KLF4 and breast cancer: The tumorsphere formation ability was increased, and aldehyde dehydrogenase and the levels of a panel of established CSC markers, krüppel-like factor 4 (KLF4), nanog homeobox (NANOG), SRY-box transcription factor 9 (SOX9), and ALDH1A1 were all elevated in breast cancer cells co-cultured with CCL20-moducated PMN-MDSCs.