SMAD3 and hepatocellular carcinoma: For example, a gene regulated by TGF-β only in MDA-MB-231 BTICs (MDA-unique gene) can be: (1) uniquely bound by SMAD3 in MDA-MB-231 (binding mode 1), (2) uniquely bound by SMAD3 in HCC-1954 (binding mode 2), (3) commonly bound by SMAD3 in both cell types (binding mode 3), and (4) not bound by SMAD3 in either cell type (binding mode 4).