PGP and breast cancer: Quantification of BC formation according to MRP2 or P-gp immunolabelling indicated 17.7 ± 3.2 (MRP2 labelling) and 18.5 ± 2.7 (P-gp labelling) BC/100 nuclei for FSK-treated cells versus 3.9 ± 0.7 (MRP2 labelling) and 4.7 ± 1.6 (P-gp labelling) BC/100 nuclei for control cells (Fig. 2b).