Alphamab Oncology pursuant to Rule 13.09(2)(a) of the Rules Governing the Listing of Securities on The Stock Exchange of Hong Kong Limited (the "Listing Rules") and the inside information provision (as defined in the Listing Rules) under Part XIVA of the Securities and Futures Ordinance (Cap. 571 of the Laws of Hong Kong). JSKN003-101 is an open-label, multi-center, dose-escalation phase I clinical trial in Australia designated to evaluate the safety, tolerability, and preliminary efficacy of JSKN003 as well as to determine the RP2D of JSKN003 in the treatment of advanced solid tumors, which was divided into two stages, being the dose-escalation stage and the dose-expansion stage.

This clinical trial has completed the first patient dosed successfully in September 2022 and the dose-escalation stage in October 2023, and enrolled 32 subjects in total. The Board announced that the preliminary efficacy and promising tolerability of JSKN003 have been demonstrated in JSKN003-101, the details of which are presented as follows: Among the 32 enrolled patients in the dose-escalation stage, who have received multi-line treatment of HER2-expressing solid tumors, the median number of lines of therapy for the enrolled patients was 3 (from 1 to 9 line(s)), of which 7 patients (21.9%) were treated with trastuzumab and 5 patients (15.6%) with HER2-high expressing BC were treated with T-DM1. The median age was 65 years old (aged from 30 to 79) and the median dosing cycle was 5 cycles (from 1 to 18 cycle(s)) with the longest dosing cycle having exceeded 1 year.

15 patients (46.9%) had an ECOG PS of 0 and 17 patients (53.1%) had an ECOG PS of 1. There were 9 patients (28.1%) with HER2 IHC 1+, 16 patients (50.0%) with IHC 2+, and 7 patients (21.9%) with IHC 3+. Among all the patients, 46.9% are BC patients, including 10 patients with HER2-low expressing BC and 5 patients with HER2-high expressing BC, 15.6% are patients with ovarian cancer, and 12.5% are patients with bladder cancer, involving 8 different tumor types. Efficacy: As of October 26, 2023, with a median follow-up of 4.2 months (95% CI: 2.3 to 5.8), 20 patients (62.5%) are still on treatment, PFS and DoR are not yet mature, and the ORR is subject to further observation.

Among the 30 patients who have undergone at least one tumor evaluation, the ORR was 46.7% (95% CI: 28.3% to 65.7%) and the DCR was 90.0% (95% CI: 73.5% to 97.7%). The ORR was 40.0% (95% CI: 12.2% to 73.8%) in patients with HER2-low xpression BC and 75.0% (95% CI: 19.4% to 99.4%) in patients with HER2-high expressing BC. Safety: Among the 32 enrolled patients, TRAEs at grade 3 or higher levels occurred in 2 patients (6.3%) and drug-related hematologic toxicity occurred in 1 patient without interstitial lung disease (ILD).

No patients experienced drug-related serious adverse events. The dose was escalated to a dose of 8.4 mg/kg, without the occurrence of dose-limiting toxicities, and the trial did not reach the maximum tolerated dose (the "MTD"). Conclusions: JSKN003 has shown initial efficacy in HER2-expressing solid tumors, and has been well tolerated by the treated patients, without dose-limiting toxicity or reaching the MTD.

A phase I/II clinical trial of JSKN003 is currently undergoing in China, with 56 subjects enrolled as of October 26, 2023, the safety profile of which was consistent with that of JSKN003-101, and no additional safety signal was identified.