Non-small-cell lung cancer (NSCLC) ranks among the neoplasms with the worst prognoses and the highest mortality rates. Several factors, mainly clinical, are known that provide a predictive value on the course of the disease. In the era in which we live, the molecular basis of cancer is studied in depth and several molecular markers have been described that could play a prognostic role or that could predict the probability of responding to the different treatments used. Moreover, some mechanisms have been proposed that could explain primary or acquired resistance to treatment with chemotherapy and to targeted therapies. Knowing all these pathways is very important, as it allows the development of selective therapeutic strategies that minimise toxicity and optimise treatment effectiveness. However, the data obtained yield results that are at times contradictory, prospective studies with biomarkers thus being necessary so that their role can be established with the necessary evidence.