Genentech’s Souped-Up Breast Cancer Drug Beats Original Herceptin in Head-to-Head Study

Xconomy San Francisco — 

Genentech broke new ground with a targeted antibody drug for breast cancer in the late 1990s, and now it’s showing another sign that it may have surpassed the original.

Researchers reported today on a study of 137 breast cancer patients who were randomly assigned to get the original trastuzumab (Herceptin) along with chemotherapy, or a new souped-up antibody drug called T-DM1 from South San Francisco-based Genentech and Waltham, MA-based ImmunoGen (NASDAQ: IMGN). The study, among women getting their first round of therapy, showed that 48 percent had tumor shrinkage on the new drug, while 41 percent did that well on standard treatment. Even more interesting, only 37 percent of women on the new drug had clinically relevant adverse events, compared with 75 percent on the standard therapy. The data was presented at the European Society for Medical Oncology in Milan, Italy.

This is still just a mid-stage clinical trial, and researchers still don’t know if the new drug is any better at keeping tumors from spreading—the main goal of the study. But it’s another intriguing step forward for T-DM1, which is seeking to blaze a new trail as the one of the first drugs to ever successfully combine the precise targeting capability of an antibody with a super-potent toxin to kill tumor cells. This is a scientific concept that no one has been able to really pull off over the last three decades, but Genentech is betting that the new drug will improve upon the original, which now generates more than $5 billion in annual worldwide sales.

“We are encouraged by the results,” said Edith Perez, a researcher at the Mayo Clinic in Florida, and the lead investigator of the trial, in a statement. “The study demonstrated that T-DM1 has very good anti-tumor activity as well as much lower toxicity when evaluated side by side to the older ‘standard’.”

Genentech had hoped to win FDA approval of T-DM1 based on a separate study that showed promising tumor-shrinkage results in much sicker patients who were getting their third round of therapy. But in August Genentech was dealt a setback when the FDA said it wouldn’t consider that application for a faster-than-usual approval, meaning that Genentech would have to wait for results from a pivotal stage trial of about 580 patients, called Emilia, which started in March 2009. That study continues to gather data on very sick patients whose disease has worsened after prior therapy. Genentech is also testing its new drug in a study of more than 1,000 patients, called Marianne, who are getting their initial round of treatment.

One of key questions will be whether T-DM1 is a potent enough drug to enable doctors to quit using standard chemotherapy that circulates through the body, causing side effects. While today’s results aren’t enough to definitively say the mission has been accomplished, Genentech spokeswoman Krysta Pellegrino says it “supports the rationale” for developing T-DM1.

“We continue to think the drug works,” Pellegrino says.