PTPRK and cancer: PTPRK is also a transforming growth factor β1 (TGFβ1) target gene in mammary epithelial cells (Wang et al., 2005), synoviocytes (Stanford et al., 2016) and keratinocytes (Xu et al., 2015), and has been implicated as a tumour suppressor in several cancer types, particularly colorectal cancer (Chen et al., 2015; March et al., 2011; Starr et al., 2009).