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A novel antibody-drug conjugate called izalontamab brengitecan (iza-bren) doubled progression-free survival compared to chemotherapy in heavily pretreated HR-positive, HER2-negative breast cancer patients, a randomized Chinese trial showed. Median PFS jumped from 4 months with chemo to 8.2 months with iza-bren, with a disease control rate of 86.3% vs. 63.7%. The benefits came with significantly higher toxicity, though discontinuation rates were similar between groups.
A first-in-class antibody-drug conjugate (ADC), izalontamab brengitecan (iza-bren), has shown striking efficacy in patients with heavily pretreated hormone receptor (HR)-positive, HER2-negative breast cancer — a population with historically poor outcomes. The PANKU-Breast01 trial, conducted across 72 centers in China and published simultaneously in The Lancet, found that iza-bren more than doubled median progression-free survival (PFS) compared to chemotherapy. The advantage held across all prespecified subgroups, and twice as many patients responded to iza-bren. This builds on earlier wins for the drug in triple-negative breast cancer and advanced bladder cancer, and it has also received FDA breakthrough therapy designation for non-small cell lung cancer.
The results were presented at the European Society for Medical Oncology (ESMO) congress in Madrid. Experts noted that while the efficacy is impressive, the comparison was against chemotherapy — not another ADC like trastuzumab deruxtecan — leaving iza-bren's relative standing in the ADC landscape unclear. Questions also remain about cross-resistance with other topoisomerase-1 payload drugs and safety in older patients.
By the Numbers:
Why it matters: HR-positive breast cancer inevitably develops resistance to standard therapies, leaving patients with few good options. Iza-bren's significant PFS improvement positions it as a potential new standard of care in this setting — though its toxicity profile and place in ADC sequencing will need further study.
