Patient with histologically proven NSCLC in a metastatic stage, treatment naïve and eligible for first-line treatment with immune checkpoint inhibitor. Combination with chemotherapy is possible. Presence of a mutation after NGS analysis is required for ctDNA follow-up.

A pre-screening consent will be obtained for NGS analysis on tumor tissue. Only patients with at least 1 mutation at NGS on the tumor tissue will ultimately be enrolled in the study, to have the possibility to follow the mutation using ctDNA. Main consent will be obtained after results of the NGS and before initiation of pembrolizumab. Computed Tomography (CT)-scan imaging will be done every 9 weeks as part of routine care practice. 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. 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.

- Optional blood samples will be realized to analyse the degree of activity of the plasmatic lymphocytes.

Inclusion Criteria:

1. Histologically-proven NSCLC.
2. Age ≥ 18 years.
3. Advanced or metastatic stage IV.
4. Treatment-naïve patient.
5. Eligibility to first-line treatment with immune checkpoint inhibitor.
6. Measurable disease according to RECIST 1.1 criteria on CT-Scan.
7. Availability of expression of PD-L1 at immunohistochemistry analysis of the tumor biopsy.
8. No ALK or EGFR gene alteration.
9. Availability of tumor tissue for NGS analysis (7 slides).
10. PS 0 or 1.
11. Signed informed consent of the patient.

Exclusion Criteria:

1. No social security affiliation.
2. Person under legal protection.
3. Pregnant and breastfeeding women.

Patients can participate to another clinical trial that is not modifying immunotherapy or immunotherapy/chemotherapy treatment nor study follow-up ; after investigator's information

Sponsor will share de-identified data sets. Documents generated under the project will be disseminated in accordance with Institut Curie policies.

Data requests can be submitted starting 9 months after last article publication and will be made accessible for up to 12 months.

Access to trial individual participant data can be requested by qualified researchers engaging in independent scientific research, and will be provided following review and approval of a research proposal and Statistical Analysis Plan (SAP) and execution of a data sharing agreement (DSA).