VOLUNTARY ANNOUNCEMENT - JSKN003 WAS GRANTED BREAKTHROUGH THERAPY DESIGNATION IN CHINA

Hong Kong Exchanges and Clearing Limited and The Stock Excha nge of Hong Kong Limited take no responsibility for the contents of this announcement, make no representation as to its accuracy or completeness and expressly disclaim any liability whatsoe ver for any loss howsoever arising from or in reliance upon the whole or any part of the contents of this ann ouncement. CSPC PHARMACEUTICAL GROUP LIMITED (Incorporated in Hong Kong with limited liability) (Stock Code: 1093) ʮ ̡ VOLUNTARY ANNOUNCEMENT JSKN003 WAS GRANTED BREAKTHROUGH THERAPY DESIGNATION IN CHINA The board of directors (the ‘‘Board ’’) of CSPC Pharmaceutical Group Limited (the ‘‘Company ’’, together with its subsidiaries, the ‘‘Group ’’) is pleased to announce that JSKN003, a biparatopic HER2-targeting antibody-drug conjugate co-developed by t he Company ’s subsidiary, Shanghai JMT- BIO Technology Co., Ltd., and Jiangsu Alphamab Biopharmace uticals Co., Ltd., has been granted Breakthrough Therapy Designation by the National Medical P roducts Administration (NMPA) of the People ’s Republic of China for the intended indication of monothera py for the all-comer population with platinum-resistant recurrent epithelial ovarian can cer, primary peritoneal carcinoma, or fallopian tube cancer (the ‘‘Indication ’’). Ovarian cancer ranks third in incidence among female reprod uctive system tumors in China and has the highest mortality rate among malignant tumors of the female reproductive tract, with approximately 70% of patients already in the advanced stage at the time of di agnosis. Tumor debulking surgery in combination with postoperative platinum-based chemother apy is the current mainstay of treatment. However, almost all patients eventually develop resistanc e to platinum-based therapy. For platinum- resistant patients, non-platinum mono-chemotherapy is th e primary treatment recommended by both domestic and international guidelines. Nevertheless, its efficacy is very limited, with a low objective response rate (ORR), short median progression-free surviv al (PFS) and overall survival, representing a significant unmet clinical need. Clinical studies of JSKN0 03 for the Indication have preliminarily demonstrated promising breakthroughs in efficacy, with a g ood safety profile and distinct clinical advantage over existing treatment options. A pooled analysis of two clinical studies on JSKN003 monothe rapy for platinum-resistant ovarian cancer presented at the European Society for Medical Oncolo gy (ESMO) Congress 2024 showed that a total of 50 platinum-resistant subjects were enrolled to re ceive at least one dose of JSKN003 monotherapy. Based on the results of local laboratory IHC te sting for HER2 expression, 10 were HER2 IHC 0, 20 were IHC 1+, 18 were IHC 2+, and 2 were IHC 3+; 56.0% of t he subjects had received three or more prior lines of therapy. Among the 44 efficacy evaluab le subjects, the ORR was 56.8% and – 1 – 88.6% (39/44) had tumor shrinkage. The disease control rate (DCR) was 95.5%, the median PFS data was immature, and the 6-month PFS rate was 44.7%. The ORR in su bjects with HER2 expression (IHC 1+, 2+, and 3+) was 52.8% (19/36), while the ORR in subjects wi th HER2 IHC 0 was 75.0% (6/8). Among the 50 subjects, only 5 (10.0%) subjects experienced G rade 3 or higher treatment-related adverse events (TRAEs), with the most common being diarrhea (2.0%) and anemia (2.0%); only one subject experienced TRAEs that led to permanent discontinu ation of treatment, and no treatment-related deaths occurred. These clinical data indicated that JSKN00 3 monotherapy exhibited remarkable efficacy in platinum-resistant ovarian cancer, bringing substanti al benefits across different levels of HER2 expression with a good safety profile. The Phase III clinical trial for the Indication is currently in the enrollment stage and progressing smoothly. JSKN003 is also undergoing multiple Phase II and I II clinical trials in China for the treatment of solid tumors, including breast cancer, gastri c cancer, colorectal cancer, and cholangiocarcinoma. The Breakthrough Therapy Designatio n granted to JSKN003 will further expedite its development and review process, making it potentially b ecome the first anti-HER2 drug for the treatment of all-comer patients with platinum-resistant o varian cancer. By order of the Board CSPC Pharmaceutical Group Limited CAI Dongchen Chairman Hong Kong, 18 March 2025 As at the date of this announcement, the Board comprises Mr. C AI Dongchen, Mr. ZHANG Cuilong, Mr. WANG Zhenguo, Mr. PAN Weidong, Mr. WANG Huaiyu, Dr. LI Chu nlei, Dr. YAO Bing, Mr. CAI Xin and Mr. CHEN Weiping as executive directors; and Mr. WANG Bo, Mr. CHEN Chuan, Prof. WANG Hongguang, Mr. AU Chun Kwok Alan, Mr. LAW Cheuk Kin Steph en and Ms. LI Quan as independent non-executive directors. – 2 –

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