ERBB2 and breast cancer: In addition, the proportion of non-basal-like tumors in the HER2 IHC 2+ subgroup in our cohort was more than twice as high as that in the Western population9 (57.1% vs. 21.6%, P = 0.010, Fisher’s exact test) (Fig. 4b), which further indicated the interpatient heterogeneity among Chinese patients with HER2-low breast cancer.