CD44 and breast cancer: To unravel the mechanisms that underpin CD44-promoted BC cell invasion, RNA samples were isolated from two cell models: (a) a tetracycline (Tet)-Off-regulated expression system of the CD44s in MCF-7 cells and; (b) as a complementary approach, the highly metastatic BC cells, MDA-MB-231, were cultured in the presence and absence of 50 μg/mL of HA.