Bolstering Outcomes After Induction With Osimertinib Plus Chemotherapy Through Optimized Site-Directed Primary Tumor Therapy (BOOST Trial)

\<Inclusion Criteria\> Participants must meet all of the following criteria to be eligible: 1. Age ≥ 20 years at the time of consent. 2. Histologically or cytologically confirmed diagnosis of non-small cell lung cancer (NSCLC). 3. Presence of activating EGFR mutation (exon 19 deletion or L858R). 4. Stage IV (metastatic) NSCLC at initial diagnosis. 5. Completion of four cycles of first-line osimertinib plus platinum-based chemotherapy (FLAURA2 regimen). 6. Radiologic evidence of disease control (complete response, partial response, or stable disease) after systemic therapy. 7. Residual primary lung tumor suitable for local therapy (surgery or radiotherapy), as determined by multidisciplinary evaluation. 8. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. 9. Adequate organ function based on institutional laboratory criteria. 10. Ability to understand and willingness to provide written informed consent. \<Exclusion Criteria\> Participants will be excluded if they meet any of the following criteria: 1. Radiologic or clinical evidence of progressive disease during first-line osimertinib-chemotherapy. 2. Extensive, unresectable metastatic disease not amenable to local therapy. 3. Untreated or clinically unstable brain metastases. 4. Known contraindications to surgery or radiotherapy. 5. Active second malignancy requiring concurrent treatment. 6. Any condition that, in the opinion of the investigator, would interfere with study participation or interpretation of results. 7. Pregnancy or breastfeeding at the time of enrollment.