Of the BMP/TGF‐β receptor inhibitors evaluated in vitro, LDN‐212854 was the most potent to suppress BMP9‐ID1 signaling and CSC properties, and thus, we selected LDN‐212854 as the inhibitor for assessing the antitumor effect on HCC xenografts. The gene discussed is GDF2; the disease is hepatocellular carcinoma.