Résumé : Introduction: Non-small cell lung cancers (NSCLC) are the most common lung cancers, withpeak incidence at 65 years of age. These cancers rarely occur before the age of 40. Methods: Based on an illustrative clinical case, a systematic review of the literature was conducted to study the epidemiological, clinical, histological, and biological characteristics of NSCLC in adults under 40 years of age. Two equations were developed to search for articles on Medline and Scopus. Results: Sixty-five articles were included in the review; 1.7% of patients were under 40 years old, 50.7% were women, 66.7% presented adenocarcinoma, 51.9% were diagnosed at stage IV, 75% were non-smokers, 39.9% were exposed to other toxins, 33% had an EGFR mutation, 6.6% had a KRAS mutation, 25% had an ALK translocation, 73.7% were symptomatic, and over 75% had PS < 2. Conclusion: NSCLC in patients under 40 years of age presents characteristics different from those in older patients. Various factors are implicated, one example being lower exposure to tobacco, and they can influence the distribution of histological subtypes and the frequency of mutations.