Efek pemaparan Tamoksifen berulang pada sel punca kanker payudara CD24-/CD44+: kajian mengenai sensitivitas terapi melalui perubahan ekspresi estrogen reseptor alfa dan transporter efluks Multidrug Resistance-Associated Protein 2 (MRP2) = The Effects of repeated tamoxifen exposure to the breast cancer stem cells CD24-/CD44+: A study on sensitivity to therapy through changes in expression of estrogen receptor alpha and efflux transporter Multidrug Resistance-Associated Protein 2 (MRP2)