ERBB2 and neoplasm: The ASCO/CAP 2013 guidelines defined heterogeneity as findings of between 5 and 50% of total cells with HER2/CEN17 ratio >2.0 or >6 Her2 signals/cells (72), and the ASCO/CAP 2018 update such as the presence of any aggregated population of amplified cells comprising >10% of the tumor cells on the slide (4).