A potent and selective agonist of ERβ (Ki = 1.54 nM; EC50 = 3.61 nM); reduces the viability of patient-derived, ERβ+ primary GBM cells; reduces in vitro colony formation and induces apoptosis; induces G2/M arrest and sensitizes GBM cells to chemotherapeutic agents in vitro; reduces GBM progression in and increases survival of orthotopic and syngeneic GBM mouse models; induces dose-dependent reduction in prostate weight with no effect on levels of circulating testosterone or dihydrotestosterone in a rat model of BPH