CStone Pharmaceuticals — Director's Dealing 2026

Jun 3, 2026

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CStone Pharmaceuticals

基石藥業

(Incorporated in the Cayman Islands with limited liability)

(Stock Code: 2616)

VOLUNTARY ANNOUNCEMENT JOINT SHARE PURCHASE PLAN INITIATED BY THE DIRECTORS AND SENIOR MANAGEMENT

This announcement is made by CStone Pharmaceuticals (the "Company," together with its subsidiaries, collectively referred to as the "Group" or "CStone") on a voluntary basis.

Joint Share Purchase Plan Initiated by the Directors and Senior Management

Based on the confidence in the future development prospects of the Company and the recognition of the long-term investment value of the Company, Dr. Jianxin Yang ("Dr. Yang"), the Chief Executive Officer ("CEO"), President of R&D and Executive Director of the Company, together with other members of the board (the "Board") of directors (the "Directors") of the Company, and certain members of the senior management of the Company (the "Senior Management"), subject to compliance with the Rules Governing the Listing of Securities on the Stock Exchange of Hong Kong Limited and other applicable laws and regulations, initiate the plan for purchase of additional shares of the Company in the open market using their personal funds (the "Joint Share Purchase Plan"). The share purchases will take place from June 2026 until the commencement of the blackout period for the publication of interim results of the Group for the six months ended June 30, 2026, with the aggregate number of shares to be acquired ranging from 2,000,000 to 5,000,000 shares of the Company.

"The Joint Share Purchase Plan demonstrates the Directors and Senior Management's strong confidence in the global competitiveness of the Company's product pipeline. The current trading price does not reflect the actual value of the Company's R&D achievements." said Dr. Yang. "We will continue to accelerate the advancement of key clinical programs, including disclosing multiple important clinical updates for CS2009 (PD-1/VEGF/CTLA-4 trispecific antibody), initiating a global multicenter Phase III registrational trial for CS2009, and deliver sustained value for patients and shareholders of the Company."

Board Opinion

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The Board is of the view that the share purchases initiated by Dr. Yang, the Directors and Senior Management fully demonstrate their long-term commitment to the Company and their strong confidence in the future business prospects of the Company. The Board believes that such share purchases are in the best interests of the Company and its shareholders as a whole.

Shareholders and potential investors of the Company are advised to exercise caution when dealing in the securities of the Company.

About CStone

CStone (HKEX: 2616), established in late 2015, is an innovation-driven biopharmaceutical company focused on the research and development of therapies for oncology, immunology, inflammation, and other key disease areas. Dedicated to addressing patients' unmet medical needs in China and globally, the Company has made significant strides since its inception. To date, the Company has successfully launched 4 innovative drugs and secured approvals for 21 new drug applications covering 9 indications. The Company's pipeline is balanced by 16 promising candidates, featuring antibody-drug conjugates (ADCs), multispecific antibodies, immunotherapies and precision medicines. CStone also prides itself on a management team with comprehensive experiences and capabilities that span the entire drug development spectrum, from preclinical and translational research to clinical development, drug manufacturing, business development, and commercialization.

For more information about CStone, please visit: www.cstonepharma.com.

Forward Looking Statement

There is no assurance that any forward-looking statements regarding the business development of the Group in this announcement or any of the matters set out herein are attainable, will actually occur or will be realized or are complete or accurate. The financial and other data relating to the Group as disclosed in this announcement has also not been audited or reviewed by its auditors. Shareholders and/or potential investors of the Company are advised to exercise caution when dealing in the securities of the Company and not to place any excessive reliance on the information disclosed herein. Any shareholder or potential investor who is in doubt is advised to seek advice from professional advisors.

By Order of the Board
CStone Pharmaceuticals
Dr. Wei Li
Chairman

Suzhou, the People's Republic of China, June 3, 2026

As at the date of this announcement, the Board comprises Dr. Wei Li as Chairman and non-executive director, Dr. Jianxin Yang as executive director, Mr. Kenneth Walton Hitchner III and Mr. Edward Hu as non-executive directors, and Mr. Kenneth Howard Jarrett, Ms. Fang Xie and Ms. Catherine Yen as independent non-executive directors.