Although ErbB3 and ErbB4 have previously been reported to be ER-suppressed, antihormone-induced genes in MCF-7 cells [22], we believe that the present article is the first to report acute induction of these receptors at the protein level by antihormonal therapy in a panel of HER2 low-expressing and overexpressing ER-positive breast cancer cell lines. This evidence concerns the gene ERBB4 and breast carcinoma.