In this study, multi-factorial drug-resistant cancer cell lines such as leukemia CEM/ADR5000 cells over-expressing P-glycoprotein, breast adenocarcinoma MDA-MB-231-BCRP clone 23 expressing BCRP, p53 knockout HCT116 (p53−/−) colon cancer cells and EGFR-transfected U87MG.ΔEGFR glioblastoma cells [4, 7, 12, 20–22, 28] were used to determine to assess the cytotoxicity the selected plant extracts. The gene discussed is ABCG2; the disease is breast adenocarcinoma.