In February the Food and Drug Administration (FDA) approved ado-trastuzumab emtansine (Kadcyla) to treat late-stage (metastatic) HER2-positive breast cancer. Approximately 20% of breast cancer tumors show elevated levels of the protein HER2. The drug is prescribed to women who've already undergone treatment with trastuzumab as a single agent (Herceptin) and with a drug from the class known as taxanes (such as paclitaxel). Kadcyla is a HER2-targeted, humanized monoclonal antibody and microtubular inhibitor conjugate. It's a combination of the monoclonal antibody trastuzumab and small molecule components. Upon binding to a place on the HER2 receptor, it disrupts microtubule networks in the cell, which results in cell death. Ado-trastuzumab emtansine and trastuzumab are distinct drug entities and cannot be substituted for one another.

A clinical study of 991 patients randomly assigned to receive Kadcyla or lapatinib (one of the targeted therapies from the drug class known as kinase inhibitors) combined with capecitabine (an antimetabolite chemotherapeutic agent) measured both progression-free survival and overall survival. Kadcyla's effects on both were modest but statistically significant. Patients treated with Kadcyla had a median progression-free survival of 9.6 months, compared with 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.

Kadcyla's label carries a boxed warning that the drug can cause hepatotoxicity; cardiac toxicity (including fatal); and embryotoxicity or fetotoxicity, which can result in death or birth defects. Common adverse effects-those occurring in more than 25% of patients-are nausea, fatigue, musculoskeletal pain, thrombocytopenia, elevated levels of liver enzymes (transaminases), headache, and constipation.

Nurses administering Kadcyla intravenously should assess hepatic function before each infusion and notify the prescribing physician if hepatotoxicity is suspected. Because Kadcyla can decrease left ventricular ejection fraction, nurses should assess it before the drug is started and notify the prescribing physician if a reduction in left ventricular function is present. Nurses should also ensure that there's no possibility of pregnancy before administration of the first dose. Patient education should include the signs and symptoms of liver toxicity (such as right upper-quadrant pain, jaundice, and dark-colored urine), the signs and symptoms of cardiac toxicity (such as shortness of breath, cough, swelling of the ankles or legs, palpitations, or weight gain of more than 5 lbs. in 24 hours), and the importance of birth control during therapy with Kadcyla.

Complete FDA prescribing information can be found at http://1.usa.gov/17vPfZc.