ERBB2 and neoplasm: HER2 ITH may present in three distinct patterns based on the geographic (spatial) distribution of heterogeneity: (1) clustered (regional) type, defined as two distinct areas with different HER2 gene amplified tumor cell populations; (2) mosaic (intermixed) type, defined as diffuse intermingling of cells with different HER2 gene amplification status; (3) scattered type, defined as isolated HER2 amplified tumor cells in a predominantly non-amplified tumor [19,32].