CMAS and cancer: Targeting aberrant sialylation in cancer using small molecule inhibitors is emerging as a promising therapeutic approach.14,15 Paulson and co-workers have previously developed a cell-permeable metabolic inhibitor of sialylation based on peracetylated 3-fluorosialic acid (P-SiaFNAc).16 Upon entering the cell, P-SiaFNAc is deacetylated by esterases and converted into the active nucleotide sugar CMP-SiaFNAc by the CMP-sialic acid synthetase (CMAS).