Researchers are investigating a potential new treatment for advanced breast cancer. The focus is on the drug trastuzumab rezetecan, aimed at patients with ERBB2-low metastatic breast cancer. These patients’ tumors contain low levels of HER2, a protein that can facilitate cancer cell growth.
A phase 3 clinical trial called HORIZON-Breast06 is underway. This trial aims to determine if trastuzumab rezetecan is more effective than standard chemotherapy for this type of cancer.
Study Details
The trial involved 551 female patients across 73 hospitals in China. Participants were randomly assigned to receive either trastuzumab rezetecan intravenously every three weeks or a chemotherapy option chosen by their physician. Conducted from June 2023 to August 2025, the study revealed significant results.
The median period without tumor growth for those on trastuzumab rezetecan was 16.4 months, compared to 6.8 months for those receiving chemotherapy. This suggests the drug dramatically delays cancer progression.
Survival and Side Effects
Patients on trastuzumab rezetecan had a 73% lower chance of cancer worsening or death compared to chemotherapy recipients. Tumor reduction was observed in 75.5% of patients taking the drug, versus 41.2% with chemotherapy. After 12 months, 90.6% of trastuzumab rezetecan patients were alive compared to 81.4% of those on chemotherapy.
Despite promising survival benefits, side effects were more common, necessitating dose adjustments. Serious side effects affected over 84% of those on trastuzumab rezetecan, compared to nearly 68% on chemotherapy. Side effects included anemia and other blood-related issues.
Expert Opinions
The findings were published in JAMA. They indicate that trastuzumab rezetecan offers a significant progression-free survival advantage over chemotherapy for patients with ERBB2-low advanced breast cancer. Loren Rourke, a breast surgical oncologist, found the results “incredibly encouraging,” highlighting the importance of extended cancer control.
Rourke stressed that while the treatment delays progression, the quality of life must be considered due to side effects. More research is needed to comprehend these side effects, particularly blood count declines causing fatigue and infection risk.
Although pleased with the progress, experts like Rourke seek answers to critical questions. They emphasize the importance of understanding whether the treatment extends patients’ lives, not just delays cancer progression.
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