A very limited number of studies estimated the impact of ABCB1 gene polymorphisms on Dox pharmacokinetics and pharmacodynamics [34,36,37,38,39,40], although the role of the ABCB1/MDR1 transporter in the regulation of intracellular concentration of anti-cancer agents and their therapeutic effects were reported [41,42]. This evidence concerns the gene ABCB1 and cancer.