PTPN2 and breast cancer: The PTPN2 protein has been shown to be lost in ER-negative breast cancer, more so in triple-negative breast cancers (TNBC) (Shields et al. 2013) and we have previously found that the protein is expressed at low levels in 53.3% of the tumours in a cohort of low-risk breast cancer patients (Karlsson et al. 2018).