Among the known mechanisms of breast cancer cells resistance to PTX, the most important are the active removal of the drug from the cell related to the increased activity of ATP-binding cassette (ABC) membrane transporters such as P-glycoprotein (P-gp; ABCB1), multidrug resistance-associated proteins (MRPs; ABCC), and breast cancer resistance proteins (BCRP; ABCG2) [3,4], enhanced drug detoxification by cytochrome P450, CYP3A4/5 and CYP2C8 enzymes [5,6], alterations in the molecular targets, microtubule and disorders of microtubule-associated proteins (MAPs) [7,8], or apoptosis [9,10,11]. The gene discussed is ABCG2; the disease is breast carcinoma.