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Genentech, ImmunoGen’s Souped-Up Antibody for Breast Cancer Passes Key Test

Xconomy San Francisco — 

The evidence is mounting to prove the point that Genentech’s scientists have been trying to make for years—that a souped-up version of its top-selling antibody drug for breast cancer can be more effective in some cases than the original.

Genentech, the South San Francisco-based unit of Roche, and its partner, Waltham, MA-based ImmunoGen (NASDAQ: IMGN), are announcing today that their experimental drug trastuzumab emtansine reached its main goal. This study enrolled 137 breast cancer patients with a mutated form of the HER2 protein who were getting a first round of treatment for disease that had spread. The trial showed that patients on the new drug (T-DM1) were alive and able to keep their tumors from further spreading for a median of 14.2 months, compared with 9.2 months for those who were randomly assigned to the standard trastuzumab (Herceptin) and chemotherapy.

What’s equally, if not more, interesting is that patients on the new medicine also reported about half as many cases of moderate to severe side effects—about 46.4 percent on the new medicine, compared with 89.4 percent on the standard drugs. And only 7.2 percent of patients on the new drug dropped out of the study because of adverse events, compared with 28.8 percent on the standard treatments.

The results are being reported today at the European Multidisciplinary Cancer Congress in Stockholm, Sweden. Hal Barron, Genentech’s chief medical officer, called the results “very exciting” in a company statement.

“Herceptin is a great drug, but we think we can be doing even more for patients,” says Genentech spokeswoman Krysta Pellegrino.

The results come from a mid-stage clinical trial, so Genentech still has to bolster its case through a series of ongoing pivotal trials before this drug can be cleared for sale by the FDA. But it’s an important step in the journey for this new drug, which is seeking to become part of an emerging class of therapies that combine an antibody’s ability to zero in specifically on cancer cells along with a toxin that’s supposed to deliver a knockout punch to tumors. If Genentech can confirm these results in these pivotal studies, then it could be in position to seek FDA approval for this “supercharged” version of Herceptin. The original has been a huge boon to the company, producing more than $5 billion in annual worldwide sales, and analysts predict this new version will be huge, too. ImmunoGen, which helped develop the technology to link the antibody to the toxin, stands to collect royalties on worldwide sales if the new drug reaches the market.

About one year ago, researchers reported some interim results that hinted that Genentech was on the right track with this drug. Back then, researchers said that 48 percent of patients on the new medicine appeared to have their tumors shrink, compared with 41 percent on the standard treatments. Upon further follow-up, scientists said that 64 percent on the new drug had their tumors shrink, compared with 58 percent in the control group.

One of the secondary goals of the study is to see whether patients live longer on the new treatment or not. There isn’t enough data yet from the trial to answer that question—which is the gold standard measurement of success in cancer drug development. Genentech said that so far, the number of deaths in each treatment group has been identical, and that investigators don’t consider any of the deaths to be drug-related.

Those who have been following this story closely will remember that Genentech was turned down by the FDA one year ago when it sought accelerated approval to start selling T-DM1. That application was based on a much thinner body of evidence, primarily a study that measured tumor shrinkage rates—an often important, but sometimes unreliable indicator of success—in 110 patients. Patients in that study were very sick, they were only getting the new medicine, and there was no group getting another viable therapy or placebo for comparison.

When the FDA asked for more data in August 2010, it put more of the focus on the trial being reported on today, known as 4450, and a pivotal trial of more than 1,000 patients with a similar design, called Marianne. Another study, called Emilia, is enrolling as many as 980 patients to answer a slightly different question. Those patients will be getting their second round of therapy, and they will be randomly assigned to get either the new souped-up antibody or a combination of GlaxoSmithKline’s lapatinib (Tykerb) and capecitabine (Xeloda) chemotherapy.

The Emilia trial, which could be the basis of another application to the FDA, could generate results in 2012, Pellegrino says.

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