A Prospective Cohort Study to Evaluate Molecular pRognostic Factors and Resistance Mechanisms to Osimertinib in Adjuvant Treatment of Completely Resected pIB-IIIA Non-small Cell Lung Carcinoma With Common EGFR Mutations (L858R and Del19)

Inclusion Criteria: 1. Signed Informed consent. 2. Age ≥ 18 years. 3. Pre-surgical disease evaluation including brain MRI/CT-scan and total body PET-FDG CT-scan prior to surgery. 4. Histologically complete anatomical resection (R0) of stage pIB-IIIA (pTNM 8th edition) NSCLC. 5. Presence of a common EGFR mutation (Del19 or L858R). 6. Archival tumour tissue FFPE blocks from surgery available for centrally molecular analyses. 7. Patient eligible to receive osimertinib adjuvant therapy in a 3-year intent to treat decision; patients could receive if necessary adjuvant chemotherapy before starting osimertinib treatment. 8. Patient who is capable, according to the investigator, of complying with the study's requirements and restrictions. 9. Patient followed in the institution on a regular basis (every 3 to 6 months) according to standard recommendations. 10. Estimated life expectancy \> 3 years. 11. Woman patients who are of childbearing potential are eligible: * They must have a negative pregnancy test before the first dose of osimertinib. * They must agree to use effective methods of contraception throughout the course of treatment and should be maintained for 2 months after the end of treatment. 12. Male subjects who are sexually active with a woman of childbearing potential are eligible if an efficacious contraception method should be used during the treatment and during the 4 months following the last dose. Exclusion Criteria: 1. History of cancer, except for the following situations: Patients with history of cancer for more than 3 years are eligible if they have been treated and considered cured. Patients with history of in situ carcinoma of the cervix or non-melanoma skin carcinoma are eligible. 2. Neoadjuvant anti-cancer treatment (osimertinib and/or chemotherapy or other anti-cancer treatment). 3. Incompletely resected NSCLC (R1 or R2). 4. Any medical condition that would, according to the investigator's judgment, prevent the patient's participation in the clinical study. 5. Active infection (e.g. patients receiving treatment for infection) including hepatitis C virus (HCV) and human immunodeficiency virus (HIV), or active uncontrolled hepatitis B infection except for the situations described in APPENDIX I. Screening for chronic conditions is not required.