ABCB1 and neoplasm: In this light, the overexpression of ATP binding cassette (ABC) transporters - such as P-glycoprotein (Pgp/ABCB1), multidrug resistance related proteins (MRPs/ABCCs) and breast cancer resistance protein (BCRP/ABCG2) - limits the intracellular retention and cytotoxicity of different chemotherapy drugs, conferring to tumor cells a multiple and cross-resistant phenotype known as multidrug resistance (MDR) [4].