Kadcyla® (T-DM1 or ado-trastuzumab emtansine), a new treatment for patients with HER2-positive, metastatic breast cancer to be marketed by Roche’s Genentech subsidiary, won FDA approval this morning.

Kadcyla is a trastuzumab-DM1 antibody-drug conjugate intended for patients previously treated with Herceptin® (trastuzumab), another anti-HER2 therapy, and taxanes, a class of chemotherapy drugs commonly used for the treatment of breast cancer. The newly-approved drug is a combination of Herceptin and DM1, which Kadcyla delivers to the cancer site, shrinking the size of the tumor, slowing disease progression, and prolonging overall survival.

The fourth FDA-approved drug that targets the HER2 protein, Kadcyla was developed by ImmunoGen, and joins three other HER2-positive breast cancer treatments approved in the past decade and a half: trastuzumab (1998), lapatinib (2007), and pertuzumab (2012). Like Kadcyla, trastuzumab and pertuzumab are made by Roche’s Genentech subsidiary.

However, ImmunoGen will yet benefit from Kadcyla’s approval. While the company was rebuffed by FDA nearly three years ago when it sought fast-track review for the drug, ImmunoGen will receive a $10.5 million milestone payment from Roche, as well as royalties on commercial sales of Kadcyla.

In 2000, nine years before its acquisition by Roche, Genentech licensed from ImmunoGen exclusive rights to use the company’s maytansinoid TAP technology to develop anticancer products targeting HER2. Six years later, Genentech advanced T-DM1/Kadcyla into clinical testing.

Kadcyla won FDA approval through the agency’s priority review program, which allows a speedier six-month review of drugs judged as having potential to provide safe and effective therapy when no satisfactory alternative therapy exists, or offer significant improvement compared to marketed products.

FDA based its decision on safety and effectiveness results from a clinical trial of 991 patients randomly assigned to receive T-DM1 or GlaxoSmithKline’s lapatinib plus another chemotherapy drug, capecitabine. Patients treated with T-DM1 had a median progression-free survival of 9.6 months compared to 6.4 months in patients treated with lapatinib plus capecitabine. The median overall survival was 30.9 months in the T-DM1 group and 25.1 months in the lapatinib plus capecitabine group.

During the trial, patients received treatment until either the cancer progressed or the side effects became intolerable. The study was designed to measure progression-free survival (the length of time patients lived without the cancer progressing) and overall survival (the length of time patients lived before death).

However, T-DM1 is being approved with a Boxed Warning alerting patients and health care professionals of the drug’s potential side effects, which include liver toxicity, heart toxicity, and death. The drug can also cause severe life-threatening birth defects, and pregnancy status should be verified prior to starting treatment, the warning cautions.

In patients treated with T-DM1, the most common side effects were nausea, fatigue, pain in the muscles or joints, low levels of platelets in the blood (thrombocytopenia), increased levels of liver enzymes, headache, and constipation.

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