PGP and breast cancer: In a study on the effect of β-elemene on MCF-7/ADM (Adriamycin-resistant cells) breast cancer stem cells (BCSC), the expression of P-gp and BCRP in MCF-7/ADM cells was 77.78 ± 9.55% and 32.33 ± 5.12%, respectively, and the CD44+ CD24−/low cell rate was 64.79 ± 11.78%, which were significantly higher than in MCF-7/S cells (3.97 ± 1.51, 14.26 ± 2.51, 18.79 ± 3.28%, respectively).