Consistent with these clinical observations, we have performed two different analysis methods (i.e., FACS and IHC) in untreated CRC tumor tissues, both have shown that untreated CRC tumor tissues contain CEA+ and CEA−/lo cells, and importantly, the abundance of CEA−/lo CRC cells is enriched in poorly differentiated tumors or higher grade tumor areas. Here, CEACAM5 is linked to neoplasm.