SLC17A5 and neoplasm: Tumor hypoxia induces the expression of NeuGcGM2 gangliosides in human cancer cells through the incorporation of the nonhuman sialic acid NeuGc, supporting the idea that the specific effect of hypoxia is to expedite sialic acid transport from the external medium, in relation with the increment of sialin expression (a sialic acid transport) [32].