ABCB1 and neoplasm: Although there are many mechanisms of resistance to drugs, like changes in mitochondria, induced DNA-repair, oncogenes or tumor suppressor genes, among others, as indicated previously, a classical one is comprised of transporter pumps (e.g., P-glycoproteins), that act by extruding xenobiotics from the cell in an ATP-dependent manner; such glycoproteins are overexpressed in a number of tumors.