ERBB2 and cancer: As a prelude to our cell culture analysis of gCISs, we assessed MET and RAS pathway activation as well as RhoA signaling in 59 breast cancer cell lines using the Cancer Cell Line Encyclopedia database (CCLE)73, classified by PAM50 into BasalA, BasalB/Claudin-low, HER2-enriched and luminal-like, as described74 (Fig. 4i).