HENLIUS - VOLUNTARY ANNOUNCEMENT -

THE PHASE 1 CLINICAL TRIAL OF HLX3902 INJECTION (STEAP1xCD3xCD28 TRISPECIFIC ANTIBODY) FOR THE TREATMENT OF METASTATIC CASTRATION-RESISTANT PROSTATE CANCER AND OTHER ADVANCED SOLID TUMORS HAS BEEN APPROVED TO COMMENCE IN AUSTRALIA

Shanghai Henlius Biotech, Inc.

上海復宏漢霖生物技術股份有限公司

(A joint stock company incorporated in the People's Republic of China with limited liability)

(Stock code: 2696)

VOLUNTARY ANNOUNCEMENT

THE PHASE 1 CLINICAL TRIAL OF HLX3902 INJECTION

(STEAP1×CD3×CD28 TRISPECIFIC ANTIBODY) FOR THE TREATMENT OF METASTATIC CASTRATION-RESISTANT PROSTATE CANCER AND OTHER ADVANCED SOLID TUMORS HAS BEEN APPROVED TO

COMMENCE IN AUSTRALIA

A. INTRODUCTION

This announcement is made by Shanghai Henlius Biotech, Inc. (the "Company") on a voluntary basis to inform the shareholders and potential investors of the Company about the latest business development of the Company.

The board of directors of the Company (the "Board") is pleased to announce that recently, the phase 1 clinical trial application (IND) for HLX3902 injection (STEAP1×CD3×CD28 trispecific antibody) ("HLX3902"), independently developed by the Company, for the treatment of metastatic castration-resistant prostate cancer (mCRPC) and other advanced solid tumors has been approved by the relevant Human Research Ethics Committee and acknowledged by the Therapeutic Goods Administration (TGA) of Australia.

B. ABOUT HLX3902

HLX3902 is a trispecific antibody drug independently developed by the Company, intended for the treatment of metastatic castration-resistant prostate cancer (mCRPC) and other advanced solid tumors. HLX3902 is a trispecific T-cell engager (TCE) antibody that concurrently targets STEAP1, CD3, and CD28. Through engaging CD3 and CD28 to redirect and enhance cytotoxic T cell responses to lyse STEAP1-expressing tumor cells while increasing T cell activation, proliferation, and survival via optimization of "Signal 1" (CD3) and "Signal 2" (CD28), HLX3902 can achieve the purpose of treating metastatic castration-resistant prostate cancer (mCRPC) and other advanced solid tumors. Preclinical studies have demonstrated that HLX3902 exhibits good anti-tumor efficacy and safety, and is expected to provide clinical benefits.

C. MARKET CONDITION

As of the date of this announcement, no trispecific antibody targeting STEAP1, CD3 and

CD28 has been approved globally.

WARNING STATEMENT WITH REFERENCE TO THE REQUIREMENTS UNDER RULE 18A.05 OF THE RULES GOVERNING THE LISTING OF SECURITIES ON THE STOCK

EXCHANGE OF HONG KONG LIMITED: The Company cannot guarantee the successful development and commercialization of HLX3902. Shareholders and potential investors of the Company are advised to exercise caution when dealing in the shares of the Company.

On behalf of the Board

Shanghai Henlius Biotech, Inc. Wenjie Zhang

Chairman

Hong Kong, 21 May 2026