Trastuzumab emtansine: a novel antibody-drug conjugate for HER2-positive breast cancer.

INTRODUCTION: Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate (ADC) that combines intracellular delivery of the potent cytotoxic agent, DM1 (a derivative of maytansine) with the antitumor activity of trastuzumab. While there are several ADCs in Phase III development, T-DM1 is the only one in which the targeting antibody has antitumor properties. T-DM1 is also the only ADC that is directed toward the human EGFR 2 (HER2). Effective therapies are limited in HER2-positive advanced or metastatic breast cancer (MBC), particularly following progression on available HER2-targeted therapies. AREAS COVERED: The mechanisms of action, preclinical efficacy and clinical profile of T-DM1 are reported. The latest preclinical and clinical data for T-DM1 are examined. EXPERT OPINION: T-DM1 has significant antitumor potency in vitro and in vivo, which is maintained in tumors resistant to trastuzumab or lapatinib. In Phase I and II trials, T-DM1 provided objective tumor responses and was well tolerated across various lines of therapy in patients with HER2-positive MBC. In addition, it showed similar efficacy to trastuzumab plus docetaxel in first-line MBC. Ongoing trials (including two Phase III studies) are investigating T-DM1 as single-agent therapy or combined with other chemotherapeutic or biologic agents, and the results should help to define the place of T-DM1 within current treatment algorithms for HER2-positive disease.