Results from the phase III EMILIA trial presented at the ASCO plenary session could mean a new treatment option for women with HER2-positive tumours that might avoid the usual adverse effects of chemotherapy. Trastuzumab emtansine (T-DM1), an antibody–drug conjugate of trastuzumab and DM1, provides both antitumour activity and targeted delivery. Patients with progressive disease or metastasis who had previously been treated with a taxane and trastuzumab were randomly assigned to T-DM1 or capecitabine plus lapatinib—the only approved therapy for patients with trastuzumab-refractory breast cancer.

T-DM1 was associated with a significant improvement in progression-free survival (9.6 versus 6.4 months). Overall survival was not reached in the T-DM1 arm and was 23.3 months in the capecitabine plus lapatinib arm. Subgroup analyses showed that T-DM1 was better for all groups except those aged 65 or older. Importantly, the safety of T-DM1 was considerably superior to capecitabine and lapatinib. Dose reduction was required in only 16.3% of patients receiving T-DM1, whereas the capecitabine and lapatinib doses were reduced for 53.4% and 27.3% of patients, respectively.

The time to symptom progression was also much longer for T-DM1 compared with capecitabine and lapatinib. Notably, the incidence of adverse events was lower for patients treated with T-DM1, and cardiac toxicity was not increased with this agent. T-DM1 is an active, well tolerated novel therapy with a clinically meaningful improvement in outcome.