ABCB1 and neoplasm: The resistance of tumor cells to chemotherapy can be a result of various processes: from active ATP-dependent transport of cytotoxic agents out of the cells executed by P-glycoprotein, the member of subfamily B of ABC-transporters [6, 7], to disorders in the apoptosis, mutations or downregulation of p53 gene, impairing its proapoptotic function, and/or overexpression of bcl-2 gene causing insensitivity of cells to proapoptotic stimuli [8–10].