Role of circulating tumor DNA in the detection of sensitizing and resistance to epidermal growth factor receptor mutations in metastatic lung adenocarcinoma

Purpose: The EGFR (Epidermal Growth Factor Receptor) mutations may predict sensitivity and resistance to EGFR-TKIs (Tyrosine Kinases Inhibitors) in metastatic lung adenocarcinoma. The detection of these mutations is usually performed on tumor tissue samples. However, when a biopsy is not feasible or the amount of tissue is limited, circulating tumor DNA (ctDNA) may represent an alternative source for genotyping the tumor. Methods: In the first phase of the study, the liquid biopsy was performed in newly diagnosed metastatic lung adenocarcinoma patients with and without EGFR mutations to evaluate the concordance between EGFR mutational analysis on ctDNA by real time PCR and on tissue. In the second phase it was performed in EGFR positive patients progressing after first or second generation TKIs in order to detect the T790M mutation. Results: In the first phase, a 100% concordance between EGFR on ctDNA and tissue was revealed, leading to validation of the test. In the second phase, 44.8% of patients showed T790M positive result at liquid biopsy. Considering the rebiopsies performed in 31% of the cases, the overall positivity rate of T790M was 58.6%. Sensitivity and specificity were 76% and 75%, respectively. The median time to development of T790M mutation from the start of first line EGFR TKI was 244 days. Conclusions: : Our experience confirms that liquid biopsy is a valid method to detect sensitizing and resistant EGFR mutations in patients with metastatic lung adenocarcinoma. Nevertheless, in the presence of negative ctDNA analysis, a rebiopsy should be performed whenever possible to confirm this result.