Drug trial yields ‘unheard-of ’ results

The patients had metastatic breast cancer that had been progressing despite rounds of harsh chemotherapy. But a treatment with a drug that targeted cancer cells with laserlike precision was stunningly successful, slowing tumor growth and extending life to an extent rarely seen with advanced cancers.

The new study, presented at the annual meeting of the American Society of Clinical Oncology and published Sunday in the New England Journal of Medicine, would change how medicine was practiced, cancer specialists said.

“This is a new standard of care,” said Dr. Eric Winer, head of the ASCO. Winer was not involved with the study.

The trial focused on a particular mutant protein, HER2, which is a common villain in breast and other cancers. Drugs that block HER2 have been stunningly effective in treating breast cancers that are almost entirely populated with the protein. But Her2-positive cases constitute only about 15 percent to 20 percent of breast cancer patients, said Dr. Halle Moore of the Cleveland Clinic. Patients with only a few HER2 cells — a condition known as Her2-low — were not helped by those drugs.

The clinical trial involved 557 patients with metastatic breast cancer who were Her2-low. Two-thirds took the experimental drug, trastuzumab deruxtecan, sold as Enhertu; the rest underwent standard chemotherapy.

In patients who took trastuzumab deruxtecan, tumors stopped growing for about 10 months, as compared with five months for those with standard chemotherapy. The patients with the experimental drug survived for 23.9 months, as compared with 16.8 months for those who received standard chemotherapy. “It is unheard-of for chemotherapy trials in metastatic breast cancer to improve survival in patients by six months,” Moore said.