ABCA4 and cancer: In addition to the drug efflux pump (copper transporters, sole carrier transporters, and ATP-binding cassette transporters) that can expel drugs and reduce intracellular concentrations in cancer cells, there are other mechanisms, such as activation of DNA repair systems, inhibition of cell death, detoxification via glutathione, the emergence of cancer stem cells, the epithelial-mesenchymal transition (EMT), and epigenetic alterations16,17,19,20.