CD44 and acute myeloid leukemia: The CSC concept was not novel, but it reinvigorated the field of cancer research following the isolation of CD44+CD24−/low CSC from primary breast cancer in 2003 by Al-Hajj et al. [15], several years after the establishment of CD34+CD38− CSC in acute myeloid leukemia (AML) in 1994 [16].