Rapamycin was also cytotoxic in all three cell lines but did not exhibit a significant difference in cytotoxicity between the cell lines (p>0.05)(Figure 4B).The combination of rapamycin and cerulenin induced synergistic cytotoxicity in all three breast cancer cell lines, particularly in the ER+/HER2+ cells(MCF-7/HER2>SKBR3>MCF-7, p<0.05). Here, ESR1 is linked to breast cancer.