EGFR and non-small cell lung carcinoma: Finally, to investigate potential clinical correlates of these findings, we first performed immunohistochemical (IHC) staining to quantify p-ATM S1981 expression in matched tumor samples taken from patients with EGFR mutant NSCLC before (treatment naïve, TN) and during (progressive disease, PD) treatment with the EGFR inhibitor erlotinib.