Among women with metastatic, HER2-positive breast cancer, trastuzumab emtansine (T-DM1)—an investigational drug that combines Herceptin® (trastuzumab) and a chemotherapy drug—resulted in better progression-free survival than standard chemotherapy and Herceptin. The results of this Phase II clinical trial were presented at the 2011 European Multidisciplinary Cancer Congress.

Approximately 20-25% of breast cancers overexpress (make too much of) the HER2 protein. HER2-targeted therapies such as Herceptin have dramatically improved outcomes for women with HER2-positive breast cancer, but researchers continue to explore new approaches to treatment.

T-DM1 links Herceptin with a chemotherapy drug (DM1). T-DM1 delivers Herceptin and DM1 directly to HER2-positive cells, and limits exposure of the rest of the body to the chemotherapy.

To evaluate T-DM1 for the initial treatment of metastatic, HER2-positive breast cancer, researchers conducted a Phase II clinical trial among 137 women. Study participants were treated with either T-DM1 or Herceptin plus Taxotere® (docetaxel).

  • Survival without cancer progression was 14.2 months among women in the T-DM1 group and 9.2 months among women in the Herceptin plus Taxotere group.
  • In addition to delaying cancer progression, T-DM1 was also better tolerated by patients. Discontinuation of treatment due to side effects occurred in 7.2% of women in the T-DM1 group and 28.8% of women in the Herceptin plus Taxotere group.

These results suggest that T-DM1 may be safe and effective for the treatment of advanced, HER2-positive breast cancer. Results from ongoing Phase III trials will provide additional information about this drug.

Reference: Hurvitz S, Dirix L, Kocsis J et al. Trastuzumab emtansine (T-DM1) vs trastuzumab plus docetaxel (H+T) in previously untreated HER2-positive metastatic breast cancer (MBC): primary results of a randomized, multicenter, open-label phase II study (TDM4450g/BO21976). Presented at the 2011 European Multidisciplinary Cancer Conference. Stockholm, Sweden. September 23-27, 2011. Abstract 5001.

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