HGF and cancer: We show that (i) the different PSC populations were heterogeneous, as they exhibited a wide range of variation with respect to their ability to stimulate the carcinoma cells and to secrete HGF, (ii) PSC-induced stimulation of cancer cells can be mediated by the HGF/Met signaling pathway, and (iii) in HGF-secreting PSCs, IL-1α and TGFβ can regulate the HGF levels as well as the HGF-mediated effects on the cancer cells.