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    'Magic Bullet' Drug Delays Breast Cancer Worsening

    T-DM1 Spares Women From Some, But Not All, Serious Side Effects

    How T-DM1 Works continued...

    But many metastatic breast cancers eventually become resistant to Herceptin. So researchers have been searching 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.

    Because Herceptin only zeroes in on cancer cells that express HER2, DM1 is delivered only to those cells, Blackwell says.

    "I think this will offer a very important therapeutic option for patients with HER2-positive metastatic breast cancer," she says. "I think it's the first of many antibody-drug [combinations] to follow that will link a potent anti-cancer agent to a targeted delivery system with an antibody."

    About two dozen similar drugs, collectively known as antibody-drug conjugates, are in various stages of development, according to Louis M. Weiner, MD, director of the Lombardi Comprehensive Cancer Center at Georgetown University.

    T-DM1 is a "magic bullet," Weiner says. He likens it to a Trojan horse that is welcomed into the cell while hiding something that is toxic to the cell.

    The drug is made by Genentech, which funded the trial. The company plans to file for FDA approval later this year.

    No cost has been set, but targeted cancer drugs often cost tens of thousands of dollars a month.

    These findings were presented at a medical conference. They should be considered preliminary, as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.

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