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

Aim: To investigate the comparative effectiveness of trastuzumab emtansine (T-DM1) in a real-world population of HER2+ metastatic breast cancer (mBC) patients. Materials and methods: 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 capecitabine as second-line treatment. Overall survival was compared between the two groups. Results: Three hundred and forty-five patients with HER2+ mBC received second-line T-DM1 and 65 lapatinib plus capecitabine. Overall survival was longer in patients treated with T-DM1 than those treated with lapatinib plus capecitabine (adjusted hazard ratio: 0.61; 95% CI: 0.41-0.91). Conclusion: Real-world data supports the effectiveness of T-DM1 in the second-line treatment of HER2+ mBC patients. Lay abstract: EMILIA was a randomized clinical trial (RCT) - a type of study designed to test whether a treatment works in a particular disease, using methods to remove possible bias. The study showed that a treatment called trastuzumab emtansine (shortened to T-DM1) improved the survival of patients with a particular type of breast cancer, known as HER2+ metastatic breast cancer (mBC). However, as clinical trials are run under controlled conditions, they do not fully reflect results under normal circumstances. In this study, we looked at the effect of treating a 'real' population of HER2+ mBC patients with T-DM1 in the USA. We found that T-DM1 still improved survival in these 'real-world' patients. Studies in the 'real world' can have some bias, as they are not controlled like RCTs; however, taking the results of the EMILIA RCT, along with the results of our study, supports the use of T-DM1 as a treatment option for HER2+ mBC patients.