More specifically, highly tumourigenic BCSCs and their early progenitors endowed with a high self-renewal potential and which can express different stem cell-like markers such as CD44+, CD24−/low, epithelial-specific antigen (ESA+), CD133+, ALDH1high, Oct-3/4, Nanog, Kruppel-like factor (KLF-4) and/or CXCR4high have been detected and isolated from breast tumour specimens from patients and breast cancer cell lines [73–80, 88, 239]. Here, CD44 is linked to breast cancer.