PTPN2 and breast cancer: Few studies have been conducted on PTPN2 gene copy number in cancer, we have previously reported similar numbers; 15.8% (34/215) copy loss in tumours from the post-menopausal patients of the Stockholm breast cancer trial (Karlsson et al. 2015) and 17.8% (26/146) in the aforementioned low-risk cohort (Karlsson et al. 2018).