ABCC4 and neoplasm: Tumors derived from MDA-MB-231 shVec/Luc cells had higher ABCC4 mRNA expression compared to tumors derived from MDA-MB-231 shMRP4-C/Luc or MDA-MB-231 shMRP4-D/Luc MRP4 knockdown clones indicating that the tumor MRP4 phenotype at the end of the observation period reflected the phenotype of the initial implanted tumor cells.