To determine whether Z-endoxifen actions in ER+ breast cancer cells were affected by HER2 status, we also evaluated Z-endoxifen in cell lines that do not express HER2 (T47D), endogenously express HER2 (BT474), or stably over-express HER2 (MCF7-HER2–18). This evidence concerns the gene ERBB2 and breast carcinoma.