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-FDGCT-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 molecularanalyses.
7. Patient eligible to receive osimertinib adjuvant therapy in a 3-year intent to treatdecision; patients could receive if necessary adjuvant chemotherapy before startingosimertinib treatment.
8. Patient who is capable, according to the investigator, of complying with the study'srequirements and restrictions.
9. Patient followed in the institution on a regular basis (every 3 to 6 months) accordingto 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 courseof 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 areeligible if an efficacious contraception method should be used during the treatmentand 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 beentreated and considered cured. Patients with history of in situ carcinoma of the cervixor non-melanoma skin carcinoma are eligible.
2. Neoadjuvant anti-cancer treatment (osimertinib and/or chemotherapy or otheranti-cancer treatment).
3. Incompletely resected NSCLC (R1 or R2).
4. Any medical condition that would, according to the investigator's judgment, preventthe patient's participation in the clinical study.
5. Active infection (e.g. patients receiving treatment for infection) including hepatitisC virus (HCV) and human immunodeficiency virus (HIV), or active uncontrolled hepatitisB infection except for the situations described in APPENDIX I. Screening for chronicconditions is not required.