Izalontamab Brengitecan Meets Dual Survival Endpoints in Phase 3 TNBC and Esophageal Cancer Trials

SystImmune, via its parent company Sichuan Biokin Pharmaceutical (Biokin), and Bristol Myers Squibb announced that prespecified interim analyses of 2 phase 3 trials evaluating izalontamab brengitecan (iza-bren), an investigational epidermal growth factor receptor and human epidermal growth factor receptor 3 (EGFRxHER3) bispecific antibody-drug conjugate (ADC), met dual primary endpoints of overall survival (OS) and progression-free survival (PFS). The results were shown in both unresectable locally advanced or metastatic triple-negative breast cancer (TNBC) and recurrent or metastatic esophageal squamous cell carcinoma (ESCC).¹

These results mark the first phase 3 bispecific ADC to report positive dual primary endpoint data in either tumor type and extend iza-bren's positive phase 3 record to three distinct cancer indications following earlier results in nasopharyngeal carcinoma, according to the companies.¹

"Iza-bren can address a critical gap for patients who develop resistance or experience disease progression after prior therapies and may also hold potential in earlier lines of therapy," said Cristian Massacesi, MD, executive vice president, chief medical officer, and head of development at Bristol Myers Squibb, in a company press release.¹

What did the PANKU-Breast02 interim analysis show in pretreated metastatic TNBC?

The PANKU-Breast02 (BL-B01D1-307) trial enrolled patients with unresectable locally advanced or metastatic TNBC whose disease had progressed following one to two prior lines of systemic therapy for advanced disease, including prior taxane therapy. Patients were randomized 1:1 to iza-bren (n=207) or physician's choice of chemotherapy (n=211), comprising eribulin, capecitabine, gemcitabine, or vinorelbine. At a median follow-up of 11 months, median OS was 15.9 months with iza-bren versus 12.5 months with chemotherapy (HR: 0.60; 95% CI: 0.42–0.85; p=0.0019). Median PFS by blinded independent central review (BICR) was 8.5 months versus 3.1 months (HR: 0.29; 95% CI: 0.22–0.38; p<0.0001).

Confirmed objective response rate by BICR was 51.7% with iza-bren compared to 20.5% with chemotherapy (odds ratio, 4.3; 95% CI: 2.8–6.7). Grade >3 treatment-emergent adverse events were predominantly hematologic. Interstitial lung disease (ILD) of any grade was reported in 1.4% of iza-bren–treated patients (one grade 1, two grade 2 events), with treatment discontinuation due to adverse events in 1.9%.

What did the PANKU-Esophagus01 interim analysis show in previously treated recurrent or metastatic ESCC?

The PANKU-Esophagus01 (BL-B01D1-305) trial enrolled patients with recurrent or metastatic ESCC who had progressed after first-line programmed cell death protein 1/programmed cell death ligand 1 inhibitor plus platinum-based chemotherapy, randomized to iza-bren (n=249) or physician's choice chemotherapy (n=248). Median OS was 9.8 months with iza-bren versus 7.2 months with chemotherapy (HR: 0.64; 95% CI: 0.49–0.83; p=0.0004). Median PFS by BICR was 4.2 months versus 2.0 months (HR: 0.50; 95% CI: 0.40–0.63; p<0.0001). ORR by BICR was 35.3% with iza-bren versus 13.1% with chemotherapy.

Grade >3 treatment-related adverse events (TRAEs) occurred in 85.1% of iza-bren patients, predominantly hematologic in nature, compared to 60.2% in the chemotherapy arm. ILD rates were low in both arms (all grades showed 1.6% iza-bren vs. 0.4% chemotherapy). Treatment-related deaths occurred in 1.2% and 1.6% of patients, respectively. A new drug application for the ESCC indication has been accepted by China's National Medical Products Administration (NMPA) under priority review, according to the companies.¹

What is the clinical context and unmet need in pretreated TNBC and metastatic ESCC?

TNBC accounts for approximately 15% to 20% of all breast cancers and is characterized by the absence of estrogen receptor, progesterone receptor, and HER2 expression, limiting targeted treatment options.² In the metastatic setting following prior systemic therapy, median OS with standard chemotherapy has historically ranged from approximately 12 to 13 months, and durable responses are uncommon.²

ESCC represents the predominant histologic subtype of esophageal cancer in Asia and carries a 5-year survival rate below 5% in the metastatic setting. Outcomes following progression on first-line immunotherapy-containing regimens remain poor, with no established standard of care.^3,4 Both indications represent areas of significant unmet need in which incremental survival improvements carry meaningful clinical weight.

What limitations apply to these interim analyses, and what additional data are needed?

Both datasets are interim analyses with follow-up periods of approximately 11 months or less, and OS data remain preliminary. The trials were conducted in mainland China under Biokin sponsorship, which may raise questions about generalizability to Western patient populations who may have potentially different prior treatment histories, disease biology, and supportive care standards. The high rate of grade >3 TRAEs in the ESCC cohort (85.1%) suggest that careful evaluation is needed in the context of benefit–risk assessment, particularly given the heavily pretreated population. Regulatory submissions outside China have not yet been announced, and the timeline for potential US or European filings based on these data have not been disclosed at this time.

References

1. Bristol Myers Squibb. Izalontamab brengitecan (Iza-Bren) demonstrates statistically significant and clinically meaningful improvements in overall survival and progression-free survival in patients with triple-negative breast cancer and esophageal squamous cell carcinoma. Published June 2, 2026. Accessed June 2, 2026. https://news.bms.com/news/details/2026/Izalontamab-Brengitecan-Iza-Bren-Demonstrates-Statistically-Significant-and-Clinically-Meaningful-Improvements-in-Overall-Survival-and-Progression-Free-Survival-in-Patients-with-Triple-Negative-Breast-Cancer-and-Esophageal-Squamous-Cell-Carcinoma/default.aspx
2. Cortes J, Cescon DW, Rugo HS, et al. Pembrolizumab plus chemotherapy versus placebo plus chemotherapy for previously untreated locally recurrent inoperable or metastatic triple-negative breast cancer (KEYNOTE-355): a randomised, placebo-controlled, double-blind, phase 3 clinical trial. Lancet. 2020;396(10265):1817-1828. doi:10.1016/S0140-6736(20)32531-9
3. Fang P, Zhou J, Liang Z, et al. Immunotherapy resistance in esophageal cancer: Possible mechanisms and clinical implications. Front. Immunol. 2022;13:975986. doi:10.3389/fimmu.2022.975986
4. Chen Y, Chen Z, Guo H, et al. Clinical benefits of combination immunotherapy over standard immunotherapy monotherapy in previously treated advanced esophageal squamous cell carcinoma: A systematic review and meta-analysis. Cancer Med. 2025;14(21):e71329. doi:10.1002/cam4.71329