According to Valtorta and colleagues, HER2 positivity is defined as 3+ IHC score (intense expression) in more than 50% of tumor cells or 3+ IHC score in 10–50% of the tumor cells and further FISH confirmation by HER2: CEP17 (chromosome enumeration probe) ratio ≥2 in more than 50% of tumor cells or 2+ IHC score (moderate expression) in more than 50% of tumor cells associated with a FISH positive evaluation. This evidence concerns the gene ERBB2 and neoplasm.