Breast cancer drug shown to prolong patients’ lives

CHICAGO — A drug that delivers a powerful poison to tumors without some of the side effects of traditional treatments can delay the worsening of breast cancer and also appears to substantially prolong lives, according to results of a study.

Besides representing an advance in treating breast cancer, the success in the clinical trial validates an idea that is now being pursued by numerous pharmaceutical companies to treat various types of cancer in a way that delivers drugs to cancerous cells while sparing healthy ones.

“We’ve envisioned a world where cancer treatment would kill the cancer and not hurt the patient,” said Dr. Kimberly Blackwell, professor of medicine at the Duke Cancer Institute and the lead investigator in the trial. “And this drug does that.”

The drug, known as T-DM1, was developed by Genentech in South San Francisco, which sponsored the trial. The company plans to file for approval this year. Results of the study are to be formally presented Sunday at the American Society of Clinical Oncology meeting in Chicago.

T-DM1 and similar drugs under development consist of powerful toxins linked to proteins called antibodies. The antibodies latch onto cancer cells and deliver the toxic payload directly into those cells.

The late-stage clinical trial involved 991 women with metastatic breast cancer whose cancer was worsening despite treatment with the drug Herceptin and a chemotherapy drug called a taxane. Half the women got T-DM1 and the other half received two drugs that are now commonly used for such patients.

T-DM1 delayed the worsening of disease by about three months. For those who received T-DM1, the median time before the disease progressed was 9.6 months, compared with 6.4 months for those getting the two other drugs.

The median survival for those getting T-DM1 is not yet known. But Blackwell said it would probably be at least a year longer than the 23.3-month median survival for the women in the control group.