In particular, neosynthesis and over-modification of simple mucin-type O-glycans, such as the Tn antigen (GalNAc-Ser/Thr), Sialyl Tn antigen (Siaα2-6GalNAc-Ser/Thr; STn), and T antigen (Galβ1-3GalNAc-Ser/Thr), play important roles in tumor progression and malignancy in various cancers, and are associated with changes in protein conformation and signaling (24–30). Here, MUC5AC is linked to cancer.