#ESMO2026 abstract: 🇨🇳CSPC’s HER3 ADC SYS6023 Shows Preliminary Activity in Solid Tumors, Sets RP2D at 5.5 mg/kg First-in-human Phase 1 data for SYS6023 (1028P) SYS6023 is HER3-targeting ADC carrying a topoisomerase I inhibitor payload As of March 17, 2026: - 55 patients had received at least one dose of SYS6023. - Patient population: Breast cancer (56.4%) and non-small cell lung cancer (NSCLC; 43.6%) were the predominant tumor types. - Prior treatment: Median of 3 lines (range, 1–7). - ECOG performance status: 74.5% had a score of 1. - MTD and RP2D: Both established at 5.5 mg/kg. Preliminary antitumor activity - Antitumor activity was evaluated in response-evaluable patients after a median follow-up of 4.1 months (95% CI, 2.8–5.4). - Median DoR: Not reached. - Six-month DoR rate: 87.5% (95% CI, 38.7–98.1). - OS: Data remained immature at the cutoff. Safety 3 patients experienced DLTs: - At 4.5 mg/kg: one case of Grade 3 thrombocytopenia with bleeding. - At 6.5 mg/kg: one case of Grade 4 thrombocytopenia and one case of Grade 3 febrile neutropenia. Grade ≥3 TRAEs occurred in 32 patients (58.2%). The most common included neutropenia, thrombocytopenia, leukopenia and lymphopenia. No TRAE-related deaths or treatment discontinuations were reported.