Comparing MDA-MB-231 and BT20 TNBC cells with MCF-7 estrogen-positive (ER+) breast cancer cells, Hirsch et al. found that the TNBC cells expressed > 3-fold higher levels of activated Cdc42 compared with MCF-7 cells, and this increase positively correlated with expression levels of EGFR. Here, ESR1 is linked to breast cancer.