P4HB and breast cancer: Glycomic analysis have identified seven glycosylated proteins with O-linked β-D-N-acetylglucosamine (O-GlcNAc), an important post-translational modification involving reversible and highly dynamic covalent binding of β-N-GlcNAc to Ser/Thr residues in proteins (48), such as vimentin, keratin 7, enolase 2, pyruvate kinase isozyme M 2 (PKM2), protein disulfide isomerase (PDI) A6, TP, and voltage-dependent anion selective channel protein in breast cancer (31) (Table 1).