Inclusion Criteria:

          1. Written informed consent;

          2. Male or female patient aged ≥18 years;

          3. Histologically/cytologically confirmed diagnosis of stage IIIB/IV NSCLC with evidence
             of activating EGFR mutations including exon 19 deletion, exon 21 L858R or other
             activating/sensitizing EGFR mutations such as exon 21 L861Q, exon 18 G719S, G719A,
             G719C, exon 20 S768I and V769L; co-occurrence of de novo T790M is not an exclusion
             criterion; EGFR status assessed in circulating DNA is allowed;

          4. Patients eligible and candidate to receive osimertinib as first- or second-line
             treatment according to clinical practice and study design, as decided by Investigator
             regardless study participation;

          5. Patients with brain metastases are allowed provided they are asymptomatic and stable
             (i.e. without evidence of progression by imaging for at least two weeks prior to the
             first dose of trial treatment and without deterioration of any neurologic symptoms);

          6. No evidence of concomitant drivers including KRAS mutations, HER2 mutations, ALK or
             ROS1 rearrangements, MET mutations, BRAF mutations;

          7. No previous EGFR-TKI therapy; Previous palliative radiotherapy or surgery allowed.
             Prior brain radiotherapy and Stereotactic Radiosurgery (SRS) are allowed. Previous
             neo/adjuvant chemotherapy is allowed as long as therapy was completed at least 6
             months before diagnosis of advanced or metastatic NSCLC;

          8. At least one radiological measurable disease according to RECIST criteria version 1.1;

          9. Performance status 0-1 (ECOG PS);

         10. Patient compliance to trial procedures;

         11. Adequate bone marrow function (ANC ≥ 1.5x109/L, platelets ≥100x109/L, haemoglobin >9
             g/dl);

         12. Adequate liver function (AST (SGOT)/ALT (SGPT) ≤2.5 x institutional upper limit of
             normal unless liver metastases are present, in which case it must be ≤5x ULN,
             bilirubin < grade 2, transaminases no more than 3xULN/<5xULN in presence of liver
             metastases);

         13. Normal level of alkaline phosphatase, and creatinine;

         14. Female patients should be using adequate contraceptive measures, should not be
             breastfeeding, until 12 months after the last dose, and must have a negative pregnancy
             test (serum or urine) prior to first dose of study drug (within 72 hours); or female
             patients must have an evidence of non-childbearing potential by fulfilling one of the
             following criteria at screening:

               -  Post-menopausal defined as aged more than 50 years and amenorrheic for at least
                  12 months following cessation of all exogenous hormonal treatments.

               -  Women under 50 years old would be consider postmenopausal if they have been
                  amenorrheic for 12 months or more following cessation of exogenous hormonal
                  treatments and with luteinizing hormone (LH) and follicle-stimulating hormone
                  (FSH) levels in the post-menopausal range for the institution. Documentation of
                  irreversible surgical by hysterectomy, bilateraloophorectomy, or bilateral
                  salpingectomy but not tubal ligation.

         15. Male patients should be willing to use barrier contraception, i.e. condoms;

         16. No significant comorbidity that according to the investigator would hamper the
             participation on the trial;

        Exclusion Criteria:

          1. Previous therapy with any EGFR-TKI;

          2. Previous systemic anti-cancer therapy for advanced/metastatic NSCLC including
             chemotherapy, biologic therapy, immunotherapy, or any investigational drug;

          3. Absence of measurable lesions;

          4. Concomitant radiotherapy or chemotherapy;

          5. Symptomatic or immediately requiring therapy brain metastases or carcinomatous
             meningitis. Subjects with asymptomatic and stable or treated brain metastases may
             participate;

          6. Diagnosis of any other malignancy during the last 3 years, except for in situ
             carcinoma of cervix uteri and squamous cell carcinoma of the skin;

          7. History of extensive disseminated/bilateral or known presence of Grade 3 or 4
             interstitial fibrosis or interstitial lung disease including a history of pneumonitis,
             hypersensitivity pneumonitis, interstitial pneumonia, interstitial lung disease,
             obliterative bronchiolitis and pulmonary fibrosis (but not history of prior radiation
             pneumonitis);

          8. Any evidence of severe or uncontrolled systemic diseases, including uncontrolled
             hypertension and active bleeding diatheses; or active infection including hepatitis B,
             hepatitis C and human immunodeficiency virus (HIV);

          9. Refractory nausea and vomiting, chronic gastrointestinal diseases, inability to
             swallow the formulated product, or previous significant bowel resection that would
             preclude adequate absorption of the study drugs;

         10. Any of the following cardiac criteria:

               -  Mean resting corrected QT interval (QTc) >470 msec, obtained from 3 ECGs using
                  local clinic ECG machine-derived QTcF value;

               -  Any clinically important abnormalities in rhythm, conduction, or morphology of
                  resting ECG, e.g., complete left bundle branch block, third-degree heart block,
                  second-degree heart block, PR interval >250 msec or history of episodes of
                  bradycardia (<50 BPM);

               -  Any factors that increase the risk of QTc prolongation or risk of arrhythmic
                  events such as heart failure, hypokalaemia, congenital long QT syndrome family
                  history of long QT syndrome, or unexplained sudden death under 40 years of age in
                  first-degree relatives or any concomitant medication known to prolong the QT
                  interval;

               -  Abnormal cardiac function: LVEF < 50% (assessed by MUGA or ECHO)

         11. Pregnancy or lactating female;

         12. Other serious illness or medical condition potentially interfering with the study.