No significant difference with IC50 values was found among breast cancer cells with low HER2-expressing cells MCF-7 and MDA-MB-231, and with high HER2-expressing cells MCF-7/HER2, SKBR3, MDA-MB-453 and BT-474 cells, demonstrating that the growth inhibitory effect of tunicamycin was not depended on HER2 expression levels. Here, ERBB2 is linked to breast cancer.