ERBB2 and neoplasm: (iv) The same effect might be caused by subclonality of the tumor cells, where some tumor cells are HER2-amplified, but the majority of tumor cells is not amplified for HER2. (v) Inter-block tumor inhomogeneity may contribute to the discordance as NGS and IHC/SISH were not conducted using consecutive sections because we used frozen tissues for sequencing but FFPE tissues for HER2 status determination.