Different cut-off values of ≤50 % in gastric and 5-50 % in breast cancers to define heterogeneous HER-2 amplification [39,40] have been applied and although EGFR copy number heterogeneity has been identified in non-small cell lung cancer [41] and colorectal cancer [42] no standardised classification system has been developed. The gene discussed is ERBB2; the disease is breast cancer.