Zhitong Financial App News, Shiyao Group (01093) issued an announcement. The results of the Phase I/II clinical study of SYS6043, a novel B7 homologous 3 (ADC) targeting antibody conjugate drug (ADC) developed independently by the Group for advanced breast cancer patients (this study) were announced in the form of a quick oral report on October 26, 2026 at the 2026 European Society of Medical Oncology (ESMO) annual meeting (ID: 5RO). B7-H3 The study was reported by Professor Wang Hongxia of the Cancer Hospital Affiliated to Fudan University.
The study is a multi-center, open-label phase I/II clinical study led by Professor Zhang Li of the Cancer Center of Sun Yat-sen University and Professor Wu Lingying of the Cancer Hospital of the Chinese Academy of Medical Sciences to evaluate the safety, tolerability, pharmacokinetics and initial efficacy of SYS6043 in patients with advanced solid tumors.
This report focuses on the breast cancer cohort. As of the data cutoff date (June 15, 2026), the cohort included a total of 139 advanced breast cancer patients, including hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer (HR+/HER2-BC, n=84), triple-negative breast cancer (TNBC, n=32), and HER2 positive (HER2+) breast cancer (HER2+BC, n=23). The median age of patients was 54 years old, and most patients had previous multi-line treatment.
At this meeting, the Group announced the positive results of the study. The relevant safety and efficacy data are as follows:
Safety: SYS6043 was well tolerated overall in 139 patients receiving at least one dose. The incidence of treatment-related adverse events (TRAE) was 993%, the incidence of grade 3 or higher TRAE was 288%, and the incidence of severe TRAE was 58%. The most common TRAEs include nausea (612%), leukopenia (604%), neutropenia (554%), anemia (511%), and fatigue (511%). The proportion of patients with dose interruption and dose reduction due to TRAE was 245% and 65%, respectively. Only 1 case (07%) of patients discontinued treatment due to TRAE. There were no treatment-related deaths in this study. The incidence of interstitial lung disease (ILD) is 14%.
Efficacy: SYS6043 showed positive anti-tumor activity in all three breast cancer subtypes: HR+/HER2-BC (n=82): After 51 months of median follow-up, the confirmed objective response rate (ORR) was 537%, the disease control rate (DCR) was 927%, median duration of remission (DoR) and median progression-free survival (PFS) were not achieved; TNBC (n=32): After 65 months of median follow-up, the confirmed ORR was 750%, and the DCR was 938%, median PFS of 72 Months, median dOR of 55 months; HER2+BC (n=23): After 64 months of median follow-up, confirmed ORR was 696%, DCR was 957%, median PFS was not achieved, and median DoR was 70 months.
SYS6043 showed controlled safety and good long-lasting anti-tumor activity in patients with advanced stage breast cancer, supporting further research at a dose of 6 mg/kg every 3 weeks (Q3W).
SYS6043 is an ADC targeting B7-H3 independently developed by the Group. Its load is a topoisomerase I inhibitor, and the drug-antibody ratio (DAR) is about 6. SYS6043 uses a crystallizable gamma (Fcγ) receptor effect silencing design and a lyzable connector, which has a bystander anti-tumor effect and aims to enhance anti-tumor activity and reduce off-target toxicity. B7-H3 is highly expressed in various solid tumors and is frequently expressed in breast cancer, making it a therapeutic target with good clinical application prospects.