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Targeted drug shrinks tumors in 3 out of 4 patients with advanced breast cancer
A phase three trial found that trastuzumab rezetecan delayed tumour growth more than standard chemotherapy in women with advanced breast cancer whose tumours have low levels of HER2. The findings suggest the drug could offer patients longer before their cancer worsens, including across hormone receptor-positive and hormone receptor-negative disease.
The study randomly assigned 551 women at 73 hospitals in China to receive the drug every three weeks or a doctor’s choice of chemotherapy, between June 2023 and August 2025. Median time before the cancer progressed was 16.4 months with the drug and 6.8 months with chemotherapy; tumours shrank in 75.5% and 41.2% of patients respectively. Serious side effects were reported in more than 84% of those given the drug, against nearly 68% receiving chemotherapy, and researchers said further study is needed.
In short
- The drug extended median time without progression to 16.4 months.
- Tumours shrank in 75.5% of patients treated with it.
- Serious side effects were more common than with chemotherapy.
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The case for
The trial suggests trastuzumab rezetecan may give women with advanced, HER2-low breast cancer substantially longer before their disease progresses, with tumours shrinking more often than on the chemotherapy used for comparison. If further research confirms these results, the added time and potential benefit across hormone receptor groups could make it a valuable option for patients with limited choices.
The case against
The apparent benefit needs to be weighed against the high rate of serious side effects, which was greater with the drug than with chemotherapy. The trial involved patients treated at hospitals in China, and researchers say more study is needed, so the results may not yet establish how the drug’s benefits and risks compare across broader patient groups or in routine care.
Explained simply
Breast cancer can spread from the breast to other parts of the body, where it is described as advanced. Doctors classify tumours partly by whether they have certain receptors, including HER2, a protein that can help cancer cells grow; “HER2-low” means the cells have some of the protein, but not much.
Trastuzumab rezetecan is a targeted medicine designed to deliver cancer treatment to cells with HER2. It is being studied in women whose advanced cancer has low HER2 levels, including cancers that differ in their hormone receptors, which can also affect how doctors choose treatment.
The trial compared the medicine with chemotherapy, a treatment that acts on cancer cells but can also affect healthy cells. Its results matter because treatment options can be limited once breast cancer has spread, while side effects and how long a treatment holds the disease in check are important considerations.
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