Inclusion Criteria:

   1. Patients must be 18 or the legal age of consent in the jurisdiction in which the study
   is taking place, at the time of signing the informed consent form.

   2. Patients with histologically documented NSCLC of predominantly non-squamous, squamous,
   and adenosquamous pathology who present with locally advanced, unresectable (Stage
   III) disease (according to Version 8 of the IASLC Staging Manual in Thoracic
   Oncology). It is recommended but not required that except for overt cT4 disease, nodal
   status N2, or N3 should have been proven by biopsy, via endobronchial ultrasound,
   mediastinoscopy, thoracoscopy, or in absence of biopsy, should have been confirmed
   with whole body 18FDG PET plus contrast-enhanced CT in addition to or in combination
   with PET.

   3. Patient who are eligible for and - planning to undergo CCRT or SCRT treatment.

   4. Patients who had recurred from Stage I/II/III after complete surgery or had gross
   incomplete resections can be included if they didn't receive treatment with any
   chemotherapy, radiation therapy, immunotherapy, targeted therapy, or investigational
   agents.

   5. Availability of the EGFRm test results confirming that the tumour harbours one of the
   two common EGFR mutations known to be associated with EGFR-TKI sensitivity (Ex19del,
   L858R), either alone or in combination with other EGFR mutations including de novo
   T790M

   6. WHO performance status of 0 or 1 with no deterioration over the previous 2 weeks prior
   to baseline at screening and prior to first dose.

   7. Minimum life expectancy of > 12 weeks at Day 1.

   8. At least one lesion that can be accurately measured at baseline as ≥ 10 mm in the
   longest diameter (except lymph nodes, which must have short axis ≥ 15 mm) with CT or
   MRI and is suitable for accurate repeated measurements.

   9. Adequate organ and bone marrow function

10. Male and/or female. Contraceptive use by males or females should be consistent with
   local regulations regarding the methods of contraception for those participating in
   clinical studies

11. Capable of giving signed informed consent, which includes compliance with the
   requirements and restrictions listed in the ICF and in this CSP.

12. Provision of signed and dated written Optional Genomics Initiative Research
   Information and Consent Form prior to collection of samples for optional genomics
   initiative research that supports the Genomic Initiative

Exclusion Criteria:

   1. Any presence of small cell and mixed small-cell and non-small cell histology.

   2. Past medical history of ILD/pneumonitis, drug-induced ILD, radiation pneumonitis that
   required steroid treatment, or any evidence of clinically active ILD/pneumonitis.

   3. Any unresolved toxicities from prior therapy greater than CTCAE Grade 1 at the time of
   starting study treatment with the exception of alopecia. Patients with irreversible
   toxicity that is not reasonably expected to be exacerbated by study intervention in
   the opinion of the investigator may be included after consultation with the
   AstraZeneca medical monitor (eg, hearing loss).

   4. Any evidence of severe or uncontrolled systemic diseases, including uncontrolled
   hypertension and active bleeding diatheses, which in the investigator's opinion makes
   it undesirable for the patient to participate in the trial or which would jeopardise
   compliance with the protocol, or active infection (eg, patients receiving treatment
   for infection, including HCV, HIV, and tuberculosis) or active uncontrolled HBV
   infection.

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

   6. History of another primary malignancy except for malignancy treated with curative
   intent with no known active disease ≥ 2 years before the first dose of study
   intervention and of low potential risk for recurrence. Exceptions include adequately
   resected non-melanoma skin cancer and curatively treated in situ disease. Patients who
   have received RT with overlapping fields (eg, cured breast cancer) should be excluded.

   7. Patient meets any of the following cardiac criteria:

      1. Mean resting QTc > 470 msec, obtained from 3 ECGs, using the screening clinic ECG
      machine-derived QTc value.

      2. Any clinically important abnormalities in rhythm, conduction or morphology of
      resting ECG eg, complete left bundle branch block, third degree heart block and
      second-degree heart block. Patients with atrial fibrillation controlled by
      medication or arrhythmias controlled by pacemakers may be permitted based on the
      investigator judgement with cardiologist consultation recommended.

      3. History of QT prolongation associated with other medications that required
      discontinuation of that medication.

   8. Congenital long QT syndrome, family history of long QT syndrome, unexplained sudden
   death under 40 years of age in first-degree relatives or patients with any factors
   that increase the risk of QTc prolongation/arrhythmic events such as electrolyte
   abnormalities, heart failure or any concomitant medication known to prolong the QT
   interval and cause TdP.

   9. Patients currently receiving (or unable to stop use prior to receiving the first dose
   of study treatment) medications or herbal supplements known to be strong inducers of
   CYP3A4 (at least 3-week prior to dosing). All patients must try to avoid concomitant
   use of any medications, herbal supplements and/or ingestion of foods with known
   inducer effects on CYP3A4.

10. Prior treatment with any chemotherapy, radiation therapy, immunotherapy or
   investigational agents for locally advanced, unresectable Stage III NSCLC. Prior
   surgical resection (ie, Stage I, II, or III) with no systemic treatment with residual
   disease or a recurrence is permitted.

11. Prior exposure to EGFR-TKI therapy

12. Major surgical procedure (excluding placement of vascular access) or significant
   traumatic injury within 4 weeks of the first dose of study intervention or an
   anticipated need for major surgery during the study.

13. Participation in another clinical study with a study intervention or investigational
   medicinal device administered in the last 4 weeks (unless the safety profile is known
   prior to first dose of study intervention), or concurrent enrolment in another
   clinical study (unless the study is observational [noninterventional], or the patient
   is in the followup period of an interventional study).

14. History of hypersensitivity to active or inactive excipients of osimertinib or drugs
   with a similar chemical structure or class to osimertinib.

15. History of hypersensitivity to active or inactive excipients of the chemotherapy
   regimen of choice (pemetrexed or paclitaxel; cisplatin or carboplatin) or RT or drugs
   with a similar chemical structure or class to the chemotherapy.

16. Involvement in the planning and/or conduct of the study (applies to both AstraZeneca
   staff and/or staff at the study site).

17. Judgment by the investigator that the patient should not participate in the study if
   the patient is unlikely to comply with study procedures, restrictions, and
   requirements.

18. Previous enrolment in the present study. Rescreening of individuals who were screen
   failures is allowed.

19. For females only: Currently pregnant (confirmed with positive pregnancy test) or
   breastfeeding.

20. Patients should refrain from breastfeeding from enrolment throughout the study and
   until 6 weeks after last dose of study intervention.

21. In addition, the following are considered criteria for exclusion from the exploratory
   genetic research:

      - Prior allogeneic bone marrow transplant.

      - Non-leukocyte depleted whole blood transfusion within 120 days of genetic sample
      collection.