Inclusion Criteria:

          -  Males and females >=18 years of age

          -  Histologically or cytologically confirmed non-small cell lung cancer (NSCLC),
             performed on a biopsy that occurred within the last 90 days

          -  Documented activating EGFR mutation (Exon 19 deletion, T790M, or L858R) on tumor
             samples by Clinical Laboratory Clinical Laboratory Improvement Amendments
             (CLIA)-approved test

          -  Positron emission tomography (PET)-computed tomography (CT) within the last 60 days
             showing radiographic stage I to IIIa lung cancer (mediastinal staging biopsy is
             allowed but not required)

          -  Brain magnetic resonance imaging (MRI) (or CT if contraindication to MRI) within the
             last 60 days showing no evidence of metastatic disease

          -  Documentation that the patient is a candidate for surgical resection of their lung
             cancer by an American Board of Thoracic Surgery certified surgeon

          -  The patient must have a tumor size >=1 centimeter (cm) in its longest diameter.

          -  Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) of 0-1

          -  Any unresolved toxicities from prior therapy greater than Common Terminology Criteria
             for Adverse Events (CTCAE) grade 1 at the time of starting study treatment, with the
             exception of alopecia and grade 2 prior platinumtherapy-related neuropathy is allowed

          -  Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) =< 2.5 x upper
             limit of normal (ULN)

          -  Bilirubin =< 1.5 x ULN, (Patients with documented Gilbert's syndrome and conjugated
             bilirubin within the normal range may be allowed into the study; in this event, it
             will be documented that the patient was eligible based on conjugated bilirubin levels)

          -  Potassium and magnesium within normal range, patients may receive supplements to meet
             this requirement

          -  Leukocytes > 3,000/microliter (mcL)

          -  Hemoglobin >= 9 g/dL, with no blood transfusions in the 28 days prior to study entry

          -  Absolute neutrophil count > 1,500/mcL

          -  Platelets > 100,000/mcL

          -  Creatinine =< 1.5 x upper limit of normal (ULN) OR creatinine clearance > 50
             mL/min/1.73 m2 for patients with creatinine levels =< 1.5 x upper limit above
             institutional normal

          -  Ability to swallow oral medications

          -  Women of childbearing potential (WoCBP) must have a negative serum pregnancy test
             within 3 days prior to the first dose of study treatment and agree to use highly
             effective contraception, during the study and for 90 days following the last dose of
             osimertinib

               -  Women of childbearing potential (WoCBP): women between menarche and menopause who
                  have not been permanently or surgically sterilized and are capable of procreation

               -  Women NOT of childbearing potential: women who are permanently or surgically
                  sterilized or postmenopausal

                    -  Permanent sterilization includes hysterectomy and/or bilateral oophorectomy
                       and/or bilateral salpingectomy but excludes bilateral tubal occlusion; tubal
                       occlusion is considered a highly effective method of birth control but does
                       not absolutely exclude possibility of pregnancy; (the term occlusion refers
                       to both occluding and ligating techniques that do not physically remove the
                       oviducts)

               -  Women who have undergone tubal occlusion should be managed on trials as if they
                  are of WoCBP (e.g. undergo pregnancy testing etc., as required by the study
                  protocol)

               -  Women will be considered postmenopausal if they are amenorrhoeic for 12 months
                  without an alternative medical cause; the following age-specific requirements
                  apply:

                    -  Women under 50 years old will be considered postmenopausal if they have been
                       amenorrhoeic for 12 months or more following cessation of exogenous hormonal
                       treatments and with luteinizing hormone and follicle-stimulating hormone
                       levels in the postmenopausal range

                    -  Women over 50 years of age will be considered postmenopausal if they have
                       been amenorrhoeic for 12 months or more following cessation of all exogenous
                       hormonal treatments

               -  Acceptable contraception methods are:

                    -  Total sexual abstinence (abstinence must be for the total duration of the
                       trial and the follow-up period)

                    -  Vasectomized sexual partner plus male condom (with participant assurance
                       that partner received post-vasectomy confirmation of azoospermia)

                    -  Tubal occlusion plus male condom

                    -  Intra-uterine device - provided coils are copper-banded, plus male condom

                    -  Intra-uterine system (IUS) levonorgestrel IUS (e.g., Mirena), plus male
                       condom

                    -  Medroxyprogesterone injections (Depo-Provera) plus male condom

                    -  Etonogestrel implants (e.g., Implanon, Norplan) plus male condom

                    -  Normal and low dose combined oral contraceptive pills, plus male condom

                    -  Norelgestromin / ethinylestradiol transdermal system plus male condom

                    -  Intravaginal device (e.g., ethinylestradiol and etonogestrel) plus male
                       condom

                    -  Cerazette (desogestrel) plus male condom (Cerazette is currently the only
                       highly efficacious progesterone based pill)

               -  Unacceptable Contraception Methods The following methods are considered not to be
                  highly effective and are therefore not acceptable contraceptive methods:

                    -  Triphasic combined oral contraceptives

                    -  All progesterone only pills except, Cerazette

                    -  All barrier methods, if intended to be used alone

                    -  Non-copper containing intra-uterine devices

                    -  Fertility awareness methods

                    -  Coitus interruptus

          -  Men with a female partner of childbearing potential must have either had a prior
             vasectomy agree to use effective contraception as described in the full protocol for
             at least 14 days prior to administration of the first dose of study treatment, during
             the study, and for 90 days following the last dose of osimertinib

        Exclusion Criteria:

          -  Leptomeningeal carcinomatosis or other central nervous system (CNS) metastases

          -  Stage IIIB, or distant metastases (including malignant pleural effusion) identified on
             PET-CT scan or biopsy (PET abnormalities that are negative for malignancy on biopsy
             will be considered on a case by case basis

          -  Past medical history of interstitial lung disease, drug-induced interstitial lung
             disease, radiation pneumonitis which required steroid treatment, or any evidence of
             clinically active interstitial lung disease

          -  Patients who are known to be serologically positive for human immunodeficiency virus
             (HIV)

          -  Active second malignancy, i.e. patient known to have potentially fatal cancer present
             for which he/she may be (but not necessarily) currently receiving treatment; patients
             with a history of malignancy that has been completely treated, with no evidence of
             that cancer currently, are permitted to enroll in the trial provided all chemotherapy
             for prior malignancy was completed > 12 months prior and/or bone marrow transplant > 2
             years prior

          -  Patients who are currently receiving treatment with contraindicated corrected QT
             interval (QTc) prolonging medications or potent CYP3A4 inducers, if that treatment
             cannot be either discontinued or switched to a different medication prior to first day
             of study treatment. All patients must try to avoid concomitant use of any medications,
             herbal supplements and/or ingestion of foods with known inducer effects

          -  Any of the following cardiac abnormalities or history:

               -  Mean resting corrected QT interval (QTc) > 470 msec, obtained from 3
                  electrocardiograms (ECGs), using the screening clinic ECG machine derived QTc
                  value

               -  Any clinically important abnormalities in rhythm, conduction or morphology of
                  resting ECG e.g. complete left bundle branch block, third degree heart block and
                  second degree heart block

               -  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

          -  Prior treatment with osimertinib or other drugs that target EGFR mutant non-small cell
             lung cancer (including erlotinib, afatinib, gefitinib, rocelitinib)

          -  Treatment with prohibited medications (concurrent anticancer therapy including
             chemotherapy, radiation, hormonal treatment [except corticosteroids and
             megesterolacetate], or immunotherapy) =< 14 days prior to treatment with osimertinib

          -  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 jeopardize
             compliance with the protocol, or known active infection including chronic active
             hepatitis B, hepatitis C and human immunodeficiency virus (HIV); screening for chronic
             conditions is not required; patients with chronic hepatitis B virus (HBV) with
             negative HBV viral load on appropriate antiviral therapy will be permitted, if able to
             continue appropriate antiviral therapy throughout treatment period

          -  Active tuberculosis

          -  Signs or symptoms of infection within 2 weeks prior to first day of study

          -  Therapeutic oral or intravenous (IV) antibiotics within 2 weeks prior to first day of
             study treatment:

               -  Patients receiving prophylactic antibiotics (eg, to prevent a urinary tract
                  infection or chronic obstructive pulmonary disease exacerbation) are eligible

          -  Class II to IV heart failure as defined by the New York Heart Association functional
             classification system

          -  Patients with known coronary artery disease, congestive heart failure not meeting the
             above criteria, or left ventricular ejection fraction (LVEF) < 50% must be on a stable
             medical regimen that is optimized in the opinion of the treating physician, in
             consultation with a cardiologist if appropriate, to be eligible

          -  Patients who have experienced untreated and/or uncontrolled cardiovascular conditions
             and/or have symptomatic cardiac dysfunction (unstable angina, congestive heart
             failure, myocardial infarction within the previous 3 months; coronary angioplasty, or
             stenting or bypass grafting within the past 6 months; cardiac ventricular arrhythmias
             requiring medication; any history of second (2nd) or third (3rd) degree
             atrioventricular conduction defects)

          -  Females who are pregnant or breastfeeding

          -  Presence of active gastrointestinal (GI) disease (including GI bleeding or ulceration)
             or other condition that could affect GI absorption (e.g. malabsorption syndrome,
             history of biliary tract disease), including refractory nausea or vomiting, or chronic
             GI disease which may affect absorption or tolerance to oral medications

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

          -  Involvement in the planning and/or conduct of the study (applies to both investigator
             staff and/or staff at the study site)

          -  Participation in another clinical study with an investigational product during the
             last 2 months or within five half-lives of the compound, whichever is longer

          -  Uncontrolled medical, psychological, familial, sociological, or geographical
             conditions that interfere with the patient?s safety, ability to provide informed
             consent, or ability to comply with the protocol