ABCB1 and neoplasm: Zhang et al (2008) have recently identified a sub-population of CD44+CD117+ cells (ovarian cancer-initiating cells) from primary ovarian cancer tissues that are fully capable of a serial propagation of their original tumour phenotype in animals, suggesting that CD44 is involved in EOC progression. It was reported that hyaluronan–CD44 interactions regulate the expression of drug transporters, including P-glycoprotein (MDR1) and MRP2 (Misra et al, 2005).