SMAD4 and intrahepatic cholangiocarcinoma: In the study by Kang et al (29), the changes in both G1 to S cell cycle arrest and TGF-β/SMAD pathways were investigated by immunohistochemical staining for Rb, cyclin D1, p27, p16, p53, and SMAD4/Dpc4 in 42 intrahepatic cholangiocarcinomas (iCCA).