HENLIUS - VOLUNTARY ANNOUNCEMENT - THE FIRST PATIENT IN THE UNITED STATES HAS BEEN DOSED

IN AN INTERNATIONAL MULTICENTER PHASE 1 CLINICAL STUDY OF IPILIMUMAB BIOSIMILAR HLX13 (RECOMBINANT ANTI-CTLA-4 FULLY HUMAN MONOCLONAL ANTIBODY INJECTION) AS A FIRST-LINE TREATMENT FOR PATIENTS WITH UNRESECTABLE ADVANCED HEPATOCELLULAR CARCINOMA (HCC)

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 FIRST PATIENT IN THE UNITED STATES HAS BEEN DOSED IN AN INTERNATIONAL MULTICENTER PHASE 1 CLINICAL STUDY OF IPILIMUMAB BIOSIMILAR HLX13 (RECOMBINANT ANTI-CTLA-4

FULLY HUMAN MONOCLONAL ANTIBODY INJECTION) AS A FIRST- LINE TREATMENT FOR PATIENTS WITH UNRESECTABLE ADVANCED HEPATOCELLULAR CARCINOMA (HCC)

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 first patient in the United States has been dosed in an international multicenter phase 1 clinical study of Ipilimumab biosimilar HLX13 (recombinant anti-CTLA-4 fully human monoclonal antibody injection) ("HLX13") independently developed by the Company as a first-line treatment for patients with unresectable advanced hepatocellular carcinoma (HCC).

B. CLINICAL TRIAL DESIGN AND OBJECTIVES

This study is an international multicenter, randomized, double-blind, parallel-controlled

phase 1 clinical study to evaluate the pharmacokinetic (PK) characteristics, safety, efficacy, and immunogenicity of HLX13 compared with its reference product YERVOY® (US-sourced), each in combination with OPDIVO® (EU-sourced, INN: nivolumab), in patients with previously untreated, unresectable advanced hepatocellular carcinoma (HCC). Eligible subjects will be randomly assigned to two groups at a 1:1 ratio. Subjects will receive HLX13 or YERVOY® in combination with OPDIVO® once every 3 weeks for the first 4 cycles, followed by maintenance monotherapy with OPDIVO® administered every 4 weeks. The primary objective of this study is to evaluate the PK similarity of HLX13 and US-sourced YERVOY® in the target patient population. The primary endpoints are area under the serum concentration-time curve from time 0 to 21 days (AUC0-21d) after the 1st dose and the area under the serum concentration-time curve within a dosing interval at steady-state (AUCss) after the 4th dose, or area under the serum concentration-time curve from time 0 to infinity at steady-state (AUCinf) after the 4th dose. Secondary endpoints include other PK parameters,

efficacy assessments, safety and immunogenicity.

C. ABOUT HLX13

HLX13 is a biosimilar of Ipilimumab independently developed by the Company, and is intended for the indications of the reference drug such as melanoma, renal cell carcinoma, colorectal cancer, hepatocellular carcinoma, non-small cell lung cancer, malignant pleural mesothelioma and esophageal squamous cell carcinoma, etc. Ipilimumab is a fully human, anti-CTLA-4 (cytotoxic T-lymphocytes associated antigen 4, also known as CD152), IgG1 monoclonal antibody with κ light chain. By blocking the binding between CTLA-4 and the ligands, Ipilimumab can elevate the immune response and in turn achieve the goal of killing tumors. In September 2025, the investigational new drug application (IND) for the phase 1 clinical trial of HLX13 as a first-line treatment for patients with unresectable hepatocellular carcinoma (HCC) was approved by the United States Food and Drug Administration (FDA). In November 2025, the first patient has been dosed in an international multicenter phase 1 clinical study of HLX13 as a first-line treatment for patients with unresectable hepatocellular carcinoma (HCC) in Chinese Mainland (excluding Hong Kong, Macau and Taiwan regions

of China). In April 2025, the Company entered into a license agreement with Sandoz AG, pursuant to which, the Company granted an exclusive license to Sandoz AG to commercialize HLX13 within the United States, agreed European countries, Japan, Australia and Canada.

D. MARKET CONDITION

According to the information of IQVIA MIDASTM (IQVIA is a global provider of professional information and strategic consulting services in the pharmaceutical and healthcare industry), the worldwide sales of Ipilimumab in 2025 was approximately US$3.277 billion.

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 HLX13. 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, 25 June 2026