Although several types of mechanisms are related to chemoresistance, such as changes in drug kinetics, amplification of drug targets or plasticity of the tumor microenvironment [11, 12], the one most commonly observed is the abnormal expression of energy-dependent efflux pumps encoded by the ABCB1 gene (P-glycoprotein 1, P-gp or MDR1) or other multidrug resistance-associated proteins (MRPs) [13, 14]. The gene discussed is ABCB1; the disease is neoplasm.