It is well known that tumor cells exposed to chemotherapeutic agents over time may develop, both in vivo and in vitro, a multidrug resistant (MDR) phenotype, which is generally associated with over-expression of P-glycoprotein (P-gp), the family of multidrug resistance-associated proteins (MRPs) and lung resistance-related protein (LRP)41. The gene discussed is PGP; the disease is neoplasm.