Dec. 15, 2009 (San Antonio) -- A new targeted cancer drug has been shown to
shrink tumors in women with metastatic breast cancer after an average of seven
other drugs, including Herceptin, failed.
The new drug, called T-DM1, combines Herceptin with a potent chemotherapy
drug. It's a Trojan horse approach, where Herceptin homes in on cancer cells
and delivers the cancer-killing agent directly to its target.
Tumors shrank in one-third of women with metastatic breast cancer given
T-DM1, says Ian Krop, MD, of the Dana-Farber Cancer Institute in Boston. In
another 12%, tumors stopped growing for at least six months.
The women remained cancer-free for an average of seven months -- results
unheard of in patients this sick, he says.
All the women, who had breast tumors for an average of three years, had
cancer that had metastasized, or spread to other parts of the body. They had
been treated with an average of seven different therapies, including Herceptin,
Tykerb, and Xeloda, and each had failed.
"This is the first study looking at women who have failed so many other
treatments," Krop tells WebMD. "But we think these results are as good as we've
ever seen is such a refractory [sick] population," he says.
The findings were presented at the San Antonio Breast Cancer Symposium.
About 20% of breast cancer patients have HER2-positive cancers -- tumors
that have too much of a type of protein called HER2. Herceptin, a man-made
antibody, binds to and blocks the HER2 receptor that appears on the surface of
some breast cancer cells.
But metastatic breast cancer eventually becomes resistant to Herceptin. So
researchers have searched for new drugs that target HER2.
T-DM1 is such a drug. The "T" stands for trastuzumab, the scientific name
for Herceptin. The "DM1" is derived from an old chemotherapy drug called
maytansine that was abandoned several decades ago when it was found to be too
toxic for patients, Krop says.
Because Herceptin only zeroes in on cancer cells that express HER2, DM1 is
delivered only to those cells, he says.
"The cytotoxic drug goes right to the cancer cells, so it’s not floating
around and causing other problems. And Herceptin still does all the things that
Herceptin does" to fight cancer, Krop says.