They generally result from the recruitment and activation of different cell types, such as resident fibroblasts, vascular smooth muscle cells, and tumor-infiltrating mesenchymal stem cells, and are characterized by the expression of specific molecular markers, such as α-smooth muscle actin (α-SMA), fibroblast activating protein (FAP), and fibroblast-specific protein-1 (FSP-1); their induction is highly dependent on transforming growth factor-β (TGF-β) [13]. The gene discussed is S100A4; the disease is neoplasm.