ERBB2 and neoplasm: It should be noted that intratumoral HER2 IHC heterogeneity (i.e., uneven distribution of HER2 expression or different intensities of HER2 staining in tumor cells) is more frequent in the HER2-low (2 + or 1 + IHC score) samples (Seol et al., 2012; Wu et al., 2023a).