A new type of breast cancer treatment has shown encouraging activity as a first-line therapy in HER2-positive metastatic disease.

Edith Perez, Mayo Clinic in Florida, presented the results of the first ever randomized trial of Trastuzumab-DM1 ( T-DM1 ) as a first-line treatment for metastatic breast cancer at the 35th Congress of the European Society for Medical Oncology ( ESMO ) in Milan, Italy.

T-DM1 is the first of a new type of cancer medicine known as an antibody-drug conjugate. It binds together two existing cancer drugs with the aim of delivering both drugs specifically to cancer cells: Trastuzumab ( Herceptin ), a monoclonal antibody that targets cells that overproduce the protein HER2; and DM1, a chemotherapy agent that targets microtubules.

The study demonstrated that T-DM1 has a good anti-tumor activity as well as much lower toxicity when evaluated side by side to the older standard.

T-DM1 has shown promising activity in preclinical studies. Other clinical trials have also shown it to be effective in patients whose advanced cancer has not responded to other treatments.

In the trial, researchers randomly assigned 137 women to treatment with either Trastuzumab plus the chemotherapy drug Docetaxel ( Taxotere ), or T-DM1. All participants had HER2-positive metastatic cancer, with no prior chemotherapy for their metastatic disease.

After a median of approximately 6 months of follow-up, the researchers found an overall response rate of 48% in patients administered T-DM1, compared to 41% in the Trastuzumab plus Docetaxel arm. Importantly, the rates of clinically relevant adverse events were significantly lower in the T-DM1 arm ( 37% ) compared to the rate in women given Traztuzumab plus Docetaxel ( 75% ).

This trial is ongoing and the positive outcomes are generating enthusiasm for a larger phase-III trial which is now underway. This trial is named MARIANNE, and it evaluates taxane plus Trastuzumab against T-DM1 as administered in this study, with a third option being T-DM1 plus Pertuzumab, another novel anti-HER2 agent.

Source: European Society for Medical Oncology, 2010

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