– ASP2138’s advancement into Phase 3 marks an important milestone in Astellas’ commitment to advancing research in CLDN18.2 with its differentiated portfolio, spanning approved treatments and investigational assets – 

TOKYO, Aug. 24, 2026 /PRNewswire/ — Astellas Pharma Inc. (TSE: 4503, President and CEO: Naoki Okamura, “Astellas”) today announced that the first patient has been dosed in a Phase 3 study evaluating ASP2138 in combination with chemotherapy and pembrolizumab as first-line treatment in adults with locally advanced unresectable or metastatic gastric or gastroesophageal junction (GEJ) adenocarcinoma, whose tumors are Claudin 18.2 (CLDN18.2)-positive and HER2-negative.¹

This milestone marks an important step in Astellas’ commitment to advancing CLDN18.2 science through a portfolio of approved treatments and investigational assets.

Despite recent advances, many people with advanced gastric and GEJ cancers continue to face poor outcomes, with median progression-free survival of 6 to 7 months with non-CLDN18.2 directed current standard of care.² Recognizing the importance of continued research into new treatments, Astellas is working to deepen understanding of CLDN18.2 and exploring multiple scientific approaches that may help address different patient needs.

ASP2138 is an investigational subcutaneously administered bispecific antibody designed to bind to CLDN18.2, a protein expressed on certain tumor cells, and CD3-positive T cells, a type of white blood cell with the ability to kill cancer cells.^1,3 By binding to both targets, ASP2138 is intended to bring these T cells closer to CLDN18.2-expressing tumor cells and activate their anti-tumor response.⁴

Tadaaki Taniguchi, M.D., Ph.D., Chief Research and Development Officer, Astellas:
“The first patient dosed in this Phase 3 study is an important milestone for ASP2138 and for our broader work in CLDN18.2. By advancing multiple scientific approaches, we are building the evidence needed to better understand how CLDN18.2-targeted innovation may help address patient needs.”

As Astellas’ lead program within its Immuno-Oncology Primary Focus, the ASP2138 Phase 3 study supports the Company’s execution of its Corporate Strategic Plan, including its ambition to initiate five or more Phase 3 or pivotal studies by fiscal year 2027. Astellas will share updates as the study progresses, in line with applicable disclosure requirements and company practice.

About Astellas’ Corporate Strategic Plan
Learn more at www.astellas.com/en/about/corporate-strategic-plan.

About CLDN18.2 in Gastric Cancer
Claudin 18.2 (CLDN18.2) is a tight junction protein that is normally expressed in gastric mucosal cells and can remain expressed in certain gastric and gastroesophageal junction (GEJ) cancers. CLDN18.2 has emerged as an important therapeutic target in gastric cancer, leading to growing interest in developing treatment approaches designed to target tumors expressing this biomarker.

Astellas is committed to advancing research in CLDN18.2-positive cancers through a differentiated portfolio of approved and investigational assets. By exploring multiple scientific modalities and mechanisms of action, Astellas aims to deepen understanding of CLDN18.2 and help address the evolving needs of people living with gastric cancer.

About ASP2138 
ASP2138 is an investigational subcutaneously administered bispecific antibody designed to bind to CLDN18.2, a protein expressed on certain tumor cells, and CD3-positive T cells, a type of white blood cell with the ability to kill cancer cells.^1,3 By binding to both targets, ASP2138 is intended to bring these T cells closer to CLDN18.2-expressing tumor cells and activate their anti-tumor response.⁴ For more information about the Phase 3 study, visit ClinicalTrials.gov and search for identifier NCT07673887.

The safety and efficacy of ASP2138 have not been established for the uses being considered. There is no guarantee that ASP2138 will receive regulatory approval and become commercially available for the uses being investigated.

About the Study¹
The Phase 3, randomized, double-blind, placebo-controlled study is designed to evaluate the efficacy and safety of ASP2138 plus chemotherapy (CAPOX or mFOLFOX6) with pembrolizumab versus placebo plus chemotherapy with or without pembrolizumab as first-line treatment in participants with locally advanced unresectable or metastatic gastric or GEJ adenocarcinoma whose tumors are CLDN18.2-positive and HER2-negative. The co-primary endpoints are overall survival and progression-free survival. The study plans to enroll 570 participants across multiple countries.

About Astellas
Astellas is a global life sciences company committed to turning innovative science into value for patients. We provide transformative therapies in disease areas that include oncology, ophthalmology, urology, immunology and women’s health. Through our research and development programs, we are pioneering new healthcare solutions for diseases with high unmet medical need. Learn more at www.astellas.com.

Cautionary Notes
In this press release, statements made with respect to current plans, estimates, strategies and beliefs and other statements that are not historical facts are forward-looking statements about the future performance of Astellas. These statements are based on management’s current assumptions and beliefs in light of the information currently available to it and involve known and unknown risks and uncertainties. A number of factors could cause actual results to differ materially from those discussed in the forward-looking statements. Such factors include, but are not limited to: (i) changes in general economic conditions, and in laws and regulations, relating to pharmaceutical markets, (ii) currency exchange rate fluctuations, (iii) delays in new product launches, (iv) the inability of Astellas to market existing and new products effectively, (v) the inability of Astellas to continue to effectively research and develop products accepted by customers in highly competitive markets, and (vi) infringements of Astellas’ intellectual property rights by third parties. Information about pharmaceutical products (including products currently in development) which is included in this press release is not intended to constitute an advertisement or medical advice.

References

1. U.S. National Library of Medicine. A phase 3, global, multi-center, double-blind, randomized study of ASP2138 plus chemotherapy (CAPOX or mFOLFOX6) with pembrolizumab vs placebo plus chemotherapy with or without pembrolizumab in first-line treatment of locally advanced unresectable or metastatic gastric or gastroesophageal junction (GEJ) adenocarcinoma in participants whose tumors are HER2-negative and claudin (CLDN) 18.2-positive. ClinicalTrials.gov. Identifier: NCT07673887. [Online] Available at http://clinicaltrials.gov/study/NCT07673887. Accessed August 2026.
2. Rha SY, Oh DY, Yañez P, Bai Y, Ryu MH, Lee J, et al. Pembrolizumab plus chemotherapy versus placebo plus chemotherapy for HER2-negative advanced gastric cancer (KEYNOTE-859): a multicentre, randomised, double-blind, phase 3 trial. Lancet Oncol. 2023;24(11):1181-1195. doi:10.1016/S1470-2045(23)00515-6.
3. Dayyani F, Strickler JH, Hara K, et al. ASP2138 monotherapy or in combination with pembrolizumab and mFOLFOX6 or with ramucirumab and paclitaxel in claudin 18 isoform 2 (CLDN18.2)+ locally advanced unresectable or metastatic gastric or gastroesophageal junction adenocarcinoma: Phase I/Ib trial. Annals of Oncology. 2025;36(Suppl 2):S1120. doi:10.1016/j.annonc.2025.08.2755.
4. U.S. National Cancer Institute. Anti-CLDN18.2/anti-CD3 bispecific antibody ASP2138. NCI Drug Dictionary. [Online] Available at: https://www.cancer.gov/publications/dictionaries/cancer-drug/def/anti-cldn182-anti-cd3-bispecific-antibody-asp2138 Accessed August 2026.

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SOURCE Astellas Pharma Inc.