Alphamab Oncology (Alphamab) released updated Phase I results for its bispecific antibody-drug conjugate JSKN016 at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting. The therapy targets both TROP2 and HER3 and is being evaluated in the open-label, multi-centre JSKN016-101 study in China.

Study design • Six dose levels (0.5–8 mg/kg, Q3W) were tested in dose escalation; the maximum tolerated dose was not reached. • The recommended Phase II dose (RP2D) for breast cancer was set at 6 mg/kg Q3W.

Patient profile (data cut-off: 22 Dec 2025) • 82 patients with HER2- locally advanced or metastatic breast cancer (BC) were enrolled: 50 with triple-negative BC (TNBC) and 32 with hormone-receptor-positive/HER2- (HR+/HER2-) disease. • 98.8% had stage IV disease; 7.3% had brain metastases. • All TNBC patients had prior taxane exposure; 28% had ≥3 previous systemic regimens. All HR+/HER2- patients had progressed after endocrine therapy plus CDK4/6 inhibition and at least one chemotherapy line.

Efficacy at RP2D • As of 22 Dec 2025: – TNBC (n=31): investigator-assessed objective response rate (ORR) 64.5%; median progression-free survival (mPFS) 7.6 months. – HR+/HER2- (n=29): investigator-assessed ORR 51.7%; mPFS not yet mature. • Extended cut-off (17 Mar 2026) showed durability: – TNBC: ORR unchanged at 64.5%; disease control rate (DCR) 83.9%; mPFS 8.5 months (95% CI: 4.11–10.02). – HR+/HER2-: ORR 51.7%; DCR 100%; 12-month PFS rate 61.7%; mPFS not yet mature.

Safety (cut-off: 17 Mar 2026; median follow-up 7.8 months) • Grade ≥3 treatment-related adverse events (TRAEs) occurred in 24.6% of patients; no grade 4/5 TRAEs, treatment-related deaths or interstitial lung disease were observed. • Serious adverse events were reported in 15.4% of patients (12.3% treatment-related). • Dose reductions due to TRAEs occurred in 46.2%; permanent discontinuation was 1.5% (one case of grade 3 conjunctivitis). • Most frequent grade 3 TRAEs included decreased neutrophil count (7.7%), decreased white blood cell count (6.2%), elevated amylase (4.6%) and stomatitis (4.6%).

Next steps The encouraging efficacy and manageable safety profile support ongoing Phase II trials of JSKN016 as monotherapy and in combination regimens across breast and lung cancer, as well as a Phase III study in TNBC.