CD44 and breast cancer: Furthermore, CD44-/CD24-triple negative breast cancer (TNBC) cells spontaneously converted into CD44+/CD24-cancer stem cells (CSCs) with properties similar to CD44+/CD24-CSCs from primary human breast cancer cells and parental TNBC cells in terms of stemness marker expression, self-renewal, differentiation, tumorigenicity, and lung metastasis in vitro and in NOD/SCID mice.