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Antibody guided drug promising for treatment resistant breast cancer

Kathleen Blanchard's picture

Women whose breast cancer had become resistant to chemotherapy responded to a new antibody guided drug that either halted or reduce the size of breast tumors in nearly half of the study participants with HER2-positive cancer. The study comes from early data from a multicenter Phase II clinical trial led by a Dana-Farber Cancer Institute researcher. The women studied had previously received seven different chemotherapy drugs for breast cancer treatment.

The antibody based drug, called T-DM1, reduced tumor size in 40 percent of the women by more than 30 percent. According to ImmunoGen, Inc. "Trastuzumab-DM1 (T-DM1) consists of our DM1 cell-killing agent attached to the HER2-binding antibody, trastuzumab." Approximately 20 percent of all breast cancers are HER2 positive. The study was performed in women who had been given all of the FDA approved drugs available for breast cancer treatment. Breast cancer had progressed despite standard chemotherapy treatment.

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One of the exciting features of the antibody-guided drug is that high doses can be delivered directly to tumor cells to block HER2 receptors. According to Ian Krop, MD, PhD, principal investigator of the study, "The antibody binds to the HER2 protein on tumor cells and delivers the drug (DM1) selectively to them – but not to normal cells. This allows us to deliver high doses of the chemotherapy directly to tumor cells. And at the same time, the antibody continues to block the HER2 growth signals."

The benefit rate for women with chemotherapy and resistant breast cancer was 53 percent overall in women with comfirmed HER2-positive disease. Thirteen percent of the women treated with the antibody based drug had stable HER2-positive breast cancer for six months. A total of 110 women were enrolled in the study. The average time before breast cancer progressed was 7.3 months.

The antibody guided therapy was well tolerated. Side effects of nausea, fatigue, and lower platelet counts, were typically mild. The antibody-guided drug T-DMI is being tested in Phase III clinical trials, in combination with other chemotherapy drugs, and offers new hope for women who have HER2 -positive breast cancer that is resistant to chemotherapy.