Notably, the bone marrow microenvironment is enriched in TGF-β, a cytokine that is well-known to induce EMT (Brown et al., 2004; Lee et al., 2008; Mani et al., 2008; Lenferink et al., 2010), and production of TGF-β by microenvironment stromal cells may be responsible for CD44+/CD24- breast cancer cells in bone (Abraham et al., 2005; Balic et al., 2006). Here, CD44 is linked to breast cancer.