Segmentectomy vs Lobectomy for 2 - 3cm IASLC Grade 1-2 Lung Adenocarcinoma: A Multi-center RCT

1. Initial Registration (1.1) Inclusion Criteria: 1. Aged 20 to 79 years, regardless of gender. 2. Preoperative CT or PET-CT suggests: ① Imaging diameter of 2-3 cm. * Suspicion of non-small cell lung cancer (NSCLC). * Solitary nodule or concomitant lesions with microinvasion or below. * Primary tumor not located in the middle lobe. * No suspected lymph node involvement. 3. Preoperative CT lung window (window level -700HU, window width 1500HU) indicates the nodule is predominantly solid, i.e., the consolidation-to-tumor ratio (CTR) is greater than 0.5 (CTR \> 0.5). 4\. Good lung function (FEV1 \> 1.5 L or FEV1% ≥ 60%), tolerable for both segmentectomy and lobectomy. 5\. Eastern Cooperative Oncology Group (ECOG) performance status 0 to 2. 6. Voluntary participation with signed informed consent, able to comply with study visit plans and other protocol requirements. 7\. No history of ipsilateral thoracotomy; video-thoracoscopic examination meets the criteria. 8\. No history of chemotherapy or radiotherapy, including treatment for other cancers. Eligible if more than 5 years have passed since completion of perioperative adjuvant chemotherapy. Eligible if there is a history of or ongoing hormone therapy. 9\. All the following laboratory test results are eligible (all laboratory tests use the latest results within 28 days before initial registration; laboratory tests on the same day within 4 weeks before initial registration are allowed): * White blood cell count ≥ 3000/mm³. * Hemoglobin ≥ 8.0 g/dL (without blood transfusion within 28 days before initial registration). * Platelet count ≥ 10×10⁴/mm³. * AST ≤ 100 IU/L. ⑤ ALT ≤ 100 IU/L. ⑥ Total bilirubin ≤ 2.0 mg/dL. ⑦ Serum creatinine ≤ 1.5 mg/dL. 10. The patient has signed a written informed consent. (1.2) Exclusion Criteria: 1. Active bacterial or fungal infection (confirmed by imaging diagnosis or bacteriological examination with fever \>38°C). 2. Multiple active cancers (synchronous or metachronous multiple primary cancers, excluding in situ carcinoma or intramucosal cancer lesions considered cured by local treatment; such lesions are not included in active multiple cancers). 3. Patients with severe impairment of cardiac, hepatic, or renal function (cardiac function grade 3-4; ALT and/or AST more than 3 times the upper limit of normal; Cr exceeding the upper limit of normal). 4. Patients with concomitant other malignant tumors or hematological diseases. 5. Pregnant, planning to become pregnant, or lactating female patients (diagnosed with early pregnancy when urine HCG \>2500 IU/L). 6. Any form of antitumor therapy before tumor resection, including interventional chemotherapy embolization, ablation, radiotherapy, chemotherapy, and molecular targeted therapy. 7. Patients who participated in other tumor-related clinical trials within the past three months. 8. Preoperative CT suggests ground-glass predominant nodules (CTR \< 0.5). 9. Patients with positive lymph nodes indicated by preoperative imaging or lymph node puncture (clinical N stage = 1 or 2). 10. Patients with tumors near the hilum who cannot undergo segmentectomy. 11. Patients deemed unsuitable for enrollment by the investigator. 2. Intraoperative Secondary Registration (2.1) Inclusion Criteria: 1. Intraoperative frozen section indicates invasive lung adenocarcinoma with International Association for the Study of Lung Cancer (IASLC) grade 1-2 (\<20% pathological high-grade subtypes). 2\. Intraoperative frozen section shows negative surgical margins. 3. Intraoperative exploration reveals no severe adhesions or lymph node inflammatory changes (adhesions of pulmonary vessels or bronchi), confirming feasibility for both lobectomy and segmentectomy. (2.2) Exclusion Criteria: 1. Patients with IASLC grade 3 (≥20% pathological high-grade subtypes) indicated by intraoperative frozen section. 2. Patients confirmed with in situ carcinoma or microinvasive adenocarcinoma by intraoperative frozen section. 3. Patients with preoperative findings of distant metastasis or pleural/ascitic effusion.