A targeted drug added about 5 months of life in one breast cancer, trial finds

Chemotherapy has an old problem. The drugs that kill fast growing cancer cells also hit healthy ones, from hair roots to the lining of the gut. For decades, researchers have tried to send the drug straight to the tumour instead, a bit like putting an address label on a parcel [1].

One treatment built that way was tested in 468 adults with a hard to treat breast cancer that had spread. The typical patient on it lived 12.1 months, against 6.7 months for the typical patient on a standard chemotherapy. That is about five months longer [1].

The main catch is worth saying early. When the same treatment was later tried in 711 adults with advanced cancer of the bladder and urinary tract, it did not help people live longer. More of them also died from side effects [3].

The treatment is called sacituzumab govitecan. It joins a chemotherapy drug to an antibody, a protein the immune system makes to lock onto one exact target. This antibody looks for Trop-2, a protein found on the outside of most breast cancer cells. The antibody is the address, and the chemotherapy is what is inside the parcel [1].

The first trial, called ASCENT, was led by Aditya Bardia of the Massachusetts General Hospital Cancer Center in Boston. It was published in the New England Journal of Medicine in 2021 and paid for by Immunomedics, the company that first made the drug [1].

Its patients had triple negative breast cancer. That means the tumour lacks three receptors, small switches on the cell, that most breast cancer medicines aim at. Their cancer had come back or stopped responding, and all had already had a chemotherapy called a taxane. Chance decided, like a coin flip, who got the new treatment and who got one chemotherapy drug their doctor picked [1].

Besides living longer, people on the new treatment went longer before their cancer grew again. For the typical patient, that was 5.6 months, against 1.7 months on chemotherapy. Tumours shrank clearly in about 1 in 3 people on the new treatment, against 1 in 20 on chemotherapy [1].

The researchers summed up the trial this way:

Progression-free and overall survival were significantly longer with sacituzumab govitecan than with single-agent chemotherapy among patients with metastatic triple-negative breast cancer.

In plain words, people on the targeted treatment went longer before the cancer grew, and lived longer, than people on one standard chemotherapy drug. The trade off was harder side effects. About half had very low counts of white blood cells, the cells that fight germs, against about a third on chemotherapy. Bad diarrhoea hit about 1 in 10, against fewer than 1 in 100 [1].

Three people in each group died from side effects. None of those deaths were blamed on the new treatment [1].

Does it work in other cancers too?

A second trial, TROPiCS-02, was led by Hope Rugo of the University of California San Francisco and paid for by Gilead Sciences. It was published in The Lancet in 2023. It tested the treatment in 543 adults with a more common breast cancer, one driven by hormone receptors, who had already tried several other treatments [2].

The gain was smaller there. The typical patient lived 14.4 months on the new treatment, against 11.2 months on chemotherapy, a gap of 3.2 months. One death, from a severe infection while white cell counts were low, was judged to be caused by the treatment [2].

The third trial, TROPiCS-04, came from a team led at Barts Cancer Institute, Queen Mary University of London, and several of its authors work for Gilead. It was published in Annals of Oncology in 2025. Its 711 adults had bladder and urinary tract cancer that had kept growing after earlier treatments [3].

Here the typical patient lived 10.3 months on the new treatment, against 9.0 months on chemotherapy. That gap was too small to rule out chance. Tumours did shrink more often, in 23 percent of people against 14 percent. But serious side effects hit about two in three people on the new treatment, against about one in three on chemotherapy. Deaths from side effects were 7 percent against 2 percent [3].

The authors offer one reason for the result:

Early toxicity-related complications with SG may have impacted efficacy outcomes.

In plain words, harm from the drug early in treatment may have wiped out any gain. Sixteen of the 25 deaths from side effects in that group were infections while white cell counts were low. Most came early, in people who already had several risk factors for exactly that problem [3].

So what do the three trials add up to? The same antibody, aimed at the same target, gave three answers. There was a clear gain in one breast cancer, a smaller gain in another, and no clear gain in bladder cancer. Carrying the target protein is not, on its own, a reason to expect the drug to help [1][2][3].

These trials do not show a cure. They also do not show how the treatment compares with newer medicines, since each one was measured only against older chemotherapy. What they do show is narrower. In one group of people with breast cancer, at one point in their illness, a drug sent to the tumour helped the typical patient live about five months longer [1][2][3].