However, it has been suggested that ABCG2 expression may be associated with a poor response to cancer chemotherapy and clinical drug resistance [6] associated with the efflux of drugs from cancer cells and multidrug resistance (MDR) to a variety of chemotherapeutic agents, small-molecule inhibitors like tyrosine kinase inhibitors (TKIs) or cyclin-dependent kinase 9 (CDK9) inhibitors [7]. Here, ABCG2 is linked to cancer.