Shanghai, China, May 13, 2026 — Shanghai Henlius Biotech, Inc. (2696.HK) announced that the first patient has been dosed in a Phase 1 clinical trial of HLX97, a novel oral lysine acetyltransferase 6A/B (KAT6A/B) small molecule inhibitor, in patients with advanced or metastatic solid tumors in China. Previously, the Investigational New Drug (IND) application for HLX97 in advanced/metastatic solid tumors was approved by the China National Medical Products Administration (NMPA).

Breast cancer is the second most common cancer worldwide and the most common malignant tumor among women, and it is also a leading cause of cancer-related death in women. ER-positive (ER+) breast cancer is the most prevalent subtype, accounting for approximately 70% of all cases.¹ While endocrine therapies—such as estrogen suppression and direct targeting of the estrogen receptor—have become the cornerstone of treatment and significantly reduced recurrence and mortality, both primary and acquired resistance remain major clinical challenges.

KAT6A (Lysine Acetyltransferase 6A) and its paralog KAT6B (Lysine Acetyltransferase 6B) are members of the MYST family of histone acetyltransferases (HATs) and play key roles in tumorigenesis, disease progression, and the development of drug resistance across multiple cancer types. Preclinical and clinical studies have shown that amplification and/or overexpression of the KAT6A gene is closely associated with endocrine resistance in heavily pretreated patients with ER+/HER2- metastatic breast cancer. In addition, aberrant expression of KAT6A/B has been observed in a range of solid tumors, including ovarian, cervical, colorectal, prostate, lung cancers, and gliomas, suggesting broad therapeutic potential for KAT6A/B inhibitors across tumor types.^2-4 Given that amplification and/or overexpression of the KAT6A gene in breast cancer has been shown to be closely associated with the development of endocrine resistance, targeting KAT6A/B activity may represent a promising strategy to overcome endocrine therapy resistance in breast cancer.^5-6

HLX97 is a novel oral KAT6A/B inhibitor with best-in-class potential. By selectively inhibiting KAT6A/B activity, HLX97 is designed to regulate tumor cell proliferation and induce apoptosis. It demonstrates high selectivity and favorable pharmacokinetic properties characterized by rapid onset and clearance, aiming to maximize antitumor activity while minimizing hematological toxicity. Preclinical studies have shown that HLX97 effectively inhibits KAT6A/B activity and exhibits strong antitumor efficacy with a favorable safety profile. In animal models, HLX97 demonstrated significant efficacy in ER-positive breast cancer as well as in human-derived xenograft models resistant to both fulvestrant and palbociclib (a CDK4/6 inhibitor), with good overall tolerability.

Henlius has built a comprehensive pipeline covering the full continuum of breast cancer care through internal innovation and strategic collaborations. Its marketed products include HANQUYOU (trade name: HERCESSI^™ in the U.S., Zercepac^® in Europe), a trastuzumab biosimilar approved in over 50 countries and regions including China, the U.S., and Europe; POHERDY^®, the first pertuzumab biosimilar approved in the U.S.; HANNAIJIA (neratinib), an extended adjuvant therapy for early-stage breast cancer, and CDK4/6 inhibitor FUTUONING (fovinaciclib). Meanwhile, Henlius is advancing next-generation molecules such as novel epitope anti-HER2 antibody HLX22, oral selective estrogen receptor modulator (SERM) lasofoxifene (HLX78), KAT6A/B inhibitor HLX97, LIV-1-targeting ADC HLX41, HER2×HER2 bispecific epitope ADC HLX49 and HER2 ADC HLX87 through its robust innovation platforms and collaborative R&D. Building on this foundation, Henlius remains committed to advancing monotherapies and combination regimens across all breast cancer subtypes, enhancing therapeutic value through strengthened pipeline synergies.

Moving forward, Henlius will continue to focus on unmet clinical needs by fully leveraging its integrated platform advantages in antibody-based drugs, expanding disease areas, accelerating the development of differentiated molecules, and bringing more high-quality, affordable innovative therapies to patients worldwide.

About HLX97-FIH101

This study is a multicenter, open-label phase 1 clinical trial designed to evaluate the safety, tolerability, pharmacokinetic (“PK”) characteristics, and preliminary antitumor activity of HLX97 in patients with advanced or metastatic solid tumors. The study consists of two parts: Part 1 is the dose‑escalation phase, which includes monotherapy dose escalation (Part 1A) and combination therapy dose escalation (Part 1B); Part 2 is the dose‑expansion phase. Part 1A, the monotherapy dose‑escalation phase, will be conducted in patients with advanced/metastatic solid tumors and will include five dose levels ranging from 1.0 mg to 15.0 mg. HLX97 will be administered orally from Day1 to Day28 of each cycle, once a day, for 4 weeks each cycle. Part 1B, the combination therapy dose‑escalation phase, will explore 2 to 3 dose levels of HLX97 in combination with fulvestrant in patients with HR‑positive, HER2‑negative locally advanced or metastatic breast cancer. Part 2 will be conducted in patients with HR‑positive, HER2‑negative locally advanced or metastatic breast cancer and will include 3 treatment groups: two groups receiving different doses of HLX97 in combination with fulvestrant, and one group receiving fulvestrant monotherapy. The primary endpoints of Part 1 are to evaluate the incidence of dose‑limiting toxicities (DLT) and to determine the maximum tolerated dose (MTD) of HLX97 as monotherapy and in combination with fulvestrant. The primary endpoints of Part 2 are the objective response rate (ORR) and progression‑free survival (PFS) as assessed by the investigator according to RECIST version 1.1, as well as the recommended Phase 2 dose (RP2D) of HLX97 in combination with fulvestrant. Secondary endpoints include the safety of HLX97 as monotherapy and in combination, PK parameters, additional efficacy endpoints (such as duration of response (DOR), disease control rate (DCR), and overall survival (OS)), and exploratory pharmacodynamic and predictive biomarker analyses.