Many extrinsic and intrinsic factors are involved in therapeutic resistance: the presence of cancer stem cells in tumors, changes in the tumor microenvironment, tumor immune evasion, overexpression of ABC or efflux transporters that reduce intracellular drug concentrations, oncogenic signaling, and metabolic alterations together with genomic instability are all involved in the development of resistance to monotherapy. This evidence concerns the gene ABCB6 and neoplasm.