Additionally, using CAPP-Seq based ctDNA analysis, Chabon et al. recently found evidence for multiple resistance mechanisms in 46% of lung cancer patients following treatment with first-line EGFR TKIs [25], while prior tissue biopsy based studies have reported heterogeneity of resistance mechanisms in only 5%–15% of patients [20–22, 25]. This evidence concerns the gene EGFR and lung carcinoma.