CHICAGO ( TheStreet) -- An experimental antibody-drug conjugate therapy from the Genentech unit of Roche ( RHHBY) delayed by more than three months the re-growth of breast cancer compared to the current standard of care, according to a phase III study being presented today at the American Society of Clinical Oncology (ASCO) annual meeting. The drug, known as T-DM1, will be filed for regulatory approval in the U.S. and Europe later this year, Roche said. T-DM1 is a second-generation version of Genentech's blockbuster breast cancer drug Herceptin. The drug consists of Herceptin (also known as trastuzumab) linked to a tumor-killing chemotherapy payload developed by ImmunoGen ( IMGN). The phase III enrolled 1,000 women with advanced, metastatic Her-2 positive breast cancer who were ready for second-line therapy, having been previously treated with Herceptin and chemotherapy. The women were randomized to treatment with either TDM-1 or a combination of Roche's Xeloda and GlaxoSmithKline's ( GSK) Tykerb, which is approved for second-line breast cancer treatment. Breast cancer patients treated with TDM-1 lived a median of 9.6 months before their cancer progressed compared to 6.4 months for the patients treated with the Xeloda-Tykerb combination. The benefit, which equates to a 35% reduction in the risk of disease progression favoring TDM-1, was statistically significant. After two years of follow-up, 65.4% of TDM-1 patients were alive compared to 47.5% of patients treated with Xeloda-Tykerb. This improvement in survival is not yet statistically significant but Genentech continues to follow these patients and additional survival analyses will be conducted, the company said. TDM-1 caused more patients to suffer from reduced platelet counts but the Xeloda-Tykerb combination caused more diarrhea, hand-foot syndrome and vomiting. Sixteen percent of patients had to reduce the dose of TDM-1 during treatment compared to 53% of patients treated with Xeloda-Tykerb. "The drug
TDM-1 worked. It was significantly better than a very effective approved therapy for HER2 overexpressing metastatic breast cancer," said Dr. Kimberly Blackwell, professor of medicine at Duke University's Cancer Institute. "Also, as a clinician who takes care of a lot of breast cancer patients, I’m pleased that this drug has very little dose-limiting toxicity. Patients don't lose their hair from this drug. For patients facing metastatic breast cancer, this is a breakthrough."
If eventually approved, TDM-1 is expected to become a new standard of care for second-line treatment of metastatic, HER2-positive breast cancer, largely supplanting Glaxo's Tykerb, which posted 2011 sales of $372 million. ImmunoGen will receive single-digit royalties pegged to the TDM-1 sales by Genentech in the U.S. and Roche in the rest of the world. Roche continues to study TDM-1 in breast cancer patients with less advanced disease, which may help the company extend the life of its Herceptin franchise, which brought in $5 billion in sales last year. Another Roche drug, pertuzumab, is already filed with FDA, which is expected to issue an approval decision on June 8, just days after oncologists leave the ASCO meeting here. Pertuzumab, which will be sold under the brand name Perjeta, is similar to Herceptin in that it is designed for use in patients with breast cancer that contains an overexpression of HER2 receptors. Perjeta targets HER2 receptors but in a different way than Herceptin. This allows Perjeta to be used in combination with Herceptin or TDM-1. In a pivotal study, the combination of Perjeta, Herceptin and chemotherapy prolonged progression-free survival by six months compared to Herceptin and chemotherapy alone. This study enrolled women with previously untreated HER2-positive metastatic breast cancer. --Written by Adam Feuerstein in Boston. >To contact the writer of this article, click here: Adam Feuerstein. >To follow the writer on Twitter, go to http://twitter.com/adamfeuerstein. >To submit a news tip, send an email to: email@example.com. Follow TheStreet on Twitter and become a fan on Facebook.