The functional significance was established in OGT knockdown experiments in breast cancer cells, which resulted in diminished proliferation.38 When chronic lymphocytic leukemia cells were compared with normal lymphocytes, high intracellular UDP-GlcNAc and high OGT levels were found, accompanied by higher O-GlcNAcylation of c-Myc, p53 and AKT.39 Excessive STAT5 activation is oncogenic in several hematopoietic malignancies such as CML, MPN, ALL or AML. Here, STAT5A is linked to breast carcinoma.