The most frequent aberrant O-glycans expressed at the surface of cancer cells consist of Tn antigen (α1→Ser/Thr), T antigen (Galβ1→3GalNAcα1→Ser/Thr), Lewis a (Galβ1→3[Fucα1→4]GlcNAcβ1→R) and Lewis x (Galβ1→4[Fucα1→3]GlcNAcβ1→R) antigens, and an oncofetal glycotope, the Forssman pentasaccharide antigen (GalNAcα1→3GalNAcβ1→3Galα1→4Galβ1→4Glc) [1,2,3] (Figure 1). This evidence concerns the gene FUT4 and cancer.