ABCG2 and breast cancer: In contrast to genetic variability, the expression levels of ABC transporters are more accurate in predicting chemotherapy resistance and can serve as robust biomarkers for remission and survival across various cancers, including hematological cancers, as well as various solid tumors, such as melanoma, colorectal cancer, ovarian cancer, Ewing sarcoma and breast cancer (Pasello et al. 2019; Fletcher et al. 2010).