Trastuzumab emtansine (T-DM1) worked just as well as taxane plus trastuzumab for first-line treatment in people with HER2-positive, advanced breast cancer in a phase 3 study involving nearly 1,100 individuals. Additionally, it was better tolerated.

Participants—all of whom had not been previously treated for advanced disease—were randomly assigned to receive trastuzumab plus taxane, T-DM1 plus placebo, or T-DM1 plus pertuzumab. Investigators evaluated progression-free survival. Among the results:

• Patients taking T-DM1/placebo and T-DM1/pertuzumab experienced similar progression free survival: ~14 months for both; it was similar in those taking trastuzumab/taxane: ~15 months.
• Response rate was ~68% in patients taking trastuzumab/taxane; it was ~60% with T-DM1/placebo, and ~64% with T-DM1/pertuzumab.
• Median response duration was 12.5 months for trastuzumab/taxane; it was ~21 months in the other 2 groups.
• The incidence of grade ≥3 adverse events was ~54% in the trastuzumab/taxane arm, compared with ~45% in the T-DM1/placebo group and ~46% in the T-DM1/pertuzumab contingent.