Survival outcomes in patients with human epidermal growth factor receptor 2 positive metastatic breast cancer administered a therapy following trastuzumab emtansine treatment

Since 2013, trastuzumab emtansine (T-DM1) has been widely used in Japan to treat patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC) who were previously administered trastuzumab and a taxane. However, there is no information about the treatment outcomes after exposure to T-DM1 in Japanese patients with HER2-positive MBC. In this study, we aimed to describe the survival outcomes of patients with HER2-positive MBC who received a treatment following T-DM1 and clarify the predictive factors of their prognosis. We retrospectively identified patients with HER2-positive MBC who received T-DM1 between April 1, 2014, and December 31, 2018, at the National Cancer Center Hospital, and focused on the population that received another line of therapy following T-DM1 discontinuation. Thirty patients were available for the outcome analysis. Median progression-free survival (PFS) of the first subsequent therapy was 6.0 months [95% confidence interval (95% CI) 4.1–6.4], whereas the median overall survival (OS) from the first subsequent therapy was 20.6 months (95% CI 13.5 months to not reached). We divided the patients into 2 groups according to their PFS with T-DM1 treatment and compared their PFS with the subsequent therapy. The results revealed a significant difference in the median PFS with the first subsequent treatment between patients with the PFS of less than and more than 3 months [5.1 (95% CI 1.7–6.2) vs 6.2 (95% CI 4.0–11.3) months, P = .03]. This is the first study to evaluate the survival outcomes of post-T-DM1 therapy in Japanese patients with HER2-positive MBC. A short PFS with T-DM1 might affect the PFS with a treatment after T-DM1.