ERBB2 and breast carcinoma: For this reason, we examined the levels of this kinase in MDA-MB-231 (claudin low), SKBR3 (HER2+) and MCF7 (luminal) breast cancer cell lines and found that as expected, NIK is highly expressed in MDA-MB-231 cells and barely detectable in MCF7 cells (Supplementary Fig. S2).