Toll-Like Receptors (TLR) recognize pathogen molecules and danger-associated signals which stimulate inflammatory processes. TLR have been studied mainly in antigen-presenting cells where they exert important immune regulatory functions, but they are also expressed by epithelial tumor cells where they have been implicated in tumor progression. In this study, we demonstrate that the injection of TLR7 agonist in NOD/SCID mice, in C57BL/6 wild-type and TLR7 deficient mice grafted with lung adenocarcinoma tumor cells leads to increased tumor progression and chemotherapeutic resistance. In non-small cell lung cancer patients, expression analyses revealed that high TLR7 expression was strongly associated with resistance to neo-adjuvant chemotherapy and poor clinical outcomes. Our findings delineate a crucial role for TLR7 in lung cancer physiopathology.