HENLIUS - VOLUNTARY ANNOUNCEMENT - THE FIRST PATIENT HAS BEEN DOSED IN A PHASE 1 CLINICAL STUDY OF CETUXIMAB INJECTION BIOSIMILAR HLX05-N (RECOMBINANT ANTI-EGFR CHIMERIC HUMAN-MURINE MONOCLONAL ANTIBODY INJECTION) IN PATIENTS WITH METASTATIC COLORECTAL CANCER (mCRC) IN CHINESE MAINLAND

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 HAS BEEN DOSED IN A PHASE 1 CLINICAL STUDY OF CETUXIMAB INJECTION BIOSIMILAR HLX05-N (RECOMBINANT

ANTI-EGFR CHIMERIC HUMAN-MURINE MONOCLONAL ANTIBODY INJECTION) IN PATIENTS WITH METASTATIC COLORECTAL CANCER (mCRC) IN CHINESE MAINLAND

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 has been dosed in a phase 1 clinical study of cetuximab injection biosimilar HLX05-N (recombinant anti-EGFR chimeric human-murine monoclonal antibody injection) ("HLX05-N") independently developed by the Company in patients with metastatic colorectal cancer (mCRC) in Chinese Mainland (excluding Hong Kong, Macau and Taiwan regions).

B. CLINICAL TRIAL DESIGN AND OBJECTIVES

This study is a multicenter, randomized, double-blind, parallel-controlled phase 1 clinical study comparing HLX05-N with US- and EU-sourced Erbitux®, each in combination with chemotherapy (mFOLFOX6), in participants with metastatic colorectal cancer characterized by wild-type KRAS/NRAS and no BRAF V600E mutation. Participants will be randomized in a 1:1:1 ratio to the HLX05-N, US-sourced Erbitux®, or EU-sourced Erbitux® group, with stratification by ECOG performance status and gender. During the first 3 cycles, participants will receive the assigned study drug in combination with chemotherapy. Thereafter, participants in the US- or EU-sourced Erbitux® groups will switch to HLX05-N under blinded conditions and continue combination chemotherapy until a protocol-defined discontinuation criterion is met. The primary objective of this study is to evaluate the pharmacokinetic similarity between HLX05-N and Erbitux® following single and multiple intravenous infusions. The secondary objective is to compare their pharmacokinetic characteristics,

efficacy, safety, and immunogenicity.

C. ABOUT HLX05-N

HLX05-N is a cetuximab injection biosimilar independently developed by the Company, intended for the treatment of metastatic colorectal cancer and head and neck squamous cell carcinoma. Epidermal Growth Factor Receptor (EGFR) is a transmembrane glycoprotein expressed in both normal epithelial tissues and various tumor tissues, including colorectal cancer and head and neck cancer. Cetuximab specifically binds to EGFR in both normal and tumor cells, competitively inhibiting the binding of ligands such as EGF. This binding blocks receptor phosphorylation and the activation of associated kinases, thereby inhibiting cell growth, inducing apoptosis, and reducing the production of matrix metalloproteinases and vascular endothelial growth factor. While EGFR activates wild-type RAS proteins through signal transduction, it is ineffective against RAS-mutant cells. Furthermore, cetuximab exerts antitumor effects on certain tumors through antibody-dependent cellular cytotoxicity (ADCC). In accordance with the requirements of the biosimilar guidelines issued by the National Medical Products Administration (NMPA), and with reference to the biosimilar

guidelines of the European Union and the United States, pharmaceutical and non-clinical comparative studies have demonstrated that HLX05-N is similar to the reference cetuximab injection. In April and May 2026, the investigational new drug applications (IND) for the phase 1 clinical trial of HLX05-N for metastatic colorectal cancer (mCRC) were approved by the National Medical Products Administration (NMPA) and the United States Food and Drug Administration (FDA), respectively.

D. MARKET CONDITION

According to the statistics released by IQVIA MIDASTM (IQVIA is a global provider of professional information and strategic consulting services in the pharmaceutical and healthcare industry), the sales revenues of cetuximab injection globally amounted to approximately USD1.658 billion in 2025.

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 HLX05-N. 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, 8 July 2026