HGF and breast neoplasm: Differences in the activity of NFs versus CAFs in breast tumors may result from alterations in molecular and/or cellular mechanisms that are responsible for the production and release by CAFs of a number of soluble factors such as fibroblast growth factors [13], transforming growth factor-β (TGF-β) [14], insulin-like growth factors [15], and hepatocyte growth factor (HGF) [12].