This is a single-arm, open-label, phase II study evaluating the clinical outcomes of local therapy (surgery or radiotherapy) to the primary tumor in patients with EGFR-mutant advanced non-small cell lung cancer (NSCLC) who have achieved disease control following first-line treatment with the FLAURA2 regimen (osimertinib plus platinum-based chemotherapy). The primary objective is to assess the median progression-free survival (PFS) after local therapy.

This prospective, single-arm, multicenter observational study is designed to estimate the median progression-free survival (PFS) in patients with EGFR-mutant advanced non-small cell lung cancer (NSCLC) who receive salvage local treatment after achieving disease control with first-line osimertinib plus chemotherapy. A total of 70 patients will be enrolled. The primary endpoint is median PFS, and the sample size was calculated to ensure that the 95% confidence interval around the estimated median has a width of no more than ±3 months, using Greenwood's approximation. Patients will be followed for a minimum of 24 months after the last enrollment, with an overall study duration of up to 72 months.

<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.