Importantly, we found that Ptpn2 deletion led to the effective eradication of HER‐2‐E0771 mammary tumours (Fig 8F) and this was accompanied by the increased infiltration of mCherry+ HER‐2 CAR T cells into HER‐2‐E0771 mammary tumours (Fig 8G) in vivo. Here, ERBB2 is linked to breast cancer.