Comparative effectiveness of trastuzumab emtansine versus lapatinib plus chemotherapy for HER2+ metastatic breast cancer.

To investigate the comparative effectiveness of trastuzumab emtansine (T-DM1) in a real-world population of HER2+ metastatic breast cancer (mBC) patients. The Flatiron Health database was used to identify a cohort of HER2+ mBC patients who received first-line trastuzumab treatment and T-DM1 or lapatinib plus chemotherapy as second-line treatment. Overall survival was compared between the two groups.  A total of 278 patients with HER2+ mBC received second-line T-DM1 and 34 lapatinib plus chemotherapy. Overall survival was longer in patients treated with T-DM1 than those treated with lapatinib plus chemotherapy (adjusted hazard ratio: 0.56; 95% CI: 0.38-0.85). Real-world data supports the effectiveness of T-DM1 in the second-line treatment of HER2+ mBC patients.