ERBB2 and neoplasm: However, a very high level of heterogeneity in HER2 expression isobserved (14–79% by IHC and 23–54% by IHC + FISH).Furthermore, the HER2 status of a tumor can change during anti-HER2 therapy,causing difficulties in assessing the effectiveness of the ongoing treatment,as performing multiple biopsies is associated with risks of complications andis not always an option[62, 63].