A Study of ASP2138 Together With Chemotherapy and Pembrolizumab in Adults With Gastric Cancer

Summary

Claudin 18.2 or CLDN18.2 is a protein found on cells in the digestive system. It is also found in some tumors. Researchers are looking at ways to attack CLDN18.2 to help control tumors. ASP2138 is thought to bind to CLDN18.2 and a type of immune cell called a T cell. This "tells" the immune system to attack the tumor. ASP2138 is a potential treatment for people with gastric cancer (also known as stomach cancer) or gastroesophageal junction cancer (GEJ cancer). GEJ is where the tube that carries food (esophagus) joins the stomach.

This study is for people with gastric or GEJ cancer that has spread nearby (locally advanced) and is not removable by surgery (unresectable), or has spread to other parts of the body (metastatic). It is for those whose cancer is human epidermal growth factor receptor 2 (HER2)-negative and CLDN18.2-positive. HER2-negative means the cancer does not have extra HER2 protein, so medicines that target HER2 do not work and are therefore not used. CLDN18.2-positive means people have a certain amount of CLDN18.2 proteins on their cancer cells. In this study, researchers want to learn if ASP2138 given together with standard treatments (chemotherapy and pembrolizumab) help people with HER2-negative and CLDN18.2-positive gastric or GEJ cancer. The main aim is to learn how long people who are given ASP2138 with chemotherapy and pembrolizumab live without their cancer getting worse, compared with placebo given with chemotherapy with or without pembrolizumab, and if they live for longer. Placebo looks like the study treatment but does not have any medicine in it.

The main aim of this study is to check how well ASP2138 works when given together with chemotherapy and pembrolizumab compared with placebo plus chemotherapy with or without pembrolizumab.

People aged 18 years or older with locally advanced unresectable or metastatic gastric or GEJ cancer can take part. Their tumor should be HER2-negative and CLDN18.2-positive. The study doctors will check people for any health conditions that can exclude them from taking part, interfere with the study procedures, or pose an unacceptable risk.

This is a double-blind study. That means the people and the study doctors will not know who will receive which treatment. People will be assigned to one of 2 treatment groups by chance:

Group A: People will receive ASP2138 along with chemotherapy and pembrolizumab. Group B: People will receive placebo along with chemotherapy, with or without pembrolizumab.

People will keep receiving treatment until their cancer gets worse, they have medical problems that require stopping treatment, or a study rule says they must stop. There will be regular safety checks. People will continue to have scans of their tumor until their cancer becomes worse.

Conditions

• Gastric Adenocarcinoma
• Gastroesophageal Junction (GEJ) Adenocarcinoma

Interventions

DRUG

ASP2138

SC Injection

DRUG

Pembrolizumab

IV Infusion

DRUG

Oxaliplatin

IV Infusion

DRUG

Capecitabine

Oral administration

DRUG

Folinic acid

IV Infusion

DRUG

5-FU

IV Infusion or IV bolus

DRUG

Placebo for ASP2138

SC Injection

DRUG

Placebo for Pembrolizumab

IV Infusion

Sponsors & Collaborators

• Astellas Pharma Global Development, Inc.

  lead INDUSTRY

Principal Investigators

• Development Physician · Astellas Pharma Global Development, Inc.

Study Design

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

QUADRUPLE

Model

PARALLEL

Eligibility

Min Age

18 Years

Sex

ALL

Healthy Volunteers

No

Timeline & Regulatory

Start

2026-06-30

Primary Completion

2031-02-28

Completion

2031-02-28

FDA Drug

Yes

Countries

• Puerto Rico

Study Locations