FSTL3 and hepatocellular carcinoma: How HCC cells may escape from the proapoptotic and antiproliferative action of activin A? Activin A activity is known to be antagonised by several extracellular factors, including follistatin (Esch et al, 1987; Mashima et al, 1995), fstl3 (Tsuchida et al, 2000) and cripto (Gray et al, 2003).