Estrogens serve as ligands for two nuclear-receptor isoforms, estrogen receptor alpha (ERα) and estrogen-receptor beta (ERβ), and ERα has been implicated in oncogenic functions and the increased proliferation of cancer cells, while ERβ has tumor-suppressor functions because its loss leads to hyperplasia of the prostate and the initiation of PCa [81,82,83,84]. Here, ESR1 is linked to cancer.