PTPRC and colorectal carcinoma: CTCs were traditionally defined as EpCAM-isolated intact cells showing positive staining for CK but negative staining for CD45.20 This conventional definition has inevitably ignored CD45 positive cells with cancer cell characteristics.2,9 To determine whether CD45+ CTCs exist in the circulation of cancer patients, we first isolated CTCs from the peripheral blood of colorectal cancer (CRC) patients using Cellab Thomas I CTCs processing workstation (Fig. 1a).