To determine whether these CD45+ cells originated from cancer, we sorted three populations of single cells from three colorectal cancer patients by FACS: (a) CD45+ Lineage-APC+ WBCs (Lineage contains CD3/14/16/19/20/56); (b) CD45+ Lineage-APC- EpCAM+ CTCs; (c) CD45− EpCAM+ CTCs. Here, PTPRC is linked to cancer.