The most frequently occurring secondary EGFR mutation in lung cancer is an exchange of a threonine for a methionine in position 790 (T790M) in exon 20; it is present in about 50 % of all cancers with acquired resistance to EGFR-TKIs (Engelman and Settleman 2008) but very rare in untreated NSCLC (Chmielecki et al. 2012). Here, EGFR is linked to lung cancer.