New drug holds HER2-low breast cancer back far longer, good news for women’s cancers

Here is good news among the women’s cancers. A new medicine kept advanced breast cancer from growing for far longer than standard chemotherapy did. It worked in a type called HER2-low, which is one of the most common kinds doctors see.

In the trial, women on the new drug, trastuzumab rezetecan, went about 16 months before their cancer grew. Women on chemotherapy went about 7 months. That is a real step forward for a group of patients who had few targeted choices.

How the study worked

Researchers at 73 hospitals in China enrolled 551 women with HER2-low breast cancer that had spread or come back and could not be removed by surgery. Each woman had received one or fewer rounds of chemotherapy for the spread. By chance, half got the new drug through an IV every 3 weeks, and half got the chemotherapy their doctor chose. Reviewers who did not know who got which treatment judged whether the cancer had grown. The results were published Oct. 23, 2026, in JAMA, and the trial was open-label, done only in China, and has not yet reported how long women lived.

What they found

The main measure was how long women lived without their cancer growing. Across everyone in the trial, the median was 16.4 months on the new drug and 6.8 months on chemotherapy. (Median means the middle: half the women did better than that, half did worse.)

The result held for women who had never had chemotherapy for the spread, too. They went a median 16.6 months on the new drug vs 6.8 months on chemotherapy.

That last pair of rows matters. The benefit showed up in both main tumor types, so it was not limited to one kind of breast cancer.

Both treatments had side effects. Serious ones happened in 84.1% of women on the new drug and 67.9% on chemotherapy. The most common was a drop in neutrophils, a type of white blood cell that fights infection: 65.2% on the new drug and 54.2% on chemotherapy. Blood counts can be checked with routine tests, which is how care teams keep an eye on this.

What does HER2-low mean?

HER2 is a protein found on the surface of some breast cancer cells. For years, tumors were sorted as HER2-positive or HER2-negative. Then doctors saw that many tumors called “negative” actually carry a small amount of HER2. These are now called HER2-low.

Trastuzumab rezetecan is built for exactly that. It is an antibody-drug conjugate. The antibody finds HER2 on the cancer cell and carries a chemotherapy payload straight to it. Even a small amount of HER2 gives the drug something to grab.

What you can do today

You may not have breast cancer yourself, but you probably know someone who does, or will. Knowing one question can help. If you or someone close to you has metastatic breast cancer that was called HER2-negative, ask the oncologist: “Was the tumor tested for HER2-low, and does that change the treatment options?” The answer is usually written on the pathology report, so you can also look for it there.