ABCG2 and cancer: Development of chemoresistance involves a series of biological processes, such as the drug efflux caused by ‘drug pump’ (ABC transporter) on cell membrane, the abnormal drug metabolism in cancer cells, the dysregulation of cell‐cycle and DNA damage response, the hyper‐activation of pro‐survival signaling and anti‐apoptosis pathways, and the cancer stem cells (CSCs) enrichment..4, 5, 6