ABCG2 and leukemia: Its anti-cancer potential to reverse multi-drug resistance (MDR) has been shown in daunorubicin-resistant P388 leukemia cells (Gupta et al., 1991), adriamycin-resistant K562 leukemia cells (Kurosawa et al., 1996), human breast cancer resistance protein-expressing HEK cells resistant to topotecan (Gupta et al., 2007), P-glycoprotein (MDR1)-overexpressing, multidrug-resistant HeLa cells (Iida et al., 2001), bevacizumab-resistant gastrointestinal cancer (Hara et al., 2016) and metastatic castration-resistant prostate cancer (Antonarakis et al., 2013).