To determine the generalizability of our previous conclusion, we introduced both wild-type (WT) ERβ and the functionally inactive tyrosine-to-phenylalanine (Y36F) mutant into ERα-positive breast cancer cells (MCF7), ovarian cancer cells (SKOV3), and glioblastoma cells (U87), which represent three cancer types where ERβ antitumor activity had been previously demonstrated [1, 4, 35]. The gene discussed is ESR2; the disease is breast cancer.