– Overall Response Rate of 78%, CR+CRh Rate of 65% and 12-month Survival Rate of 82% –

– With Longer Follow Up Data, CR Rate Increased to 57% with Majority of Patients with CR Achieving IDH1 Mutation Clearance –

– Mean Neutrophil and Platelet Counts Were Maintained Near or Above CRh Thresholds While on Study Treatment–

– Safety Profile of Combination Therapy Remains Consistent with Safety Profile of Ivosidenib and Azacitidine Alone in This Patient Population –

Suzhou, CHina, Mar 7, 2019 – CStone partner Agios Pharmaceuticals, Inc. (NASDAQ:AGIO) recently presented updated data from a Phase 1 study evaluating ivosidenib (TIBSOVO^®; AG-120) in combination with azacitidine in newly diagnosed isocitrate dehydrogenase-1 (IDH1) mutant acute myeloid leukemia (AML) patients. CStone is responsible for ivosidenib's development and commercialization in Greater China Region under an exclusive collaboration and license agreement with Agios.

“With longer follow up from the ongoing Phase 1 study, the ivosidenib and azacitidine combination data in newly diagnosed AML patients are striking, with a 65% CR+CRh rate, 57% CR rate and the majority of CR patients achieving IDH1 mutation clearance,” said Courtney DiNardo, M.D., lead investigator and assistant professor, department of leukemia at the University of Texas MD Anderson Cancer Center. “The combination regimen showed a 12-month survival rate of 82%, which is impressive given the age and comorbidities associated with patients who are not eligible for intensive chemotherapy. From a safety perspective, results from the combination were consistent with the safety profiles of each drug used alone and cytopenias were in line with those seen for azacitidine alone and favorable compared with other emerging hypomethylating agent combinations.”

“As the Phase 1 data have matured, we saw an increase in patients achieving deep and durable remissions, validating our belief that the combination of azacitidine and ivosidenib has the potential to be a compelling treatment option and the cornerstone of therapy for frontline AML patients with an IDH1 mutation who are ineligible for intensive chemotherapy,” said Chris Bowden, M.D., chief medical officer at Agios. “We will further evaluate the clinical benefit of ivosidenib in this treatment combination as part of the ongoing Phase 3 AGILE trial.”

About the Ongoing Phase 1/2 Study
The ongoing Phase 1/2 study is evaluating an investigational use of ivosidenib or enasidenib in combination with azacitidine in patients with newly diagnosed IDH mutant AML unable to receive intensive chemotherapy. Data presented are from the ivosidenib arm of the Phase 1b portion of the study, in which 23 patients received 500 mg of ivosidenib daily plus azacitidine. Enrollment in the ivosidenib arm is complete.

• As of the August 1, 2018 data cutoff, 14 (61%) patients remained on study.
• The median number of treatment cycles was 8 (range 1-22).
• The median age was 76 years old, and 52% of patients were age 75 or older.
• 74% of patients had de novo AML and 26% had secondary AML.

Ivosidenib Safety

• The most common all-grade adverse events (AEs) regardless of cause occurring in ≥50% of patients were nausea (61%), diarrhea (57%), anemia (52%) and thrombocytopenia (52%).
• The most common Grade 3/4 AEs were thrombocytopenia (48%), anemia (44%) and febrile neutropenia (44%).
• Investigator reported IDH differentiation syndrome (DS) was reported in four patients, of which three were serious AEs. All four cases resolved, including two who achieved a complete response (CR), one stable disease and one was not evaluable for response.
• Mean neutrophil and platelet counts were maintained near or above thresholds for CR with partial hematologic recovery (CRh) while on study treatment with ivosidenib and azacitidine. CRh is defined as <5% of blasts in the bone marrow, no evidence of disease and partial recovery of peripheral blood counts (ANC >500/microliter and platelets >50,000/microliter).

Ivosidenib Efficacy

• Overall, 78% (18/23) of patients had a response.
• 65% (15/23) of patients had a CR+CRh
• 57% (13/23) of patients had a CR.
• The median duration of CR (95% CI 7.7, NE) as well as CR+CRh (95% CI 7.7, NE) had not been reached.
• The median time to response was 1.8 months (range 0.7-3.8 months) and the median time to CR was 3.5 months (range 0.8-6 months).
• The 12-month survival rate was 82%.
• The median duration of follow-up was 9.5 months (range 1.3-24 months).
• For patients who achieved a CR, IDH1 mutation clearance was observed in 9 of 13 patients with available bone marrow mononuclear cells (BMMCs) and 10 of 13 patients with available peripheral blood mononuclear cells (PBMCs) as quantified by a sensitive digital PCR assay with lower limit of sensitivity for mutant IDH1 of 0.02-0.04% (or 10^-4).

Ivosidenib is not approved in any country for the treatment of patients with newly diagnosed AML or approved in combination with azacitidine.

About TIBSOVO^® (ivosidenib)

TIBSOVO^® (ivosidenib) is an isocitrate dehydrogenase-1 (IDH1) inhibitor indicated for the treatment of adult patients with relapsed or refractory acute myeloid leukemia (AML) with a susceptible IDH1 mutation as detected by an FDA-approved test. For more information, visit TIBSOVO.com.

About Acute Myelogenous Leukemia (AML)
AML, a cancer of blood and bone marrow characterized by rapid disease progression, is the most common acute leukemia affecting adults. Undifferentiated blast cells proliferate in the bone marrow rather than mature into normal blood cells. AML incidence significantly increases with age, and the median age of diagnosis is 68. The vast majority of patients do not respond to chemotherapy and progress to relapsed/refractory AML. The five-year survival rate for AML is approximately 27 percent. IDH1 mutations are present in about 6 to 10 percent of AML cases.

About CStone

CStone Pharmaceuticals is a biopharmaceutical company focused on developing and commercializing innovative immuno-oncology and molecularly targeted drugs to address significant unmet medical needs for cancer patients in China and worldwide. Since the Company's inception in 2015, CStone has assembled a world-class management team that has a full spectrum of complementary skillsets from preclinical research to clinical development and commercialization. Through dual sources of innovation, comprised of internal research and external partnership, the Company has built a rich oncology pipeline of 14 oncology drug candidates with significant mono- and combination-therapy potential and synergies, including 4 assets exclusively in-licensed in Greater China from Agios and Blueprint Medicines. Among CStone's portfolio, 4 late-stage drug candidates are at or near pivotal trials. CStone's business model has a clear focus on clinical development, while at the same time, the Company is rapidly developing its commercial and manufacturing capabilities. The Company is backed by prestigious VC and PE funds with record-breaking amounts of equity investment, raising a combined total of approximately USD 412 million in two pre-IPO financing rounds. With an experienced team, a rich pipeline, a robust clinical development-driven business model, and substantial funding, CStone's vision is to become globally recognized as a leading Chinese biopharmaceutical company by bringing innovative and differentiated oncology therapies to cancer patients worldwide.

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

About Agios
Agios is focused on discovering and developing novel investigational medicines to treat cancer and rare genetic diseases through scientific leadership in the field of cellular metabolism. In addition to an active research and discovery pipeline across both therapeutic areas, Agios has two approved oncology precision medicines and multiple first-in-class investigational therapies in clinical and/or preclinical development. All Agios programs focus on genetically identified patient populations, leveraging our knowledge of metabolism, biology and genomics. For more information, please visit the company's website at www.agios.com.