STAT1 and breast cancer: The inducible overexpression of PTPN2 not only repressed IFNγ‐induced p‐STAT‐1 (Fig 7D) and Cxcl9/10 expression (Fig 7E), but most importantly also the recruitment of PTPN2‐deficient CAR T cells to HER‐2‐E0771 mammary tumours in vivo (Fig 7F–H).