Quantitative Immuno cytochemical Assays of P-glycoprotein in Breast Carcinomas: Correlation to Messenger RNA Expression and to Immunohistochemical Prognostic Indicators

Background: Chemotherapy failure that is due to cellular drug resistance remains a major problem in most cancer patients. One type of drug resistance that has been characterized is the multidrug resistance phenomenon, which demonstrates a reduced ability of cancer cells to accumulate drugs as a result of the effects of an energy-dependent unidirectional drug efflux pump with a broad substrate specificity. This drug pump is composed of a 170-kd transmembrane glycoprotein referred to as the P-glycoprotein (P-gp) that uses energy in the form of adenosine triphosphate to transport drugs through a channel formed by transmembrane segments