CD44, as a marker for cancer stem cells, was downregulated in BCCs co-cultured with MSCs; this led to a decrease in proliferation and an increase in chemo-resistance (represented by reduced killing by docetaxel) [51], which is concordant as rapidly proliferating cells are usually more susceptible to chemotherapy, whereas there is also evidence suggesting the promotion of MSCs on breast cancer stem cell phenotypes and tumor progression [59,60]. This evidence concerns the gene CD44 and cancer.