Inclusion Criteria:  Participants are eligible to be included in the study only if all of the following criteria apply:  Capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol. Provision of signed and dated, written informed consent form prior to any mandatory study-specific procedures, sampling, and analyses. Male or female, age at least 18 years. Type of Participant and Disease Characteristics Pathologically confirmed non-small cell lung cancer (NSCLC) with documented EGFR sensitive mutation (EGFR 19del and L858R) positive before Osimertinib 1L. Locally advanced (clinical stage IIIB, IIIC) or metastatic NSCLC(clinical stage IVA or IVB) or recurrent NSCLC (per Version 8 of the International Association for the Study of Lung Cancer [IASLC] Staging Manual in Thoracic Oncology), not amenable to curative or radiotherapy (e.g., this may occur as systemic recurrence after prior surgery for early stage disease or patients may be newly diagnosed with stage IIIB/IV disease, which is at the start of Osimertinib therapy). Patients must have been treated with Osimertinib as first line therapy until disease progression. Evidence of disease progression following 1L Osimertinib can be confirmed by investigators with criteria in Response Evaluation Criteria in Solid Tumours (RECIST) Version 1.1.  Agree to provide adequate tissue and whole blood for testing after disease progression following 1L Osimertinib.  Reproduction  Female participants who are not abstinent (in line with the preferred and usual lifestyle choice of the participant) and intend to be sexually active with a male partner must be using highly effective contraceptive measures, must not be breast feeding, and must have a negative pregnancy test prior to first dose of study intervention or must have evidence of non-child-bearing potential by fulfilling 1 of the following criteria at screening:  Post-menopausal, defined as more than 50 years of age and amenorrhoeic for at least 12 months following cessation of all exogenous hormonal treatments Women under 50 years old would be considered as postmenopausal if they have been amenorrhoeic for 12 months or more following cessation of exogenous hormonal treatments and have luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels in the post-menopausal range for the institution Documentation of irreversible surgical sterilization by hysterectomy, bilateral oophorectomy or bilateral salpingectomy but not tubal ligation.  Further information is available in Appendix E (Definition of Women of Childbearing Potential and Acceptable Contraceptive Methods).  Male participants must be willing to use barrier contraception.  Exclusion Criteria:  Participants are excluded from the study if any of the following criteria apply:  Any concurrent and/or other active malignancy that may affect tissue or whole blood testing results.  As judged by the investigator, any evidence of severe or uncontrolled systemic diseases, including uncontrolled hypertension, active bleeding diseases, which in the investigator's opinion, makes it undesirable for the participant to participate in the study or that would jeopardise compliance with the protocol, or active infection including hepatitis B, hepatitis C and human immunodeficiency virus (HIV). Screening for chronic conditions is not required.  Prior/Concomitant Therapy  Any concurrent anticancer treatment. Concurrent use of hormonal therapy for non cancer related conditions (eg, hormone replacement therapy) is allowed.  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.  Other Exclusions  Involvement in the planning and/or conduct of the study (applies to both AstraZeneca staff and/or staff at the study site).  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.