Podocalyxin (PODXL), a highly sialylated type I transmembrane KS proteoglycan expressed on the luminal membrane of brain microvascular endothelial cells, is another illustrative example of the discriminative power of the charge status of its KS chains in normal tissues and tumours that is not picked up by antibodies to core protein epitopes. This evidence concerns the gene PODXL and neoplasm.