Immunotherapy is probably, since the development of therapies targeting EGFR mutations or ALK rearrangement, the most attractive therapeutic perspective in the management of metastatic lung cancer. Among the compounds tested, the inhibitors of the immune checkpoint PROGRAMME DEATH 1 / PROGRAMME DEATH LIGAND 1 (PD-1/PD-L1) have been tested in numerous clinical trials with recently published positive results leading to the approval of one drug in the USA and an expanded access program for two drugs in France. PROGRAMME DEATH LIGAND 1 (PD-L1) expression by tumor cells is strongly associated with the response to such molecules so that the participation in various clinical trials is currently reserved for patients expressing this biomarker and therefore justifies a new invasive biopsy (bronchoscopic or CT-guided) representing a considerable drag on the access to these treatments. Circulating tumor cells (CTCs) isolated by Isolation by Size of Tumor Cells (ISET) offer a direct and non-invasive access to the tumor. It has already been demonstrated that molecular characterization (EGFR, ALK) on these blood samples is possible. We propose to demonstrate the feasibility of the analysis PDL-1 expression in these cells by immunocytochemistry.

Myeloid-Derived Suppressor Cells (MDSCs) are immature myeloid cells that inhibit T cell functions and thus promote tumor growth. These cells frequently express PD-L1. We propose to test whether MDSCs level and its evolution during treatment with PD1 inhibitor is correlated to the response to these drugs.

The main objective of this study is to demonstrate the feasibility of the analysis of PD-L1 expression on CTC

Inclusion Criteria:

• Stage IV non-small cell lung cancer patient prior to start immunotherapy treatment
• Patients with World Health Organization (WHO) performance status 0-3
• Patients who were informed and had non opposition form signed by investigator
• Patients with healthcare insurance system affiliation

Exclusion Criteria:

• Prior malignancy within 5 years of study entry
• Refusal to participate
• Patient under legal protection

Stage IV non small lung cancer patients