ABCG2 and breast cancer: The present work has taken this into account and involves several models of MDR cancer cell lines such as the colon adenocarcinoma with p53 knockout phenotype, the leukemia cells with ATP-binding cassette (ABC)-transporter-overexpressing MDR-mediating-P-glycoprotein (P-gp; ABCB1/MDR1), the breast cancer bearing resistance protein (ABCG2/BCRP), and the transfectant glioblastoma multiforme harboring a mutation-activated EGFR gene (ΔEGFR).