Combination of Osemitamab (TST001), Pembrolizumab and Chemotherapy as First-line Therapy in Advanced or Metastatic GC/GEJ Adenocarcinoma

December 12, 2025 updated by: Suzhou Transcenta Therapeutics Co., Ltd.

A Phase 3, Randomized, Double-blind, Placebo-controlled Study Evaluating Combination of TST001, Pembrolizumab and Chemotherapy as First-Line Treatment in Subjects With Claudin18.2 Positive Locally Advanced or Metastatic Gastric or Gastroesophageal Junction (G/GEJ) Adenocarcinoma

Gastric/GEJ adenocarcinomas are aggressive tumors with a high probability of death. Current treatment guidelines include two-drug cytotoxic chemotherapy with a fluoropyrimidine (mFOLFOX6: capecitabine or fluorouracil) and a platinum-based agent (CapOx: oxaliplatin or cisplatin). In addition, the FDA has approved nivolumab, a PD-1 checkpoint inhibitor, in combination with chemotherapy as first line treatment for advanced or metastatic gastric/GEJ cancer. TST001 is a recombinant humanized monoclonal antibody against Claudin 18.2 (a tumor marker found in gastric/GEJ cancer. In this study, the combination therapy of chemotherapy or chemotherapy and pembrolizumab with and without TST001 could provide additional benefits to the management of these tumors.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

This Phase 3, randomized, double-blind, placebo-controlled study is designed to evaluate the safety and efficacy of TST001 in combination with pembrolizumab and chemotherapy or chemotherapy alone in subjects with tumors that express markers (HER2 negative, Claudin18.2 positive, known PD-L1 CPS status) in locally advanced or metastatic gastric/GEJ adenocarcinoma. Patients will be randomized in a 1:1 ration to receive TST001 or placebo in combination with nivolumab and chemotherapy or with chemotherapy alone.

Study Type

Interventional

Enrollment (Estimated)

820

Phase

  • Phase 3

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • 1. ≥18 years of age on day of signing informed consent. 2. Histologically or cytologically confirmed diagnosis of previously untreated, unresectable locally advanced or metastatic G/GEJ adenocarcinoma.

    3. Must be willing and able to provide archival or fresh tissue sample, a formalin-fixed, paraffin-embedded (FFPE) block, or 151 or more unstained, freshly cut, serial sections (on slides) from an FFPE tumor specimen or fresh biopsy tissue from a tumor lesion (either primary or metastatic) not previously irradiated fixed in formalin solution. FFPE tissue blocks are preferred to slides. Notes: details pertaining to tumor tissue submission can be found in the Laboratory Manual. Fresh biopsies are not required for study entry and will not be covered as part of the study procedures. Handling of the fresh biopsy tissue is an alternative offered to investigators in case they plan to biopsy the subjects as part of their standard of care; the fresh sample can be sent directly to the central laboratory if it is more convenient to the sites.

    4. Positive CLDN18.2 expression in tumor tissue confirmed by the central laboratory at screening using CTA (Claudin 18.2 IHC 14G11 pharmDx).

    5. Must have at least one measurable lesion or evaluable disease by CT or MRI per RECIST 1.1 criteria as assessed locally by the investigator; radiographic tumor assessment should be performed within 28 days prior to randomization.

    6. Subjects should be eligible to receive chemotherapy and pembrolizumab per the investigator judgement.

    7. Known PD-L1 CPS Status (tested by central laboratory to provide CPS status by PD-L1 IHC 22C3 pharmDx).

    8. Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 assessed within 14 days before randomization.

    9. Subjects who have AEs due to previous anticancer therapies must have recovered to ≤Grade 1 or pre-treatment status. Subjects with endocrine-related AEs who are adequately treated with hormone replacement or subjects who have ≤Grade 2 neuropathy are eligible.

    10. Have a life expectancy of greater than 12 weeks. 11. Demonstrate adequate organ function.

Exclusion Criteria

  1. Has received any prior systemic anticancer treatment (chemotherapy, immunotherapy, biologic therapy, or targeted therapy) for G/GEJ adenocarcinoma. Neo/adjuvant treatment is permitted as long as it was completed at least 6 months prior to randomization.
  2. Has received prior radiotherapy within 2 weeks before randomization; Note: Subjects must have recovered from all radiation-related toxicities. A previously irradiated lesion can be used as measurable lesion as long as it progressed post radiation therapy.
  3. Has received anti-CLDN18.2 agents at any time.
  4. Has received any traditional Chinese medicine or proprietary Chinese medicine with anti-tumor effect within 7 days before randomization.
  5. Has received vaccines (live, attenuated, or research vaccines) within 30 days before randomization. Administration of killed vaccines is allowed.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Triple

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Active Comparator: TST001 + PDL-1 + Chemotherapy
TST001 + Pembrolizumab + Chemotherapy (FOLFOX6 or CapOx)
Drug: Pembrolizumab and either Capcecitabine + Oxaliplatin or Oxaliplatin+Leucovorin + 5-fluorouracil
TST001 will be administered i.v. Q3W along with standard prescribing dose of pembrolizumab Q3W + standard prescribed regimens for FOLFOX6 or CapOx.
Drug: Pembrolizumab and either Capcecitabine + Oxaliplatin or Oxaliplatin+Leucovorin + 5-fluorouracil
Placebo will be administered i.v. Q3W along with standard prescribing dose of pembrolizumab Q3W + standard prescribed regimens for FOLFOX6 or CapOx.
Placebo Comparator: Placebo
Placebo + Pembrolizumab + Chemotherapy (FOLFOX6 or CapOx)
Drug: Pembrolizumab and either Capcecitabine + Oxaliplatin or Oxaliplatin+Leucovorin + 5-fluorouracil
TST001 will be administered i.v. Q3W along with standard prescribing dose of pembrolizumab Q3W + standard prescribed regimens for FOLFOX6 or CapOx.
Drug: Pembrolizumab and either Capcecitabine + Oxaliplatin or Oxaliplatin+Leucovorin + 5-fluorouracil
Placebo will be administered i.v. Q3W along with standard prescribing dose of pembrolizumab Q3W + standard prescribed regimens for FOLFOX6 or CapOx.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Progression free survival (PFS) based on RECIST (v1.1)
Time Frame: Date of randomization until the date of documented progression or date of death due to any cause, whichever comes first up to 24 months after last dose.
Compare PFS of patients treated with TST001 or Placebo in combination with pembrolizumab and chemotherapy
Date of randomization until the date of documented progression or date of death due to any cause, whichever comes first up to 24 months after last dose.

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Overall Survival (OS) based on RESIST
Time Frame: Time from date of randomization until the date of death due to any cause, assessed up to 24 months after last dose.
Compare OS of patients treated with TST001 or Placebo in addition to CapOx or mFOLFOX6 and pembrolizumab or CapOx or mFOLFOX6
Time from date of randomization until the date of death due to any cause, assessed up to 24 months after last dose.
Overall Response Rate (ORR) based on RESIST (v1.1)
Time Frame: Date of randomization up to 24 months after last dose
Compare OOR patients treated with TST001 or Placebo in addition to CapOx or mFOLFOX6 and pembrolizumab or CapOx or mFOLFOX6.
Date of randomization up to 24 months after last dose
Quality of Life (QOL) assessed on EuroQol EQ5D-5L
Time Frame: Date of randomization until the date of documented progression, assessed up to 24 months after last dose
Change in QOL assessments from baseline of patients treated with TST001 or Placebo in addition to mFOLFOX6 and pembrolizumab or CapOx or mFOLFOX6. Assessments include Cancer QOL questionnaires (QLC-STO22, EQ5D-5L, and QLQ-C30)
Date of randomization until the date of documented progression, assessed up to 24 months after last dose
Disease Control Rate (DCR) based on RESIST assessed as the percentage of subjects with measurable disease
Time Frame: Date of randomization up to 24 months after last dose
Compare DCR of patients treated with TST001 or Placebo in addition to CapOx or mFOLFOX6 and pembrolizumab or CapOx or mFOLFOX6.
Date of randomization up to 24 months after last dose
Duration of Response (DOR) based on RESIST (log-rank test)
Time Frame: From date of randomization up to 24 months after last dose
Compare DOR of patients treated with TST001 or Placebo in addition to CapOx or mFOLFOX6 and pembrolizumab or CapOx or mFOLFOX6.
From date of randomization up to 24 months after last dose
Time to Response (TTR) based on RESIST
Time Frame: Date of randomization up to 24 months after last dose
Compare TTR of patients treated with TST001 or Placebo in addition to CapOx or mFOLFOX6 and pembrolizumab or CapOx or mFOLFOX6 based on CR or PR.
Date of randomization up to 24 months after last dose

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Suzhou Transcenta Therapeutics Co., Ltd.

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

June 30, 2026

Primary Completion (Estimated)

October 1, 2029

Study Completion (Estimated)

January 31, 2030

Study Registration Dates

First Submitted

September 24, 2023

First Submitted That Met QC Criteria

October 16, 2023

First Posted (Actual)

October 23, 2023

Study Record Updates

Last Update Posted (Estimated)

December 17, 2025

Last Update Submitted That Met QC Criteria

December 12, 2025

Last Verified

December 1, 2025

More Information

Terms related to this study

Additional Relevant MeSH Terms

Other Study ID Numbers

  • TST001-3001

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

IPD Plan Description

Summary of study results will be available through Clinicaltrials.gov

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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