Here, we demonstrate for the first time that Tel reduces ERα levels in six different ERα-expressing BC cell lines, acting as models of primary (i.e., MCF-7, T47D-1, and ZR-75-1 cells) and metastatic (i.e., BT-474, MDA-MB-361 and Y537S-ERα mutant-expressing MCF-7 [Y537S] cells) BC [3]. The gene discussed is ESR1; the disease is breast cancer.