ImmunoGen and Roche say that their promising antibody-drug conjugate breast cancer treatment, T-DM1, met its primary endpoint in a late-stage trial by extending the lives of patients with metastatic cancer, encouraging the partners to submit the drug to U.S. and European regulators for marketing approval.

The companies did not say how much longer patients lived when treated with T-DM1 than patients given competing therapies, however ImmunoGen said that there was a “significant improvement in overall survival.” The late-stage trial compared T-DM1 to GlaxoSmithKline’s Tykerb and Genentech’s Xeloda, both of which are approved for the treatment of breast cancer.
“We are extremely pleased to announce that people treated with [T-DM1] survived significantly longer than those who received a standard option for this aggressive advanced breast cancer,” says Roche’s CMO. “We believe that antibody-drug conjugates have the potential to change the future treatment of cancer.”

T-DM1 combines trastuzumab, the active ingredient in Roche’s breast cancer drug Herceptin, with ImmunoGen’s Targeted Antibody Payload technology, a monoclonal antibody combined with a powerful cancer killing agent, and gets delivered directly to the tumor cells, bypassing healthy cells.

Antibody-drug conjugates have long been touted as a promising treatment for cancer, a “magic bullet” that could zero in on tumor cells while avoiding the destruction of healthy cells by linking cell-killing small molecule drugs with antibodies that target cancer cells.

The first antibody-drug conjugate to be approved by the U.S. Food and Drug Administration was Mylotarg in 2000, but it was ultimately pulled from the market in 2010 after safety concerns arose in post-marketing studies. It took more than a decade for another antibody-drug conjugate to make it to market, Seattle Genetics’ Adcetris.

Roche has submitted a Biologics License Application to market of T-DM1 in the United States and is planning to submit a Marketing Authorization Application to the European Medicines Agency later this year.

Cowen & Co. analyst Simos Simeonidis stated that he expects an FDA approval of T-DM1 in the first half of 2013 and foresees sales approaching Herceptin’s sales numbers ($5.4 billion in 2011) if the treatment is successful in all of its late-stage trials.

ImmunoGen stands to gain a lot from T-DM1’s approval. Any future sales of the therapy will provide ImmunoGen with royalty payments and can help endorse its TAP technology.