Cancer drug effective with fewer side effects

CHICAGO – Doctors have successfully dropped the first “smart bomb” on breast cancer, using a drug to deliver a toxic payload to tumor cells while leaving healthy ones alone.

In a key test involving nearly 1,000 women with very advanced disease, the experimental treatment extended by several months the time women lived without their cancer getting worse, doctors planned to report today at a cancer conference in Chicago.

More importantly, the treatment seems likely to improve survival; it will take more time to know for sure. After two years, 65 percent of women who received it were still alive versus 47 percent of those in a comparison group given two standard cancer drugs.

That margin fell just short of the very strict criteria researchers set for stopping the study and declaring the new treatment a winner, and they hope the benefit becomes clearer with time. In fact, so many women on the new treatment are still alive that researchers cannot yet determine average survival for the group.

“The absolute difference is greater than one year in how long these people live,” said the study’s leader, Dr. Kimberly Blackwell of Duke University. “This is a major step forward.”

A warning to hopeful patients: the drug is still experimental, and so not available yet. Its backers hope it can reach the market within a year.

The treatment builds on Herceptin, the first gene-targeted therapy for breast cancer. It is used for about 20 percent of patients whose tumors overproduce a certain protein.

Researchers combined Herceptin with a chemotherapy so toxic that it can’t be given by itself, plus a chemical to keep the two linked until they reach a cancer cell where the poison can be released to kill it.

This double weapon is called T-DM1.

T-DM1 caused fewer side effects than the other drugs did. Some women on T-DM1 had signs of liver damage and low levels of factors that help blood clot, but most did not have the usual problems of chemotherapy.

“People don’t lose their hair, they don’t throw up. They don’t need nausea medicines, they don’t need transfusions,” said Blackwell, who has consulted in the past for Genentech, the study’s sponsor.

“The data are pretty compelling,” said Dr. Michael Link, a pediatric cancer specialist at Stanford University who is president of the American Society of Clinical Oncology.