Strikingly, we found that although PTPN2‐expressing central memory CD8+ HER‐2 CAR T cells modestly suppressed HER‐2‐E0771 mammary tumour growth, PTPN2‐deficient CD8+ HER‐2 CAR T cells eradicated tumours (Fig 4A). Here, PTPN2 is linked to breast cancer.