NFKB1 and breast carcinoma: Since NF-κB is activated in both HER2-positive and HER2-negative breast cancer cells in response to lapatinib treatment, we next examined the effect of p65 shRNA on the cell viability of SkBr3 and MDA-MB-231 cells and their lapatinib-resistant clones in both the presence and absence of lapatinib.