ID1 and neoplasm: The prevailing view is that ID1 is downregulated by TGF-β in non-tumorigenic human epithelial lines, but upregulated by TGF-β in established tumor cell lines, as we have observed here in MDA-MB-231 and BT-549s, and also in patient-derived tumor cells (Anido et al., 2010; Padua et al., 2008; Lasorella et al., 2014).