CSPC PHARMA (01093.HK): SYS6043 Phase I/II results in advanced breast cancer out, TNBC ORR at 75.0%

NewTimeSpace News: CSPC PHARMA (01093.HK) announced that the results of the Phase I/II clinical study of SYS6043, a novel B7 homologue 3 (B7-H3)-targeting antibody-drug conjugate (ADC) independently developed by the Group, in patients with advanced breast cancer were presented in a rapid oral presentation (abstract No. 5RO) at the 2026 Congress of the European Society for Medical Oncology (ESMO) on 26 October 2026, with Professor Wang Hongxia of Fudan University Shanghai Cancer Center presenting. The study was jointly led by Professor Zhang Li of Sun Yat-sen University Cancer Center and Professor Wu Lingying of the Cancer Hospital Chinese Academy of Medical Sciences, and is a multicentre, open-label Phase I/II study designed to evaluate the safety, tolerability, pharmacokinetics and preliminary efficacy of SYS6043 in patients with advanced solid tumours.

According to the announcement, the presentation focused on the breast cancer cohort. As at the data cut-off date of 15 June 2026, a total of 139 patients with advanced breast cancer were enrolled, comprising 84 patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer, 32 with triple-negative breast cancer (TNBC) and 23 with HER2-positive breast cancer; the median age was 54 and most patients had received multiple prior lines of therapy. In terms of efficacy, among patients with HR+/HER2- breast cancer (n=82), after a median follow-up of 5.1 months, the confirmed ORR was 53.7% and the disease control rate (DCR) was 92.7%, with both median duration of response (DoR) and median progression-free survival (PFS) not reached; in TNBC (n=32), after a median follow-up of 6.5 months, the ORR was 75.0% and the DCR was 93.8%, with a median PFS of 7.2 months and a median DoR of 5.5 months; in HER2-positive breast cancer (n=23), after a median follow-up of 6.4 months, the ORR was 69.6% and the DCR was 95.7%, with median PFS not reached and a median DoR of 7.0 months.

In terms of safety, among 139 patients who received at least one dose, the incidence of TRAEs was 99.3%, grade ≥3 TRAEs 28.8% and serious TRAEs 5.8%; the most common TRAEs included nausea (61.2%), leukopenia (60.4%), neutropenia (55.4%), anaemia (51.1%) and asthenia (51.1%); dose interruption and dose reduction due to TRAEs occurred in 24.5% and 6.5% of patients respectively, only one patient (0.7%) discontinued treatment and no treatment-related deaths occurred, while the incidence of interstitial lung disease (ILD) was 1.4%. The study concluded that SYS6043 demonstrated manageable safety and durable antitumour activity in previously treated patients with advanced breast cancer, supporting further study at a dose of 6 mg/kg once every three weeks (Q3W); the product carries a topoisomerase I inhibitor payload with a drug-to-antibody ratio (DAR) of approximately 6, adopts an Fc gamma receptor effector-silencing design and a cleavable linker, and has a bystander antitumour effect.