Brief Summary The goal of this clinical trial is to evaluate the effect of postoperative adjuvant chemotherapy (ACT) in patients with stage I non-squamous non-small cell lung cancer (NSCLC) after curative resection.

The main questions it aims to answer are:

Does ACT improve recurrence-free survival (RFS) compared with observation alone?

Does ACT provide disease-free survival (DFS) benefit in this patient population?

Researchers will compare the adjuvant chemotherapy group with the observation group to see if chemotherapy reduces the risk of recurrence and improves survival outcomes.

Participants will:

Receive standard platinum-based adjuvant chemotherapy after surgery or undergo regular postoperative surveillance according to institutional guidelines.

Be followed at scheduled intervals with clinical assessments and imaging to monitor for recurrence and survival outcomes.

Inclusion Criteria:

1. Patients must have histologically confirmed non-squamous NSCLC
2. Patients must be ≥18 years of age at the time of diagnosis
3. Pathological stage I disease (T1-2N0M0) according to the AJCC 8th edition (specify if applicable)
4. Patients must have undergone complete surgical resection (R0) with systematic lymph node dissection
5. Surgery performed between January 1, 2015 and December 31, 2019

Exclusion Criteria:

1. Prior history of malignant tumors or presence of synchronous other primary malignancy
2. Multiple primary lung cancers diagnosed at baseline
3. Receipt of any neoadjuvant chemotherapy, radiotherapy, or targeted therapy
4. Perioperative death occurring within 30 days after surgery
5. Incomplete or missing clinical or pathological information
6. Loss to follow-up before the first scheduled surveillance assessment

patients with non-squamous NSCLC from four participating hospitals