RARG and cholangiocarcinoma: Schug et al. (2008) showed overcoming RA resistance in breast cancer by diverting RA from PPARβ/δ to RAR mechanisms. Apart from RARβ, which is involved in the cell differentiation process, RARγ, in turn, plays a role in the progression of several cancers, such as cholangiocarcinoma, hepatocellular carcinoma, and esophageal cancer. However, knockdown of RARγ has been proven to show drug resistance reversal in the aforementioned cancers (Huang et al., 2017).