In the previous studies [6, 16], we have shown that RY10-4 is a potent anti-tumor compound against breast cancer cells, but the HER-2 overexpressing SKBR3 cell line proves less sensitive to RY10-4 than cell lines expressing lower levels of HER2, such as MDA-MB-231 and MCF-7 cells. This evidence concerns the gene ERBB2 and breast cancer.