Dr. Richard Pazdur of the FDA's Center for Drug Evaluation and Research said HER2 is a protein involved in normal cell growth and found in increased amounts on some types of cancer cells.
Kadcyla -- ado-trastuzumab emtansine -- is intended for patients 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," Pazdur said in a statement. "Kadcyla delivers the drug to the cancer site to shrink the tumor, slow disease progression and prolong survival."
A clinical study of 991 patients were randomly assigned to receive Kadcyla or lapatinib plus capecitabine, another chemotherapy drug.
The trial showed patients treated with Kadcyla had a median progression-free survival -- time cancer did not progress -- 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 Kadcyla group and 25.1 months in the lapatinib plus capecitabine group, the trial found.
The drug will have an estimated monthly cost of $9,800, or about $94,000 for a full course of treatments, Forbes magazine reported.