A sequence-related subfamily of atp-binding cassette transporters that actively transport organic substrates. Although considered organic anion transporters, a subset of proteins in this family have also been shown to convey drug resistance to neutral organic drugs. Their cellular function may have clinical significance for CHEMOTHERAPY in that they transport a variety of antineoplastic agents. Overexpression of proteins in this class by neoplasms is considered a possible mechanism in the development of multidrug resistance (drug resistance, multiple). Although similar in function to p-glycoproteins, the proteins in this class share little sequence homology to the p-glycoprotein family of proteins.