LIquid Biopsy to prEdict Responses To First-line immunotherapY in Metastatic Non-small Cell LUNG Cancer. LIBERTY LUNG

"* At pre-screening NGS analysis on tumor tissue (slides). Only patients with at least 1 mutation at NGS on the tumor tissue will ultimately be enrolled in the main study, to have the possibility to follow the mutation using ctDNA.~* Main study will be initiated after results of the NGS and before initiation of pembrolizumab. Blood specimens will be taken with EDTA tubes or streck tubes at the time of puncture for pembrolizumab infusion at baseline before starting treatment, at 3 weeks, 6 weeks and then every 6 weeks (30 ml at Baseline then 20 ml of blood). Blood immunomonitoring will be done before starting the treatment, at 6 weeks and at 18 Week. An additional measurement will be performed if treatment is stopped before the end of the study (18 ml of blood).~* Optional blood samples will be realized to analyse the degree of activity of the plasmatic lymphocytes before starting the treatment and at 6 weeks and (18 ml of blood)."