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

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:

• Age ≥ 20 years at the time of consent.
• Histologically or cytologically confirmed diagnosis of non-small cell lung cancer (NSCLC).
• Presence of activating EGFR mutation (exon 19 deletion or L858R).
• Stage IV (metastatic) NSCLC at initial diagnosis.
• Completion of four cycles of first-line osimertinib plus platinum-based chemotherapy (FLAURA2 regimen).
• Radiologic evidence of disease control (complete response, partial response, or stable disease) after systemic therapy.
• Residual primary lung tumor suitable for local therapy (surgery or radiotherapy), as determined by multidisciplinary evaluation.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
• Adequate organ function based on institutional laboratory criteria.
• Ability to understand and willingness to provide written informed consent.

<Exclusion Criteria>

Participants will be excluded if they meet any of the following criteria:

• Radiologic or clinical evidence of progressive disease during first-line osimertinib-chemotherapy.
• Extensive, unresectable metastatic disease not amenable to local therapy.
• Untreated or clinically unstable brain metastases.
• Known contraindications to surgery or radiotherapy.
• Active second malignancy requiring concurrent treatment.
• Any condition that, in the opinion of the investigator, would interfere with study participation or interpretation of results.
• Pregnancy or breastfeeding at the time of enrollment.