This generation of breast cancer cells with both cancer stem cell and mesenchymal-like characteristics has again been shown to be dependent on an activation Ras/MAPK signaling, and the link between EMT and cancer cell “stemness” is supported by the fact that genes associated with angiogenesis, invasion and metastasis are overexpressed in stem cell- like CD44+/CD24− breast cancer cells; notably, after chemotherapy for breast cancer, residual tumor cells frequently display a stem cell-like phenotype and increased mammosphere formation efficiency [101,110,111]. This evidence concerns the gene CD44 and breast cancer.