Tyrosine kinase inhibitors in HER2‐positive metastatic breast cancer with trastuzumab emtansine resistance: insights from a multicenter retrospective real‐world study

The use of trastuzumab emtansine (T‐DM1) has revealed significant efficacy in HER2‐positive metastatic breast cancer (MBC). However, optimal therapeutic strategies following T‐DM1 failure remain a subject of debate in clinical practice. In this multicenter, retrospective, real‐world study, we sought to examine the effectiveness and safety of tyrosine kinase inhibitors (TKIs) as a therapeutic strategy in HER2‐positive MBC who developed T‐DM1 resistance. Between September 2018 and December 2022, 66 patients were enrolled. The median progression‐free survival of TKIs‐based therapy was 10.1 months (95% CI, 4.7–15.6). Objective response rate and clinical benefit rate were 18.2 and 66.7%, respectively. TKIs‐based therapy demonstrated better effectiveness in patients who had previously derived benefit from T‐DM1 and featured acquired resistance to trastuzumab. The most common adverse events were diarrhea (36, 54.5%), hand‐foot syndrome (31, 47.0%), and leucopenia (30, 45.5%). In conclusion, TKIs‐based therapy showed promising effectiveness and safety in HER2‐positive MBC patients after T‐DM1 failure.