It has distinct subsets of functional fibroblasts differentiated from resting fibroblasts, such as tumor-restraining (F1), tumor-promoting (F2), secretory (F3), and ECM-remodelling (F4) subtypes detected and identified by various means based on the expression of a limited set of cell surface markers, such as α-SMA, vimentin, FAP, PDPN, PDGFRα/β, FSP1, DDR2, and S100A4 [36–39]. The gene discussed is PDPN; the disease is neoplasm.