We conducted a systematic review of repeat biopsy studies in patients with NSCLC who developed resistance to EGFR-TKIs, so as to determine if there was a difference in the incidence of the T790 M EGFR mutation between patients with deletions in exon 19 and point mutations in exon 21 (L858R). This evidence concerns the gene EGFR and non-small cell lung carcinoma.