Suzhou, China, June 2, 2026 - Alphamab Oncology (stock code: 9966.HK) today announced that the results from a Phase I clinical study (JSKN016-101, NCT06592417) of its first-in-class TROP2/HER3 bispecific antibody-drug conjugate (ADC) JSKN016, for the treatment of HER2-negative locally advanced or metastatic breast cancer (BC), were presented as a poster at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting.

Title: JSKN016, a First-in-Class Anti-TROP2/HER3 Bispecific Antibody-Drug Conjugate (ADC) in Patients (pts) with HER2-Negative Locally Advanced or Metastatic Breast Cancer: Results from a Phase I Study

Abstract Number: 1123

Principal Investigator: Professor Herui Yao, Sun Yat-sen Memorial Hospital, Sun Yat-sen University

Presentation Time: June 1, 2026, 1:30-4:30 PM CDT

TROP2 and HER3 are frequently overexpressed in HER2-negative BC and are associated with poor prognosis and treatment resistance. JSKN016 is a TROP2/HER3 targeting bispecific ADC developed using the proprietary single-domain antibody and bispecific antibody platforms. It is conjugated via site-specific glycosylation to generate a homogeneous and stable ADC with a drug-to-antibody ratio (DAR) of 4. JSKN016 precisely binds to TROP2 and/or HER3 on tumor cells, blocks tumor signaling pathways, and releases topoisomerase I inhibitors for precise and potent antitumor activity. The glycan conjugation technology confers high stability and low off-target toxicity. The 2026 ASCO Annual Meeting features the presentation of analytical results from the HER2-negative BC cohort of the Phase I clinical study of JSKN016 in China.

Study Design

JSKN016-101 (NCT06592417) is an open-label, multicenter Phase I study in patients with advanced malignant solid tumors in China, consisting of dose-escalation and dose-expansion phases. The study aims to evaluate the safety, tolerability, pharmacokinetics/pharmacodynamics, and antitumor activity of JSKN016, and to determine the maximum tolerated dose (MTD) and/or recommended Phase II dose (RP2D). In the dose escalation stage, six dose levels of 0.5, 1, 2, 4, 6 and 8mg/kg were explored, with JSKN016 administered once every three weeks (Q3W), The MTD was not reached at any of the explored dose levels, and the RP2D for patients with BC was established at 6mg/kg Q3W.

Study Results

As of December 22, 2025, a total of 82 patients with HER2- negative BC, including 50 patients with triple-negative breast cancer (TNBC) and 32 patients with HR+/HER2- BC, were enrolled and received JSKN016 across three dose levels, with 14 patients at the dose of 4mg/kg, 65 patients at the dose of 6mg/kg (being the RP2D), and 3 patients at the dose of 8mg/kg.

Among all enrolled patients, 98.8% (81 patients) of them had stage IV BC and 7.3% (6 patients) of them had brain metastases. The baseline characteristics were generally balanced between the two subgroups. The median age was 50 years old in the TNBC subgroup and 52 years old in the HR+/HER2- BC subgroup, with 78% and 75% of them having ECOG PS 1, respectively. All patients with TNBC had received prior taxane-based chemotherapy, and all patients with HR+/HER2- BC had experienced disease progression after at least one line of endocrine therapy in combination with a CDK4/6 inhibitor and at least one line of chemotherapy.

The data showed that JSKN016 demonstrated robust and durable efficacy in later-line treatment of HER2-negative BC. With longer follow-up and further data maturation, efficacy is expected to improve:

• TNBC subgroup (RP2D): In 31 evaluable patients, investigator-assessed objective response rate (ORR) was 64.5%, and median progression-free survival (mPFS) was 7.6 months; independent review committee (IRC)-assessed ORR was 61.3% and mPFS was 7.9 months.
• HR+/HER2- BC subgroup (RP2D): In 29 evaluable patients, investigator-assessed ORR was 51.7%, mPFS was not yet mature; IRC-assessed ORR was 55.2% and mPFS was 11.1 months, with a 6-month PFS rate of 84.5%.

With the data cutoff date extended to March 17, 2026, efficacy data at the RP2D further improved:

• TNBC subgroup: Investigator-assessed ORR remained 64.5%, disease control rate (DCR) reached 83.9%, and mPFS was 8.5 months (95% CI: 4.11–10.02).
• HR+/HER2- BC subgroup: Investigator-assessed ORR remained 51.7%, DCR reached 100%. mPFS was not yet mature, and the 12-month PFS rate was 61.7%.

As of March 17, 2026, with a median follow-up of 7.8 months, JSKN016 demonstrated a promising safety profile. At the RP2D:

• Treatment-related adverse events (TRAEs) at grade 3 or above were reported in 24.6% of patients, with no grade 4 or 5 TRAEs reported.
• Serious adverse events (SAEs) were reported in 15.4% of patients, of which 12.3% were treatment-related.
• Dose reduction due to TRAEs occurred in 46.2% of patients. Only 1 patient (1.5%) permanently discontinued treatment due to grade 3 conjunctivitis. No TRAEs led to death.
• No interstitial lung disease (ILD) was observed during the study.
• The most common grade 3 TRAEs were neutrophil count decreased (7.7%), white blood cell count decreased (6.2%), amylase (4.6%), stomatitis (4.6%), asthenia (1.5%), lymphocyte count decrease (1.5%), weight decrease (1.5%), abdominal pain (1.5%), anemia (1.5%) and conjunctivitis (1.5%).

Conclusions

JSKN016 demonstrated very promising efficacy and superior safety profile in late line HER2-negative BC patients. The dual-targeting mechanism brings enhanced efficacy while leveraging the glycan-conjugation technology minimizes adverse reactions, offering a distinct safety advantage.

The results guarantee the further development of JSKN016, in combination with chemotherapy, immunotherapy and other targeted therapies, in front line and perioperative settings. Currently, multiple Phase II studies of JSKN016 as monotherapy and in combination for lung cancer, breast cancer, and other indications are ongoing, and a Phase III study for TNBC is underway. JSKN016 is expected to bring more effective and safer treatment options to patients.

About JSKN016

JSKN016 is a TROP2/HER3 targeting bispecific ADC developed using the proprietary single-domain antibody and bispecific antibody platforms. It is conjugated via site-specific glycosylation to generate a homogeneous and stable ADC with a drug-to-antibody ratio (DAR) of 4. JSKN016 binds to TROP2 and/or HER3 on tumor cells, blocks the corresponding signaling pathways and releases topoisomerase I inhibitors through cellular endocytosis, exerting anti-tumor effects.

JSKN016 has demonstrated superior efficacy and a favorable safety profile across multiple solid tumors. Multiple clinical studies of JSKN016 as monotherapy and in combination therapies for lung cancer, breast cancer, and other indications have been initiated. The Phase III clinical study evaluating JSKN016 for the treatment of triple-negative breast cancer (TNBC) is currently ongoing. The investigational new drug (IND) application for a Phase Ib study in China of the subcutaneous formulation of JSKN016 has been approved by the CDE, and the Phase I clinical study in Australia is ongoing.

About Alphamab Oncology

Alphamab Oncology (Stock Code: 9966.HK) is an innovative biopharmaceutical company focused on oncology. Leveraging proprietary platforms-including single-domain antibodies, bispecific antibodies, glycan-specific conjugation, linker-payloads, dual-payload ADCs, and high-concentration subcutaneous formulations, the Company has built a differentiated and globally competitive pipeline, covering cutting-edge candidates in ADCs, bispecific antibodies, and single-domain antibodies.

Two products have received market approval: Envafolimab (KN035, brand name: 恩维达^®), the world's first subcutaneously injected PD-(L)1 inhibitor, offering greater convenience and accessibility in cancer treatment; and Anbenitamab (KN026, brand name: 恩尼妥^®), the first domestically developed HER2 bispecific antibody approved for marketing in China, redefining the standard of treatment for second‑line HER2‑positive gastric cancer. Six bispecific ADC, dual-payload ADC candidates have entered clinical stages, and next-generation ADC pipelines are advancing rapidly. The Company has established strategic partnerships with organizations including CSPC, ArriVent, and Glenmark, covering both product development and technology platforms.

Our overarching mission is to make cancer manageable and curable by addressing unmet clinical needs in oncology. Alphamab Oncology is continuously dedicated to the development of effective, safe, and globally competitive anti-tumor drugs, enabling patients to achieve long-term, high-quality survival and delivering China-innovated cancer therapies to benefit patients worldwide.

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