Inclusion Criteria:

          -  Histologically confirmed non-squamous NSCLC harboring EGFR mutation positive but T790M
             mutation negative by local testing

          -  Unresectable stage UICC ≥ IIIb or metastatic stage UICC IV disease

          -  TKI naïve for metastatic NSCLC, neoadjuvant or adjuvant chemotherapy allowed

          -  At least one evaluable lesion according to RECIST v1.1

          -  Age ≥ 18 years

          -  ECOG performance status 0 - 2

          -  Adequate organ function, defined as all of the following:

               1. Absolute neutrophil count (ANC) ≥ 1500/mm3. (ANC > 1000/mm3 may be considered in
                  special circumstances such as benign cyclical neutropenia as judged by the
                  investigator and in discussion with the coordinating investigator)

               2. Platelet count ≥ 75,000/mm3

               3. Estimated glomerular filtration rate (eGFR) > 45 ml/min/1.73 m2 according to the
                  Cockcroft-Gault formula d. If history of cardiac comorbidity: Left ventricular
                  function with resting ejection fraction ≥ 50% or above the institutional lower
                  limit of normal (LLN)

             e. Total Bilirubin ≤ 1.5 times upper limit of normal (ULN), (if related to liver
             metastases ≤ 3 times ULN). (Patients with Gilbert's syndrome total Bilirubin must be ≤
             4 times institutional upper limit of normal) f. Aspartate amino transferase (AST) or
             alanine amino transferase (ALT) ≤ 3 times the upper limit of normal (ULN) (if related
             to liver metastases ≤ 5 times ULN)

          -  Recovered from any previous therapy related toxicity to ≤ Grade 1 at before
             randomization (except for stable sensory neuropathy ≤ Grade 2 and alopecia)

          -  Written informed consen

        Exclusion Criteria:

          -  Any investigational drug within 30 days or hormonal anticancer treatment within 2
             weeks prior to randomization (continued use of anti-androgens and/or gonadorelin
             analogues for treatment of prostate cancer permitted)

          -  T790M mutation positive tumors (by local testing)

          -  Radiotherapy within 2 weeks prior to randomization, except as follows:

               1. Palliative radiation to target organs other than chest may be allowed up to 1
                  week prior to randomization

               2. Single dose palliative treatment for symptomatic metastasis outside above
                  allowance to be discussed with coordinating investigator prior to enrolling

          -  Major surgery within 2 weeks before starting study treatment or scheduled for surgery
             during the projected course of the study

          -  Known hypersensitivity to afatinib or osimertinib or the excipients of any of the
             trial drugs

          -  History or presence of clinically relevant cardiovascular abnormalities such as

               1. uncontrolled hypertension

               2. congestive heart failure NYHA classification of ≥ 3

               3. unstable angina or poorly controlled arrhythmia as determined by the investigator

               4. Myocardial infarction within 6 months prior to randomization

               5. Clinically important abnormalities in rhythm and conduction as measured by
                  resting electrocardiogram (ECG) (e.g. QTc interval greater than 470 ms) or QTc
                  interval prolongation with signs/symptoms of serious arrhythmia

               6. Congenital long QT syndrome, congestive heart failure, electrolyte abnormalities,
                  or intake of medicinal products that are known to prolong the QTc interval

          -  Patients with a past or present medical history of

               1. Interstitial lung disease (ILD), drug-induced ILD, radiation pneumonitis that
                  required steroid treatment, or any evidence of clinically active ILD

               2. Any history of or concomitant condition that, in the opinion of the Investigator,
                  would compromise the patient's ability to comply with the study or interfere with
                  the evaluation of the efficacy and safety of the test drug

               3. Any history or presence of poorly controlled gastrointestinal disorders that
                  could affect the absorption of the study drug (e.g. Crohn's disease, ulcerative
                  colitis, chronic diarrhoea, malabsorption)

               4. Known active hepatitis B infection (defined as presence of HepB sAg and/ or Hep B
                  DNA), active hepatitis C infection (defined as presence of Hep C RNA) and/or
                  known HIV carrier

               5. Previous or concomitant malignancies at other sites, except effectively treated
                  non-melanoma skin cancers, carcinoma in situ of the cervix, ductal carcinoma in
                  situ or effectively treated malignancy that has been in remission for more than 5
                  years and is considered to be cured

          -  Pregnancy and contraception:

               1. Women who are pregnant, nursing, or who plan to become pregnant while in the
                  trial

               2. Women of child-bearing potential (WOCBP) and men who are able to father a child,
                  unwilling to be abstinent or use highly effective methods of birth control that
                  result in a low failure rate of less than 1% per year when used consistently and
                  correctly beginning at informed consent, for the duration of study participation
                  and for at least 2 months for females and 4 months for males after last dose

          -  Requiring treatment with any of the prohibited concomitant medications protein
             Inhibitors/Inductors CYP3A4/5 Inhibitors/Inductors that cannot be stopped for the
             duration of trial participation or concomitant St. John's Wort

          -  Uncontrolled brain metastases (Patients with brain or subdural metastases are not
             eligible, unless they have completed local therapy (≤ 2 weeks apart from last
             radiotherapy or radiosurgery) and have discontinued the use of corticosteroids,
             anticonvulsants or have been on stable dose of corticosteroids (i.e. Dexamethasone ≤ 8
             mg) for at least 4 weeks before starting study treatment. Any symptoms attributed to
             brain metastases must be stable for at least 4 weeks before starting study treatment)
             or Leptomeningeal carcinomatosis 11. Other contraindications to study treatment
             (Investigators opinion) or legal incapacity or limited legal capacity