SystImmune and Bristol Myers Squibb announce encouraging interim Phase III data for izalontamab brengitecan (Iza-bren) in previously treated metastatic triple-negative breast cancer (TNBC), highlighting potential improvements in patient outcomes.
SystImmune, Inc. and Bristol Myers Squibb have announced positive topline results from a pre-specified interim analysis of a pivotal Phase III clinical trial evaluating izalontamab brengitecan (iza-bren), an investigational EGFR×HER3 bispecific antibody-drug conjugate (ADC), in patients with previously treated, unresectable locally advanced or metastatic triple-negative breast cancer (TNBC). The results mark a significant milestone for the program and further reinforce the growing promise of next-generation bispecific ADCs in hard-to-treat cancers.
The findings were reported by SystImmune’s parent company, Sichuan Biokin Pharmaceutical Co., Ltd. (Biokin), which is sponsoring the Phase III BL-B01D1-307 study in Mainland China. Outside of China, iza-bren is being jointly developed by SystImmune and Bristol Myers Squibb under a global collaboration and exclusive license agreement.
Strong Survival Benefit in Phase III TNBC Study
The Phase III BL-B01D1-307 trial is evaluating iza-bren in patients with unresectable locally advanced or metastatic TNBC whose disease had progressed following prior taxane-based therapy. Triple-negative breast cancer is one of the most aggressive and challenging subtypes of breast cancer, characterized by the absence of estrogen receptor (ER), progesterone receptor (PR), and HER2 expression. As a result, treatment options are more limited compared to other breast cancer subtypes, and patients often face poor prognoses once standard therapies fail.
According to the interim analysis, iza-bren demonstrated statistically significant and clinically meaningful improvements in both progression-free survival (PFS) and overall survival (OS) compared to chemotherapy of physician’s choice. The study successfully met both dual primary endpoints, a notable achievement in a patient population with substantial unmet medical need.
Progression-free survival measures the length of time during and after treatment that a patient lives without disease progression, while overall survival remains the gold standard endpoint in oncology, reflecting the length of time patients survive after treatment initiation. Achieving significant improvement in both endpoints underscores the potential of iza-bren to deliver meaningful clinical benefit beyond current treatment options.
Importantly, this marks the third Phase III trial in which iza-bren has achieved its primary endpoint or endpoints. It is also the first bispecific ADC in a Phase III study to report dual positive PFS and OS results in triple-negative breast cancer, setting a potential new benchmark in the field.
Addressing an Urgent Unmet Need
Patients with advanced TNBC who progress after standard chemotherapy face limited therapeutic options and typically experience rapid disease progression. In this setting, treatment goals focus not only on extending survival but also on maintaining quality of life and controlling symptoms.
Dr. Yi Zhu, Chief Executive Officer of Biokin, emphasized the significance of the results, noting that patients with advanced TNBC urgently require more effective therapies once frontline options have failed. He stated that the topline findings further strengthen confidence in iza-bren’s potential to deliver meaningful clinical benefit across multiple tumor types.
From the perspective of global development, Bristol Myers Squibb also highlighted the broader implications of the data. Cristian Massacesi, Executive Vice President, Chief Medical Officer and Head of Development at Bristol Myers Squibb, remarked that the results underscore the transformative potential of bispecific ADC technology targeting both EGFR and HER3. He emphasized the company’s commitment to advancing ADC science in pursuit of new treatment options for people living with difficult-to-treat cancers.
A Novel Bispecific ADC Approach
Izalontamab brengitecan represents a new generation of antibody-drug conjugates. Traditional ADCs consist of a monoclonal antibody linked to a cytotoxic payload, enabling targeted delivery of chemotherapy directly to cancer cells expressing a specific antigen. Bispecific ADCs take this concept further by targeting two distinct antigens simultaneously.
Iza-bren is designed to bind both EGFR (epidermal growth factor receptor) and HER3 (human epidermal growth factor receptor 3), two receptors frequently implicated in tumor growth, survival, and resistance mechanisms across multiple solid tumors. By targeting both pathways, the therapy aims to enhance tumor selectivity, overcome resistance, and improve antitumor activity compared to single-target approaches.
The dual-target strategy may be particularly relevant in TNBC, where heterogeneity and pathway cross-talk contribute to therapeutic resistance. The positive PFS and OS outcomes suggest that simultaneous targeting of EGFR and HER3 could represent a powerful strategy for improving outcomes in aggressive breast cancers.
Expanding Regulatory Momentum
Beyond the TNBC indication, iza-bren has been gaining regulatory traction across several tumor types.
In China, the National Medical Products Administration’s Center for Drug Evaluation (CDE) has granted Breakthrough Therapy Designation (BTD) to iza-bren for seven indications, highlighting the therapy’s potential to address serious conditions with significant unmet need. Additionally, two New Drug Applications (NDAs) for iza-bren have been accepted by the CDE and included in the priority review process. These applications cover:
- Locally advanced or metastatic nasopharyngeal carcinoma
- Recurrent or metastatic esophageal squamous cell carcinoma
In the United States, the U.S. Food and Drug Administration has also granted Breakthrough Therapy Designation to iza-bren for previously treated non-small cell lung cancer (NSCLC) patients harboring an EGFR mutation. Breakthrough Therapy Designation is intended to expedite the development and review of drugs that show substantial improvement over existing therapies for serious or life-threatening diseases.
The growing number of designations and regulatory filings reflects a broad development strategy aimed at positioning iza-bren as a potential multi-indication oncology therapy.
Global Development Collaboration
The collaboration between SystImmune and Bristol Myers Squibb combines regional clinical development strength in China with global oncology expertise. Biokin sponsors and leads the BL-B01D1-307 trial in Mainland China, while SystImmune and Bristol Myers Squibb are responsible for joint development efforts outside of China under their exclusive licensing agreement.
This partnership structure enables coordinated global development while leveraging local regulatory and clinical capabilities, potentially accelerating access to patients worldwide if approved.
