CStone Pharmaceuticals — Capital/Financing Update 2021

Apr 26, 2021

Hong Kong Exchanges and Clearing Limited and The Stock Exchange 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 whatsoever for any loss howsoever arising from or in reliance upon the whole or any part of the contents of this announcement.

The forward-looking statements made in this announcement relate only to the events or information as of the date on which the statements are made in this announcement. Except as required by law, we undertake no obligation to update or revise publicly any forward-looking statements, whether as a result of new information, future events or otherwise, after the date on which the statements are made or to reflect the occurrence of unanticipated events. You should read this announcement completely and with the understanding that our actual future results or performance may be materially different from what we expect. In this announcement, statements of, or references to, our intentions or those of any of our directors and/or our Company are made as of the date of this announcement. Any of these intentions may alter in light of future development.

==> picture [126 x 49] intentionally omitted <==

CStone Pharmaceuticals 基石藥業

(Incorporated in the Cayman Islands with limited liability) ( Stock Code: 2616 )

VOLUNTARY ANNOUNCEMENT

NMPA ACCEPTANCE OF NDA OF SELECTIVE RET INHIBITOR GAVRETO[® ] (PRALSETINIB) WITH PRIORITY REVIEW DESIGNATION FOR THE TREATMENT OF ADVANCED OR METASTATIC RET-ALTERED THYROID CANCER PATIENTS

CStone Pharmaceuticals (the “ Company ” or “ CStone ”) is pleased to announce that the National Medical Products Administration (the “ NMPA ”) of China has accepted the New Drug Application (the “ NDA ”) of selective inhibitor GAVRETO[®] (Pralsetinib) with priority review designation for the treatment of the patients with advanced or metastatic RET-altered thyroid cancer. This may expand the labeled indications for GAVRETO[®] in China to include advanced or metastatic RET-mutant medullary thyroid cancer (“ MTC ”) who require systemic therapy, or with advanced or metastatic RET fusion-positive thyroid cancer who require systemic therapy and radioactive iodine-refractory (if radioactive iodine is appropriate).

In March 2021, the NMPA granted approval of pralsetinib under the brand name GAVRETO[®] for the treatment of adult patients with locally advanced or metastatic RET fusion-positive non-small cell lung cancer (“ NSCLC ”) after platinum-based chemotherapy. Discovered by CStone’s partner Blueprint Medicines Corporation (NASDAQ: BPMC) (“ Blueprint Medicines ”), GAVRETO[®] is the first approved selective RET inhibitor in China.

Dr. Jason Yang, Chief Medical Officer of CStone, said: “We are excited to see that this NDA has been accepted by the NMPA, which is six months in advance of our schedule. There has been a lack of precision medicines for RET-altered thyroid cancer in China and patients can only be treated with multitargeted drugs. Study results showed that GAVRETO[®] had robust and durable efficacy and a welltolerated safety profile among patients with RET-mutant MTC and RET fusion-positive thyroid cancer. We thank the NMPA for granting priority review for this indication and look forward to getting approval and hope benefit more patients in China in the future.”

1

This NDA acceptance is based on the results from the global Phase 1/2 ARROW trial, designed to evaluate the safety, tolerance and efficacy of pralsetinib in patients with RET fusion-positive NSCLC, RET-mutant MTC, and other advanced solid tumors with RET fusions.

In September 2020, results from the ARROW trial in patients with RET-mutant MTC were presented at the European Society for Medical Oncology Virtual Congress. As of a data cutoff date of February 13, 2020, the results showed that pralsetinib had robust and durable anti-tumor activity in responseevaluable patients who received a starting dose of 400 mg once daily. In 53 patients previously treated with cabozantinib or vandetanib, the overall response rate (“ ORR ”) was 60 percent (95% CI: 46%, 74%) with one response pending confirmation, and the median duration of response (“ DOR ”) was not reached (95% CI: not reached, not reached). In 19 systemic treatment-naïve patients who were ineligible for standard therapy per the study protocol, the confirmed ORR was 74 percent (95% CI: 49%, 91%), and the median DOR was not reached (95% CI: 7 months, not reached). In 438 ARROW trial patients across RET-altered tumor types, the most common treatment-related adverse events reported by investigators (≥ 15 percent) were increased aspartate aminotransferase, anemia, increased alanine aminotransferase, hypertension, constipation, decreased white blood cell count, neutropenia, decreased neutrophil count and hyperphosphatemia.

CStone has an exclusive collaboration and license agreement with Blueprint Medicines for the development and commercialization of GAVRETO[®] in Mainland China, Hong Kong, Macau, and Taiwan (the “ Greater China ”).

About Thyroid Cancer

Thyroid cancer is the most common endocrine malignancy with significantly increasing incidence in recent years. According to the data released by the National Cancer Center in 2019, the incidence of thyroid cancer ranked 4th among all malignant tumors in female in urban areas and 7th among all cancer types in China. There are about 90,000 new cases of thyroid cancer and about 6,800 deaths each year in China. Thyroid cancer is clinically divided into papillary cancer, follicular cancer, undifferentiated cancer, and medullary cancer and so on. The treatment and prognosis of different types of thyroid cancer vary according to the characteristics of the tumor.

RET fusions and mutations are key disease drivers in many cancer types (including NSCLC and several types of thyroid cancer). Approximately 10-20% of patients with papillary thyroid cancer (the most common type of thyroid cancer) carry RET fusions, and approximately 50-90% of patients with advanced MTC (approximately 2-5% of thyroid cancers) carry RET mutations. There is currently no effective approved standard treatment regimen for patients with RET-mutant MTC in China.

About GAVRETO[®] (pralsetinib)

GAVRETO [®] (pralsetinib) is a once-daily oral targeted therapy approved by the NMPA of China for the treatment of adults with locally advanced or metastatic rearranged during transfection (RET) fusion-positive NSCLC after platinum-based chemotherapy.

GAVRETO [®] has been approved by the United States (“ U.S. ”) Food and Drug Administration (“ FDA ”) for the treatment of adult patients with metastatic RET fusion-positive NSCLC as detected by an FDA approved test, adult and pediatric patients 12 years of age and older with advanced or metastatic RET-mutant MTC, and adult and pediatric patients 12 years of age and older with advanced or metastatic RET fusion-positive thyroid cancer who require systemic therapy and who are radioactive iodine-refractory (if radioactive iodine is appropriate).

GAVRETO [®] is not approved for the treatment of any other indication in China by the NMPA or in the U.S.

2

by the FDA, or for any indication in any other jurisdiction by any other health authority.

GAVRETO [®] is designed to selectively and potently target oncogenic RET alterations, including secondary RET mutations predicted to drive resistance to treatment. In preclinical studies, GAVRETO [®] inhibited RET at lower concentrations than other pharmacologically relevant kinases, including VEGFR2, FGFR2, and JAK2.

Blueprint Medicines and Roche are co-developing GAVRETO [®] globally (excluding Greater China) for the treatment of patients with RET-altered NSCLC, thyroid cancer, and other solid tumors. Blueprint Medicines and Genentech, a member of the Roche Group, are co-commercializing GAVRETO [®] in the U.S., and Roche has exclusive commercialization rights for GAVRETO [®] outside of the U.S. (excluding Greater China). The European Medicines Agency validated a marketing authorization application for GAVRETO [®] for the treatment of RET fusion-positive NSCLC, and the review is ongoing. The FDA granted breakthrough therapy designation to GAVRETO [®] for the treatment of RET fusion-positive NSCLC that has progressed following platinum-based chemotherapy and for RET mutation-positive MTC that requires systemic treatment and for which there are no alternative treatments.

About CStone

CStone is a biopharmaceutical company focused on the development and commercialization of innovative tumor immunotherapy and precision medicines to meet the ardent medical needs of cancer patients in China and worldwide. Established at the end of 2015, CStone has assembled a world-class management team with extensive experience in innovative drug development, clinical research, and commercialization. With a strategic emphasis on immuno-oncology combination therapies, the Company has built an oncology-focused pipeline of 14 drug candidates. Currently, two products have been approved by China NMPA and multiple late-stage candidates are at pivotal clinical trials or registration stages. CStone’s vision is to become a worldrenowned biopharmaceutical company leading the way to conquering cancer.

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

By order of the Board CStone Pharmaceuticals Dr. Frank Ningjun Jiang Chairman

Suzhou, People’s Republic of China, April 26, 2021

As at the date of this announcement, the Board of Directors of the Company comprises Dr. Frank Ningjun Jiang as Chairman and Executive Director, Dr. Wei Li, Mr. Qun Zhao, Mr. Yanling Cao, Mr. Xianghong Lin and Dr. Lian Yong Chen as non-executive Directors, and Dr. Paul Herbert Chew, Mr. Ting Yuk Anthony Wu and Mr. Hongbin Sun as independent non-executive Directors.

3