Next‐generation sequencing (NGS) and digital PCR technologies allow analysis of the mutational profile of circulating cell‐free DNA (cfDNA) in individuals with advanced lung cancer. We have now evaluated the feasibility of cfDNA sequencing for mutation detection in patients with non‐small cell lung cancer at earlier stages. A total of 150 matched tumor and serum samples were collected from non‐small cell lung cancer patients at stages IA–IIIA. Amplicon sequencing with DNA extracted from tumor tissue detected frequent mutations in EGFR (37% of patients), TP53 (39%), and KRAS (10%), consistent with previous findings. In contrast, NGS of cfDNA identified only EGFR,TP53, and PIK3CA mutations in three, five, and one patient, respectively, even though adequate amounts of cfDNA were extracted (median of 4936 copies/mL serum). Next‐generation sequencing showed a high accuracy (98.8%) compared with droplet digital PCR for cfDNA mutation detection, suggesting that the low frequency of mutations in cfDNA was not due to a low assay sensitivity. Whereas the yield of cfDNA did not differ among tumor stages, the cfDNA mutations were detected in seven patients at stages IIA–IIIA and at T2b or T3. Tumor volume was significantly higher in the cfDNA mutation‐positive patients than in the negative patients at stages T2b–T4 (159.1 ± 58.0 vs. 52.5 ± 9.9 cm3, P = 0.014). Our results thus suggest that tumor volume is a determinant of the feasibility of mutation detection with cfDNA as the analyte.

Fibroblast growth factor receptor (FGFR) gene alterations are relatively frequent in lung squamous cell carcinoma (LSCC) and are a potential targets for therapy with FGFR inhibitors. However, little is known regarding the clinicopathologic features associated with FGFR alterations. The angiokinase inhibitor nintedanib has shown promising activity in clinical trials for non‐small cell lung cancer. We have now applied next‐generation sequencing (NGS) to characterize FGFR alterations in LSCC patients as well as examined the antitumor activity of nintedanib in LSCC cell lines positive for FGFR1 copy number gain (CNG). The effects of nintedanib on the proliferation of and FGFR signaling in LSCC cell lines were examined in vitro, and its effects on tumor formation were examined in vivo. A total of 75 clinical LSCC specimens were screened for FGFR alterations by NGS. Nintedanib inhibited the proliferation of FGFR1 CNG‐positive LSCC cell lines in association with attenuation of the FGFR1–ERK signaling pathway in vitro and in vivo. FGFR1 CNG (10.7%), FGFR1 mutation (2.7%), FGFR2 mutation (2.7%), FGFR4 mutation (5.3%), and FGFR3 fusion (1.3%) were detected in LSCC specimens by NGS. Clinicopathologic features did not differ between LSCC patients positive or negative for FGFR alterations. However, among the 36 patients with disease recurrence after surgery, prognosis was significantly worse for those harboring FGFR alterations. Screening for FGFR alterations by NGS warrants further study as a means to identify patients with LSCC recurrence after surgery who might benefit from nintedanib therapy.