ACTA1 and cancer: On the other hand, progenitor states lack α-SMA expression and are transformed to α-SMA-positive CAFs via cancer cell-derived growth factors such as transforming growth factor-β (TGF-β) (Orimo et al. 2005), platelet-derived growth factor (PDGF) and fibroblast growth factor-2 (FGF-2) (Elenbaas and Weinberg 2001), Wnt7a (Avgustinova et al. 2016), sonic hedgehog (Shh) (Bailey et al. 2008), and exosomes (Paggetti et al. 2015; Webber et al. 2015).