ERBB2 and breast cancer: 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