GCNT1 and carcinoma: The direct demonstration of C2-O-sLex on the cell surface is essential because other enzymes such as the glycosyltransferase ST3 beta-galactoside alpha-2,3-sialyltransferase 1 can compete with C2GnT1 in carcinoma cells and inhibit the conversion of core 1 O-glycans to core 2 [38].