Recruitment of MSC to the tumor environment leads to enhanced proliferation of OS stem cells. The presence of CSC, in turn, leads to a consistent secretion of TGFβ1 that activates a stromal autocrine loop that might be responsible for the activation of NF-kB genes and IL-6 secretion by MSC. Indeed, neutralization of TGFβ1 reduces the amount of secreted IL-6. Pro-tumorigenic effects of MSC, via IL-6, including induction of HOS-CSC migration and sphere growth, can be counteracted also by IL-6 neutralizing antibody. The presence of MSC is also responsible for increased expression of adhesion molecules involved in intra- or extra-vasation and the expression of MET can be counteracted by IL-6 neutralization.