To determine whether matrine (Fig. 1A) is toxic to breast cancer cell lines, ER-positive MCF7 cells, HER2-positive BT-474 cells and the highly metastatic MDA-MB-231 cell line were treated with medium only (matrine, 0 mM) or matrine (1, 2 or 3 mM). The gene discussed is ERBB2; the disease is breast cancer.