CStone's anti-PD-L1 antibody demonstrates promising antitumor activity with a complete response rate of 33.3% and a good safety profile in patients with relapsed or refractory extranodal natural killer/T-cell lymphoma

SUZHOU,China,Dec. 10,2019 -- CStone Pharmaceuticals ("CStone" or the "Company",HKEX: 2616) updated results from the CS1001-201 trial in a poster presentation at the 2019 American Society of Hematology (ASH) Annual Meeting.

CS1001-201 trial is a single-arm,multicenter Phase II clinical study designed to evaluate CS1001 monotherapy in relapsed or refractory extranodal natural killer (NK)/T-cell lymphoma (rr-ENKTL).

ENKTL is a subtype of mature T cell and NK cell lymphoma. It has a higher incidence in Asia than in Europe or North America. ENKTL is characterized by its rapid progression and poor prognosis. Currently,patients with rr-ENKTL lack effective treatment after failing an L-asparaginase-based combination chemotherapy regimen and targeted monotherapy only produces a complete response (CR) rate of below 10%.

"ENKTL accounts for approximately 6% of all lymphoma incidences,and there are vast unmet medical needs in this patient population that has failed the first-line treatment," said Dr. Frank Jiang,Chief Executive Officer and Chairman of CStone. "The CS1001-201 trial is the first clinical study of an anti-PD-L1 antibody in ENKTL worldwide. Our latest data have shown CS1001 to be well-tolerated with preliminary antitumor efficacy and survival benefit in rr-ENKTL patients. We will continue to advance this development program and hope that CS1001 will soon become a new treatment option for rr-ENKTL patients."

"CR is a critical outcome measure for the treatment of ENKTL. Studies have shown that ENKTL patients who achieved CR prior to autologous transplantations have a significantly better prognosis and longer survival than those who achieved partial response," said Dr. Jason Yang,Chief Medical Officer of CStone. "These latest results of CS1001 demonstrated a CR rate of 33.3% with durable response,an objective response rate of 43.3%,and a 1-year overall survival rate of 72.4%. These results represent a major breakthrough compared to current treatment options and support CS1001 as a potential conditioning regimen for hematopoietic stem cell transplantations."

Overview of the CS1001-201 trial

CS1001-201 is a single-arm,multicenter Phase II clinical study designed to evaluate CS1001 monotherapy in relapsed or refractory extranodal natural killer (NK)/T-cell lymphoma (rr-ENKTL).

The primary endpoint of the trial is ORR assessed by an independent radiological review committee (IRRC);

Secondary endpoints include investigator-assessed ORR; IRRC-assessed CR and PR rates,time to response,duration of response,progression-free survival; overall survival,and safety.

Results reported in the poster at the 2019 ASH Annual Meeting

As of October 8,2019,32 patients were enrolled in the study. Among them,24 patients (75.0%) had Stage IV ENKTL at screening,9 patients (28.1%) received 2 lines of prior treatments,and 7 patients (21.9%) received 3 or more lines of prior treatments. All patients received 1200 mg CS1001 intravenously every 3 weeks for up to 2 years,until disease progression,intolerance,etc. The median duration of follow-up was 6.54 months (range,0.72-15.64).

13 (40.6%) of the 32 enrolled patients remained on treatment,and 19 (59.4%) had discontinued from the study treatment.

Reasons for discontinuations included radiographic disease progression (12 patients),adverse events (AEs,4 patients),and non-radiographic symptomatic progression (3 patients).

No deaths due to treatment-related AEs (TRAEs).

Preliminary efficacy data

CS1001 demonstrated promising antitumor activity and a favorable CR rate with durable response and survival benefit in rr-ENKTL patients.

Among the 30 efficacy-evaluable patients,the investigator-assessed ORR was 43.3%.

10 patients (33.3%) achieved CR and were still in remission.

3 patients (10.0%) achieved partial response (PR),and 1 additional patient achieved PR after pseudo-progression. The median duration of response (DoR) was not reached,and the maximum DoR was 10.9+ months.

The 1-year overall survival (OS) was 72.4% (95% CI: 52.0%-85.2%).

The IRRC assessments were not available at the time of data cut-off.

Safety data

CS1001 was well tolerated in patients with rr-ENKTL

The median duration of treatment was 12.6 weeks (range,3.0-69.1).

30 patients (93.8%) reported treatment-emergent AEs (TEAEs).

24 patients (75.0%) reported TRAEs,of which 3 (9.4%) had Grade >3 TRAEs.

Grade 5 AEs were reported in 3 patients (9.4%),and none was assessed as related to CS1001.

7 patients (21.9%) reported serious AEs (SAEs). 1 case of Grade 4 sinus node dysfunction and 1 case of Grade 1 myositis were assessed as related to CS1001 by the investigator. Both patients later recovered from the SAEs.

Immune-related AEs (irAEs) were reported in 5 patients (15.6%). Except for 1 Grade 3 rash,all irAEs were Grade 1 in severity.

TEAEs that led to permanent treatment discontinuation occurred in 4 patients (12.5%).

No deaths due to AEs were assessed as related to CS1001.

About CS1001

CS1001 is an investigational monoclonal antibody directed against PD-L1 being developed by CStone. Authorized by the U.S. based Ligand Corporation,CS1001 is developed by the OMT transgenic animal platform,which can generate fully human antibodies in one step. As a fully human,full-length anti-PD-L1 monoclonal antibody,CS1001 is similar to natural G-type immune globulin 4 (IgG4) human antibody,which can reduce the risk of immunogenicity and potential toxicities,potentially representing a unique advantage over similar drugs.

CS1001 has completed a Phase I dose-escalation study in China,in which CS1001 showed good tolerability and produced sustained clinical benefits during the Phase Ia study.

CS1001 is being investigated in a number of ongoing clinical trials,including one Phase I bridging study in the U.S. In China,its clinical program includes one multi-arm Phase Ib study,two pivotal Phase II studies,and three Phase III studies for several tumor types.

About CStone

CStone Pharmaceuticals (HKEX: 2616) is a biopharmaceutical company focused on developing and commercializing innovative immuno-oncology and molecularly-targeted drugs to address 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. With combination therapies as a core strategy,the Company has built a rich oncology pipeline of 15 oncology drug candidates. Currently,five late-stage drug candidates are at or near pivotal trials. 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

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