Tissueanalysis should be carried out, as a negative ctDNA result does notalways imply that the matching tumor is mutation-negative.37−39 Deletion of Exon 19 (exon19del), which accounts for over 44% ofEGFR mutations, insertion of exon 21 (L858R), which accounts for roughly40% of EGFR mutations and G719S are the most common EGFR mutationsin nonsmall cell lung cancer (NSCLC) (Figure 4). Here, EGFR is linked to lung cancer.