A HER2-targeted drug held off HER2-low breast cancer far longer than chemotherapy
Breast, ovarian and uterine cancerPart of a story we are following · 8 articles · See every update
Women with HER2-low metastatic breast cancer went a median 16.4 months without progression on trastuzumab rezetecan vs. 6.8 months on chemotherapy, with more serious blood-related side effects, in a phase 3 trial in China published Oct. 23, 2026, in JAMA. It is a new option for one of the most common women’s cancers.
For years, breast cancers were classed simply as HER2-positive or HER2-negative. Then doctors realized that many “negative” tumors have small amounts of HER2, now called HER2-low (or ERBB2-low), and that antibody-drug conjugates can target them.
Women on trastuzumab rezetecan went a median of 16.4 months before their cancer grew, compared with 6.8 months on chemotherapy.
What is trastuzumab rezetecan?
It’s an antibody-drug conjugate: the antibody trastuzumab finds HER2 on cancer cells and carries a chemotherapy payload directly to them.
What did the trial test?
At 73 hospitals in China, 551 women with HER2-low metastatic breast cancer who had received at most one prior chemotherapy for metastatic disease were assigned by chance to trastuzumab rezetecan, given by IV every 3 weeks, or the doctor’s choice of chemotherapy. Reviewers who didn’t know the treatment judged progression.
What did the study find about women’s cancers?
| Trastuzumab rezetecan | Chemotherapy | |
|---|---|---|
| Median time without progression, overall | 16.4 months | 6.8 months |
| Median time without progression, no prior chemo | 16.6 months | 6.8 months |
| Grade 3+ treatment side effects | 84.1% | 67.9% |
| Low neutrophil counts | 65.2% | 54.2% |
The hazard ratio was 0.27 overall. The benefit was seen both in hormone receptor-positive and hormone receptor-negative tumors.
Why does this matter?
HER2-low tumors are common, and these women used to have no HER2-targeted options. A large gain in time without progression, early in the course of metastatic disease, gives them a strong new choice.
How solid is this evidence?
It’s strong for what it measured. Mongevity rates it A on our A-to-E scale: a large randomized phase 3 trial with blinded review. Limits: it was open-label, done only in China, survival data aren’t reported yet and serious side effects, mostly low white blood cells, were frequent.
What does this mean for you?
If you or someone close to you has metastatic breast cancer considered HER2-negative, ask whether the tumor was tested for HER2-low status. It may open the door to antibody-drug conjugates. Ask, too, how blood counts would be monitored.
How do I explain this at dinner?
Some breast cancers have just a little bit of a target called HER2. A new medicine finds even that little bit and delivers chemo right to the cancer, keeping it in check much longer than standard chemo. A good question for the table: why might a small target still be worth aiming at?
In one sentence: trastuzumab rezetecan kept HER2-low metastatic breast cancer from growing far longer than chemotherapy did, with more serious blood-related side effects.
Questions and answers
- What is HER2-low breast cancer?
- Breast cancer with small amounts of HER2 that was previously classed as HER2-negative.
- How well did trastuzumab rezetecan work?
- Median time without progression was 16.4 months vs. 6.8 months with chemotherapy.
- Is it harder to tolerate?
- Serious side effects were more frequent (84.1% vs. 67.9%), mostly low neutrophil counts.
