Bristol Myers Squibb reports positive Phase 3 results for breast cancer drug
Key Facts
Bristol Myers Squibb and SystImmune announced positive results from the Phase 3 PANKU-Breast01 trial of izalontamab brengitecan, known as iza-bren. The study tested efficacy and safety in patients with hormone receptor-positive, HER2-negative breast cancer after prior treatment. The results concern an investigational drug, while overall survival data were immature at the time of analysis.
The open-label, randomized trial compared iza-bren with chemotherapy at 72 hospitals in China. The study population included patients whose disease had progressed after hormonal therapy, CDK 4/6 inhibitors and one or two lines of chemotherapy. Participants had hormone receptor-positive, HER2-negative breast cancer, consistent with the population the trial was designed to assess. The study aimed to compare the drug's efficacy and safety with chemotherapy in previously treated patients. This design places the findings in the context of patients who had already received hormonal and chemotherapy treatments, rather than patients starting treatment.
Between April 24, 2024, and June 6, 2025, 560 patients were screened, and 177 were excluded. A total of 383 patients were then randomly assigned and treated in two groups; 190 received iza-bren, while 193 received chemotherapy. An analysis of progression-free survival showed a statistically significant advantage for the drug compared with chemotherapy, with a p-value of less than 0.0001. This measure tracks the period during which the disease does not progress, while overall survival remained immature at the time of analysis.
The improvement in progression-free survival was accompanied by an increase in treatment-related adverse events of Grade 3 or higher. These events were reported in 85% of patients in the iza-bren group, compared with 66% in the chemotherapy group, according to the study summary published in The Lancet. Hematologic events were the most common in both groups. These figures present the safety side of the comparison alongside the efficacy result, which showed improvement in favor of the drug. Reading the trial results therefore involves weighing the efficacy measure against the higher rate of severe treatment-related adverse events in the investigational group.
Overall survival remained immature in the interim analysis, and the drug had not demonstrated a benefit on this measure at that time, according to the study summary. The researchers said the results could make iza-bren a potential treatment option for this population in China, while evaluation in global populations and earlier lines of treatment for HER2-negative breast cancer is needed. The study was registered as NCT06343948, and enrollment has closed. The study is sponsored by Biokin in China, while Bristol Myers Squibb and SystImmune are developing the drug outside China. The current results are specific to a clinical trial of an investigational drug and do not, on their own, establish approval or make it a standard of care.