ERBB2 and breast cancer: An ongoing phase 1 clinical trial is assessing the safety and tolerability of MSLN‐specific CAR T cells in patients with metastatic mesothelin‐expressing breast cancer (NCT02792114), while another study is investigating HER2‐specific CAR T cells to target the commonly found receptor human epidermal growth factor receptor 2 (HER2) in breast cancer along with other HER2 positive tumors (NCT02442297; NCT03696030).