STAT3 and breast carcinoma: To this end, when MCF7 breast cancer cells were treated with a STAT3 inhibitor or DMSO and radiated afterwards, we observed that the inactivation of STAT3 sharply attenuated the radiation-induced Notch2 (NICD2), Jagged1 and DLL4 mRNA expression and protein levels (Figure 4C and 4D).