Utility of Liquid Biopsy by Improved PNA-LNA PCR Clamp Method for Detecting EGFR Mutation at Initial Diagnosis of Non–Small-Cell Lung Cancer: Observational Study of 190 Consecutive Cases in Clinical Practice

We reviewed 190 consecutive unselected patients who underwent liquid biopsy for detecting an EGFR mutation. The results indicated that not all patients should be candidates for liquid biopsy at initial diagnosis, while some patients gain benefit from initial liquid biopsy in clinical practice. These real-world data supply useful information in choosing patients appropriate for liquid biopsy. The clinical benefit of liquid biopsy for unselected patients at initial diagnosis has thus far been unclear. We aimed to evaluate the utility of liquid biopsy at initial diagnosis, as well as the efficacy of epidermal growth factor receptor–tyrosine kinase inhibitor (EGFR-TKI) based on liquid biopsy results in clinical practice, using the improved peptide nucleic acid–locked nucleic acid (PNA-LNA) PCR clamp method. We routinely performed liquid biopsy using the improved PNA-LNA PCR clamp method for all patients diagnosed with non–small-cell lung cancer (NSCLC) between June 2015 and October 2016. We retrospectively evaluated the reliability of liquid biopsy based either on clinical stage or between sensitizing EGFR mutation and T790M mutation, and the clinical benefit of EGFR-TKI based on the liquid biopsy results in practice. A total of 244 patients underwent liquid biopsies, with 168 patients tested at diagnosis and 22 tested for T790M after pretreatment of EGFR-TKI. For detecting a sensitizing EGFR mutation, the sensitivity, specificity, positive predictive value, and negative predictive value were 72.7%, 100%, 100%, and 93.7% in the group with advanced-stage NSCLC and 0, 100%, not evaluable, and 70.5% in the group with early-stage NSCLC. The positive predictive value and negative predictive value for T790M were 33.3% and 55.6%, respectively. Fourteen patients in the liquid-positive group and 16 patients in the tissue-positive group received EGFR-TKI. The objective response rates of first- and second-generation EGFR-TKI for the liquid-positive and tissue-positive groups were 90.0% and 90.9%, respectively. There was no significant difference in median progression-free survival between the liquid-positive and tissue-positive groups (P = .839). Patients with early-stage NSCLC should not be candidates for this liquid biopsy method. We recommend tissue biopsy as the preferred initial method of molecular analysis, with the exception of patients who are T790M positive or patients who are unable to tolerate invasive biopsy. [Display omitted]