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)