ERBB2 and neoplasm: Heterogeneous patterns further include clustered (regional) patterns, characterized by segregated populations of HER2-stained and non-stained tumor cells, mosaic (intermixed) patterns, where HER2-stained cells are intermixed with a non-stained tumor cell, and scattered patterns, where isolated HER2-stained cells are observed amidst a background of non-stained tumor cell population [9].