Controlled activation of epidermal growth factor receptor (EGFR) is sys-tematically guaranteed at the molecular level; however, aberrant activation of EGFR is frequently found in cancer. Transcription induced by EGFR activation often involves the coordinated expression of genes that positively and negatively regulate the original signaling pathway; therefore, altera-tions in EGFR kinase activity may reflect changes in gene expression asso-ciated with the pathway.