Trastuzumab emtansine: determining its role in management of HER2+ breast cancer.

Trastuzumab emtansine is an antibody-drug conjugate comprised of the anti-HER2 monoclonal antibody trastuzumab linked to DM1 (emtansine), a potent cytotoxic maytansinoid derivative, by a stable linker. This structure results in improved tumor-directed cytotoxicity in HER2+ breast cancer with reduced systemic toxicities, particularly the cardiac toxicities associated with single agent trastuzumab. Phase III trials have demonstrated improved progression-free and overall survival in heavily pretreated patients with advanced HER2+ breast cancer, with an acceptable toxicity profile. However, its role in first-line treatment is less clear. Ongoing studies continue to evaluate its role in neoadjuvant and adjuvant management of HER2+ breast cancer.