The prognostic significance of epidermal growth factor receptor (EGFR) expression in lung cancer and, more importantly, its ability to predict response to anti-EGFR therapies, are currently subjects of active research. In a meta-analysis, EGFR overexpression confirmed a worse prognosis (HR 1.13) in eight studies using immunohistochemistry, although cutoff values were generally selected arbitrarily by investigators. Most applied clinical research on the EGFR has been focused on the overexpression of the receptor, whereas less research has addressed the potential role of other mechanisms of increased signaling or of nonmembrane-bound events. The emerging concept of EGFR signaling reveals a multilayered network that allows for horizontal interactions and permits multiple combinatorial responses that may explain the specificity of cellular outcomes to receptor activation. New technologies such as nucleotide arrays and proteomics will help to elucidate the issue by providing information on how EGFR signaling may affect the expression of genes and proteins in cancer cells.