ERBB2 and breast cancer: Among patients with TNBC, basal-like breast cancer was the most common subtype in both HER2-low and HER2-IHC 0 breast cancer, but HER2-low breast cancer was characterized by a higher proportion of HER2-enriched subtypes compared with HER2-IHC 0 breast cancer (13.7% vs. 1.6%).