Moreover, overexpression of ERβ or its activation by means of agonistic ligands were reported to inhibit cell proliferation in different tumor cells, both classically related (breast, ovarian, and prostate cancer) [15–17] and unrelated (colon cancer, mesothelioma, cholangiocarcinoma, lymphoma) [18–21] to the reproductive system. This evidence concerns the gene ESR2 and cholangiocarcinoma.