For other cancers, there is evidence that—based on heterogeneous genetic changes with already established prognostic influence—special treatment strategies might be proposed.40,41,53 In breast cancer, the presence of between 5 and 50% of cells with HER2/CEP17 ratios of >2.20 has been suggested as hetHER2 amplification because of the observed EFS decrease.54 However, recent studies have shown some contradictory results concerning treatment responses in heterogeneously amplified HER2 breast cancer.55 Here, ERBB2 is linked to breast carcinoma.