscopy. This will help the study doctors learn more about your gastric cancer. Laparoscopy is a minimally invasive surgery for which you will be placed under general anesthesia. Then the surgeon will make small incisions (5mm) on your belly through which a camera and thin instruments are introduced to evaluate the abdomen. This procedure takes about 1 hour to complete. Your study group will be assigned during the surgery. The study groups are described further in the 'What are the study groups?' section below. If you are placed into the study group 1, you will not have an intraperitoneal port (a small device which is placed under the skin and fat of your upper abdomen and a tube that is placed into the abdomen). If you are placed into the study group 2, you will have an intraperitoneal port placed. The reason is that in addition to standard chemotherapy, which is given through a vein in your arm, this port will be used to deliver the medication paclitaxel directly inside your abdomen when you are ready to start study treatment. It is important to know that you will not know your study group until after the surgery is over. This is because information that is learned during the surgery will help determine which study group you are put in. Once you have fully healed from this surgery, you will start study treatment. Depending on which study group you are assigned, you will either receive a standard chemotherapy regimen (the regimen will be chosen by you and your doctor) if you are in study group 1, or paclitaxel through a tube in your belly plus chemotherapy given through a vein in your arm if you are in study group 2. All participants will get treatment for three (3) months after which you will undergo reevaluation. If the disease is under control or responding to treatment, you may continue the assigned treatment until your disease gets worse, the side effects become too severe, or you may be offered a surgical procedure to remove the cancer if the amount of disease is low and can be completely removed as determined by a surgeon. There is a very small chance that during the laparoscopy surgical procedure, the doctor might find something called "intra-abdominal adhesions". These are areas where the stomach has healed previously and created scar tissue. If this scar tissue prevents the surgeon from being able to place a port in the correct area, you would be ineligible to receive the study treatment. If this happens, you may still receive standard of care therapy after your surgery, but you will not be able to continue on the study. If you have more questions about this, you can ask your surgeon or the study team to help. After you finish your study treatment, your doctor or study team will watch you for side effects. They will continue to follow your condition every three (3) months during the first two (2) years, then every six (6) months until year 5. You may be reevaluated with Chest/Abdomen/Pelvis scans every three-six (3-6) months for up to five (5) years if decided by your doctor.

TAIC FOLFOX for Locally Advanced G/GEJA

Gastric cancer is the fifth most common malignancy worldwide in terms of both incidence and mortality. The majority of cases are diagnosed at advanced stage-often presenting with severe complications such as malignant stricture, obstruction, bleeding, and cancer-related malnutrition-which impinge on quality of life and survival outcomes. For patients with unresectable or metastatic gastric cancer and gastroesophageal junction adenocarcinoma (G/GEJA), first-line systemic therapy remains predominantly platinum- and fluoropyrimidine-based combination chemotherapy, and targeted agents or immunotherapy can be added based on the expression of biomarkers. Under this standard approach, the median overall survival (mOS) for localized unresectable G/GEJA is approximately 14-20 months. For metastatic G/GEJA, the prognosis remains poor with an mOS of less than 1 year, despite the proven efficacy of chemotherapeutic agents. Moreover, up to 25% of cancer survivors report a significant decline in quality of life due to gastrointestinal symptoms during, soon after, or many years after treatment. Interventional oncology approaches-including trans-arterial infusion chemotherapy (TAIC), embolization (TAE), and chemoembolization (TACE)-represent promising locoregional therapeutic strategies. TAIC allows for the direct delivery of cytotoxic agents into the tumor-feeding arteries, thereby maximizing intra-tumoral drug concentration. As one of the most well-recognized applications, hepatic arterial infusion chemotherapy (HAIC) has been demonstrated in liver cancer by elevating local drug exposure, markedly enhancing antitumor efficacy while minimizing systemic adverse effects. Moreover, chemotherapeutic agents may exert secondary systemic activity against clinically or subclinically disseminated metastases upon systemic circulation, contributing to a sustained "secondary chemotherapy" effect. Owing to its favorable safety profile and preserved antitumor activity, TAIC is particularly suited for frail or elderly patients who are ineligible for surgery or conventional systemic chemotherapy. Given the persistent limitations of current therapeutic paradigms, the feasibility and safety of trans-arterial therapy in the treatment of anti-tumor, hemostasis and obstruction relief for locally advanced G/GEJC remains urgent. The present study aimed to assess the efficacy and safety of TAIC for locally advanced G/GEJA.

A Phase Ⅲ Study of Rilvegostomig in Combination With Fluoropyrimidine and Trastuzumab Deruxtecan as the First-line Treatment for HER2-positive Gastric Cancer

This is a Phase Ⅲ, randomized, open-label, Sponsor-blinded, 3-arm, global, multicenter study assessing the efficacy and safety of rilvegostomig in combination with fluoropyrimidine and T-DXd (Arm A) compared to trastuzumab, chemotherapy, and pembrolizumab (Arm B) in HER2-positive locally advanced or metastatic gastric or GEJ adenocarcinoma participants whose tumors express PD L1 CPS ≥ 1. Rilvegostomig in combination with trastuzumab and chemotherapy will be evaluated in a separate arm (Arm C) to assess the contribution of each component in the experimental arm.