Introduction: There is substantial evidence for the oncogenic effects of fibroblast growth factor receptor 1 (FGFR1) in many types of cancer, including lung cancer, but the role of this receptor has not been addressed specifically in lung adenocarcinoma. Methods:We performed FGFR1 and EGFR overexpression and co-overexpression assays in adenocarcinoma and in inmortalized lung cell lines, and we also carried out surrogate and interaction assays. We performed monotherapy and combination EGFR/FGFR inhibitor sensitivity assays in vitro and in vivo in cell line-and patientderived xenografts. We determined FGFR1 mRNA expression in a cohort of patients with anti-EGFR therapy-treated adenocarcinoma. Results:We have reported a cooperative interaction between FGFR1 and EGFR in this context, resulting in increased EGFR activation and oncogenic signaling. We have provided in vitro and in vivo evidence indicating that FGFR1 expression increases tumorigenicity in cells with high EGFR activation in EGFR-mutated and EGFR wild-type models. At the clinical level, we have shown that high FGFR1 expression levels predict higher resistance to erlotinib or gefitinib in a cohort of patients with tyrosine kinase inhibitor-treated EGFR-mutated and EGFR wild-type lung adenocarcinoma. Dual EGFR and FGFR inhibition in FGFR1-overexpressing, EGFR-activated models shows synergistic effects on tumor growth in vitro and in cell line-and patient-derived xenografts, suggesting that patients with tumors bearing these characteristics may benefit from combined EGFR/FGFR inhibition. Conclusion:These results support the extended the use of EGFR inhibitors beyond monotherapy in the EGFR-mutated adenocarcinoma setting in combination with FGFR inhibitors for selected patients with increased FGFR1 overexpression and EGFR activation.

The FGFR4-388Arg variant has been related to poor prognosis in several types of cancer, including lung cancer. The mechanism underlying this association has not been addressed in detail in patients with this pathology. Here, we report that this FGFR4 variant induces MAPK and STAT3 activation and causes pro-oncogenic effects in NSCLC in vitro and in vivo. This variant induces the expression of EMT-related genes, such as N-cadherin, vimentin, Snail1 and Twist1. Indeed, the induction of N-cadherin protein expression by this variant is essential for its pro-tumorigenic role. The presence of the FGFR4-388Arg variant correlates with higher N-cadherin expression levels in clinical NSCLC samples and with poorer outcome in patients with FGFR expression. These results support the prognostic role of this FGFR variant in lung cancer and show that these effects may be mediated by the induction of N-cadherin expression and an EMT phenotype.

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