SLC31A1 and neoplasm: Remarkably, CTR-1 transports copper in the form of Cu(I) instead of copper(II) [76–78], thus, if the upregulation of CTR-1 indeed is responsible for the transport of copper to the hypoxic tumor sites, copper(II) must have been disassociated and reduced to Cu(I) in blood, before it is delivered to the tumor through the copper secretory pathway.