NEU4 and neoplasm: As both NEU3 and NEU4 have an affinity preference for cleaving α2–3 and α2–8 sialic acids over α2–6 sialylated structures, this suggests the existence of a dichotomy between sialyl-Lewis and α2–6 sialylated epitopes (generated by ST6GAL1 and ST6GALNAC1) promoting invasiveness and, in contrast, certain other α2–3 moieties, like sialyl-T, protecting against tumor spread to distal organs.