HER2 expression was quantified in accordance with breast cancer clinical guidelines for intensity (0, 1+, 2+, 3+) and percent positive staining, and it was reported as an H-Score (intensity × percent positive staining) as well as HER2-low (IHC 1–2+ ≥ 10% of cancer cells) and HER2-ultralow (IHC 1+ at < 10% of cancer cells). Here, ERBB2 is linked to breast cancer.