However, on one hand the level of total EGFR protein expression is closely associated with poor prognosis of many types of cancers including those cancers resistant to anti-EGFR agents (31, 32, 34, 38, 39, 80, 156–159) and gene copy number of EGFR is currently one of the most reliable predictors for sensitivity to anti-EGFR therapeutics; on the other hand, the level of phosphorylated EGFR is not a reliable predictor of NSCLC's sensitivity to TKIs and mutational status of EGFR is (89, 176, 177)—why? Here, EGFR is linked to cancer.