We identified a large group of patients with luminal — i.e., ER+HER2– — breast cancer, who by CIT256 were assigned a nonluminal intrinsic subtype; these patients had a significantly impaired overall survival (HR, 2.08; 95% CI, 1.51–2.86) compared with patients with a dual (IHC and CIT256) luminal subtype. Here, ERBB2 is linked to breast cancer.