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 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 important, 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 alive, versus 47 percent of those in a comparison group given two standard cancer drugs.
That margin fell just short of the strict criteria researchers set for stopping the study and declaring the new treatment a winner, and they hope the benefit becomes more clear with time. In fact, so many women on the new treatment are 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 experimental and 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, called T-DM1, is the “smart bomb,” although it is not all that smart — Herceptin isn’t a homing device, just a substance that binds to breast-cancer cells once it encounters them.
Doctors tested T-DM1 in 991 women with widely spread breast cancer that was getting worse despite treatment with chemotherapy and ordinary Herceptin. They were given either T-DM1 infusions every three weeks or infusions of Xeloda plus daily Tykerb pills — the only other treatments approved for such cases.
The median time until cancer got worse was nearly 10 months in the women given T-DM1 versus just over six months for the others. That is about the same magnitude of benefit initially seen with Herceptin, which later proved to improve overall survival too, Blackwell said.
T-DM1 caused fewer side effects than the other drugs. 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 for Genentech, the study’s sponsor.
Genentech, part of the Swiss company Roche, says the price of T-DM1 has not been determined. Herceptin costs more than $4,000 a month.
