EGFR and neoplasm: Genetic analyses such as mutation and gene expression analysis of isolated tumor cells in spike experiments showed that KRAS mutation of spiked tumor cells was reproducibly detected at a single cell level, whereas gene expression at a relatively low level such as EGFR without gene amplification was difficult to detect quantitatively at a single cell level, indicating lower reproducibility of single cell gene expression analysis than single cell mutation analysis except for HER2 expression in the HER2 gene-amplified cells [39], [40].