HealthDay News — The FDA has approved ado-trastuzumab emtansine (Kadcyla, Genentech), the fourth treatment approved for patients with human epidermal growth factor receptor 2 (HER2)-positive, metastatic breast cancer.

Ado-trastuzumab emtansine is indicated for patients who were previously treated with trastuzumab, another anti-HER2 therapy, and taxanes, a class of chemotherapy drugs commonly used for the treatment of breast cancer.

“Kadcyla is trastuzumab connected to a drug called DM1 that interferes with cancer cell growth,” Richard Pazdur, MD, director of the Office of Hematology and Oncology Products in the FDA’s Center for Drug Evaluation and Research, said in a press release. “Kadcyla delivers the drug to the cancer site to shrink the tumor, slow disease progression and prolong survival.”

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The approval was based on safety and effectiveness data from a clinical study that involved 991 patients randomly assigned to receive Kadcyla or lapatinib plus capecitabine. Patients received treatment until either the cancer progressed or the side effects became intolerable.

Patients treated with Kadcyla had a median progression-free survival of 9.6 months vs. 6.4 months in patients treated with lapatinib plus capecitabine. The median overall survival was 30.9 months and 25.1 months in the two groups, respectively.

Kadcyla will carry a boxed warning to alert patients and clinicians that the drug can cause liver toxicity, heart toxicity and death, the FDA stated.

The drug can also cause severe life-threatening birth defects, and pregnancy status should be verified prior to drug initiation. The most common side effects reported were nausea, fatigue, muscle or joint pain, thrombocytopenia, increased levels of liver enzymes, headache, and constipation.