In the only studies in cancer, the expression of both DRD2 and DRD3 was found to be increased in breast cancer patients [15], and DRD2 and DRD3 were found to have the same expression levels in the cholangiocarcinoma cell lines Mz-chA-1 and SG231 [16]. This evidence concerns the gene DRD2 and cholangiocarcinoma.