During the surgery for non-small cell lung cancer (NSCLC), lymphadenectomy or lobectomy are performed first, different surgeons have different choices. Oncology textbooks require dissecting distant lymph nodes (LNs) first and then dissecting nearby LNs. According to this requirement, thoracic surgeons should first perform lymphadenectomy and then lobectomy. Unfortunately, there is no high-level evidence to prove which surgical sequence is more beneficial to the long-term survival of NSCLC patients. In this multi-center randomized controlled trial (RCT), patients with stage I-II NSCLC were enrolled as the research object to determine which surgical sequence (lymphadenectomy-first vs. lobectomy-first) is better for the short-term and long-term outcomes in NSCLC patients.

Inclusion Criteria:

1. Age from 18 to 80 years old;
2. The first clinical diagnosis before surgery was non-small cell lung cancer, including adenocarcinoma, squamous cell carcinoma, large cell carcinoma, and other unknown types;
3. Clinical stage T1-2N0-1 (cI-II): Maximum diameter of tumor <= 5 cm and short diameter of mediastinal lymph node <= 1cm in thin layer computed tomography (CT);
4. The patient's physical condition is able to tolerate lobectomy: (1) Goldman index 0-1; (2) Predicted forced expiratory volume in 1s (FEV1) >= 40% and diffusing capacity of the lung for carbon monoxide (DLCO) >= 40%; (3) Total bilirubin <= 1.5 upper limit of normal; (4) Alanine aminotransferase (ALT)/Aspartate aminotransferase (AST) <= 2.5 upper limit of normal; (5) Creatinine <= 1.25 upper limit of normal and creatinine clearance rate (CCr) >= 60 ml/min;
5. Performance status of Eastern Cooperative Oncology Group (ECOG) = 0-1;
6. All relevant examinations were completed within 28 days before the operation;
7. Patients who understand this study and have signed an approved Informed Consent.

Exclusion Criteria:

1. Patients who have undergone anti-tumor therapy (radiotherapy, chemotherapy, targeted therapy, immunotherapy) before surgery;
2. Patients with previous medical history of other malignant tumors or combined with second primary cancer at the time of enrollment;
3. Patients who meet all of the following criteria are eligible for sublobar resection (segment/wedge resection): (1) Ground glass opacity (GGO) with a solid component <= 50%; (2) The largest diameter of nodule is <= 2 cm; (3) The nodule is located in the outer third of the lung field;
4. Patients with preoperative diagnosis of pure GGO;
5. Patients with previous medical history of unilateral thoracotomy;
6. Women who are pregnant or breastfeeding;
7. Patients with active bacterial or fungal infection that is difficult to control;
8. Patients with serious psychosis;
9. Patients with a history of severe heart disease, heart failure, myocardial infarction or angina pectoris in the past 6 months.