Alphamab's JSKN003 at 2026 ESMO: 100% ORR in First-Line Gastric Cancer Combination With KN026, Median OS 23.5 Months in Platinum-Resistant Ovarian Cancer

Before this ESMO data release, the early evidence chain for JSKN003 was already taking shape. The drug is built on the parent bispecific antibody KN026, which itself showed a favourable safety profile and promising anti-tumour activity in HER2-positive solid tumours ; a pooled analysis in platinum-resistant ovarian cancer (PROC) had been reported at academic meetings , and the 2025 results from Wu Xiaohua's team showed benefit irrespective of HER2 expression in heavily treated PROC . On the regulatory front, the FDA granted JSKN003 a Fast Track designation in ovarian cancer in October 2025 . Registries show that the gastric cancer Phase II study NCT06998771 plans to enroll 153 patients in a randomized design with ORR in the first-line population as primary endpoint, sponsored by Shanghai JMT-Bio ; the Australia Phase I NCT05494918 is completed with 62 patients（需要核查）.

The two posters presented at the 2026 ESMO Congress further enriched the dataset. In the first-line gastric cancer study JSKN003-003, as of May 9, 2026, 25 patients were enrolled (7 in cohort A, 14 in B, 4 in C) with a median follow-up of 5.2 months; confirmed ORR was 71.4%, 100% and 50.0% respectively, with all 14 patients in cohort B—combined with the parent bispecific KN026—achieving partial response. Grade ≥3 TRAE incidence was 28.6% in cohort B versus 57.1% in cohort A and 100% in cohort C, with no TRAE-related deaths; DoR, PFS and OS were not yet mature. The updated PROC pooled analysis, at a median follow-up of 20.8 months across 47 patients, showed confirmed ORR of 55.3%, DCR of 93.6%, median DoR of 9.2 months, median PFS of 8.3 months and median OS of 23.5 months, with stable efficacy across HER2 expression subgroups; grade ≥3 TRAEs were 19.1%, and all 6 ILD cases were grade 1-2.

Relative to prior materials, this update delivers two substantive advances. First, with median PFS of 7.7 months at the previous 9.3-month follow-up , the follow-up has more than doubled to 20.8 months and for the first time provides a more mature median OS of 23.5 months, materially strengthening the durability evidence. Second, cohort B's 100% ORR provides the first clinical quantification supporting synergy between an ADC and its parent antibody—KN026 monotherapy had previously shown activity signals , but quantified evidence of the combination had not been seen. The trial design in the registry is consistent with the press release description . On the commercial front, in September 2024 Alphamab granted JMT exclusive rights in mainland China while retaining manufacturing; financial terms of the deal were not disclosed. JSKN003 has received two NMPA Breakthrough Therapy designations (all-comer PROC, HER2-positive advanced colorectal cancer) plus an FDA Breakthrough Therapy designation, Orphan Drug designation and Fast Track designation.

Information still to be confirmed includes: DoR, PFS and OS in the gastric cancer study, and results from the randomized phase and control arms (including trastuzumab-based regimens)—the registry shows the study includes a trastuzumab with or without pembrolizumab control arm ; enrollment progress and data timelines for the all-comer PROC Phase III study were not disclosed. Future milestones to watch include continued enrollment and longer-term follow-up updates from both studies（需要核查）。