The drug-antibody conjugate was more effective and less toxic than lapatinib plus capecitabine in patients previously treated with trastuzumab and a taxane.

We can expect that the next breast cancer drug soon to be approved by the FDA will be trastuzumab emtansine (T-DM1), an antibody-drug conjugate combining trastuzumab with a derivative of the cytotoxic maytansine via a stable linker molecule (JW Oncol Hematol Oct 2 2012). T-DM1 is more than just another new agent. It represents vindication for those who have worked on fusion molecules for the last 2 decades. Previous efforts with such molecules were often derailed because the linker was either unstable (resulting in systemic exposure to the toxin) or cytotoxic (resulting in prohibitive adverse effects). With T-DM1, intracellular drug delivery only to human epidermal growth factor receptor 2 (HER2)–overexpressing tumor cells has been observed.

Now, investigators report the results of the EMILIA study, an industry-sponsored, phase III, randomized, open-label trial involving 991 patients with HER2-positive, unresectable, locally advanced or metastatic breast cancer who were previously treated with trastuzumab and a taxane. Patients received either T-DM1 or lapatinib plus capecitabine (LC) and were stratified by world region, number of prior chemotherapy regimens for advanced disease, and presence or absence of visceral disease. Primary endpoints were progression-free survival (PFS), overall survival (OS), and safety; secondary endpoints included objective response rate, duration of response, and time to symptom progression.

Median PFS was significantly longer with T-DM1 versus LC (9.6 vs. 6.4 months; hazard ratio, 0.65; P<0.001), as was median OS (30.9 vs. 25.1 months; HR, 0.68; P<0.001). Overall response rate was also superior with T-DM1 versus LC (43.6% vs. 30.8%; P<0.001), as were results for all secondary endpoints. Rates of grade 3 or 4 adverse events were 40.8% with T-DM1 and 57.0% with LC.

Comment: The excitement surrounding the anticipated FDA approval of T-DM1 is justified given that the drug successfully targets HER2-overexpressing disease with potent antitumor activity minus the full complement of adverse effects associated with typical chemotherapy partnered with trastuzumab. Of course, the stage is set for exploring T-DM1 in combination with other anti-HER2 agents, including pertuzumab (JW Oncol Hematol Jan 24 2012). Because the toxicity of T-DM1 is quite modest, adjuvant trials are under way to compare the use of this compound with standard trastuzumab-based regimens.

Source: Journal Watch Oncology and Hematology