According to research by Haraguchi et al. [56], side population (SP) cells from human cancer cell lines of different gastrointestinal tracts overexpress ATP-binding cassette super-family G member 2 (ABCG2), ATP-binding cassette super-family G member 1 (ABCB1), and CEA cell adhesion molecule 6 (CEACAM6), which are implicated in chemoresistance and have several traits of CSCs [57]. This evidence concerns the gene CEACAM6 and cancer.