SystImmune and Bristol Myers Squibb Report Positive Phase III Results for Izalontamab Brengitecan in Triple-Negative Breast Cancer

Bispecific ADC demonstrates statistically significant and clinically meaningful improvement in progression-free and overall survival

Published on Feb. 26, 2026

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SystImmune, Inc. and Bristol Myers Squibb announced positive topline results from a Phase III study evaluating izalontamab brengitecan (iza-bren), an EGFR×HER3 bispecific antibody-drug conjugate, in patients with unresectable locally advanced or metastatic triple-negative breast cancer whose disease progressed following prior taxane therapy. The study met its dual primary endpoints of progression-free survival and overall survival, showing statistically significant and clinically meaningful improvement compared to chemotherapy of physician's choice.

Why it matters

These results represent a significant milestone in the development of bispecific ADCs as a potential new treatment option for patients with advanced triple-negative breast cancer, a particularly aggressive and difficult-to-treat form of the disease. The positive data further strengthens confidence in iza-bren's potential to deliver meaningful clinical benefit across multiple cancer types.

The details

The Phase III study (BL-B01D1-307) is sponsored by SystImmune's parent company, Sichuan Biokin Pharmaceutical Co., Ltd., in Mainland China. Outside of China, iza-bren is jointly developed by SystImmune and Bristol Myers Squibb under a collaboration and exclusive license agreement. Iza-bren is a bispecific ADC that targets both EGFR and HER3, which are highly expressed in various epithelial cancers and associated with cancer cell proliferation and survival. The dual mechanism of action blocks EGFR and HER3 signals to cancer cells, reducing proliferation and survival, while the therapeutic payload causes cytotoxic stress leading to cancer cell death.

  • The pre-specified interim analysis of the Phase III study was conducted in February 2026.

The players

SystImmune, Inc.

A clinical-stage biopharmaceutical company located in Redmond, WA that specializes in developing innovative cancer treatments using bispecific, multi-specific antibodies, and antibody-drug conjugates.

Bristol Myers Squibb

A global biopharmaceutical company that is jointly developing iza-bren with SystImmune outside of China.

Sichuan Biokin Pharmaceutical Co., Ltd.

The parent company of SystImmune that is sponsoring the Phase III study of iza-bren in China.

Dr. Yi Zhu

Chief Executive Officer of Biokin.

Cristian Massacesi

Executive Vice President, Chief Medical Officer and Head of Development at Bristol Myers Squibb.

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What they’re saying

“Patients with advanced triple-negative breast cancer who progress after standard therapies face an urgent need for more effective options. These topline results further strengthen our confidence in iza-bren's potential to deliver meaningful clinical benefit across multiple cancers.”

— Dr. Yi Zhu, Chief Executive Officer of Biokin

“These results underscore the potential of bispecific ADC technology targeting both EGFR and HER3 to meaningfully change outcomes in difficult‑to‑treat cancers. We look forward to advancing the science and development of ADCs, with the hope of uncovering new options for people living with cancer.”

— Cristian Massacesi, Executive Vice President, Chief Medical Officer and Head of Development at Bristol Myers Squibb

What’s next

The data from this Phase III study will be presented at an upcoming medical meeting.

The takeaway

The positive results from this Phase III trial of iza-bren in triple-negative breast cancer represent a significant advancement in the development of bispecific ADCs as a potential new treatment option for patients with this aggressive and difficult-to-treat form of breast cancer.