ABCG2 and neoplasm: In addition to the well-recognized role of P-glycoprotein (P-gp), which is encoded by MDR1 (ABCB1) gene, breast cancer resistance protein (BCRP), which is encoded by ABCG2 gene or mitoxantrone-resistance (MXR) gene and located on chromosome 7q22 [7], [8], also plays an increasingly important role in producing MDR tumor cells [9].