Septum-guided Segmentectomy for 2-3 cm Clinical Stage IA3 Peripheral Non-Small Cell Lung Cancer

Inclusion Criteria:

* Age 18 to 80 years, male or female.
* Clinical stage IA3 non-small cell lung cancer according to the International Association for the Study of Lung Cancer 9th edition tumor, node, metastasis classification; clinical T1cN0M0; tumor maximum diameter \>2 cm and \<=3 cm on imaging evaluation.
* Consolidation-to-tumor ratio (CTR) \>0.5 and \<=1 on thin-section computed tomography.
* Peripheral tumor judged by the investigator to be amenable to curative segmentectomy or lobectomy, with an anticipated ability to achieve the protocol-specified surgical margin.
* Eastern Cooperative Oncology Group (ECOG) performance status 0 to 1.
* Preoperative pulmonary function adequate for surgery, with forced expiratory volume in 1 second \>=60% predicted and single-breath diffusing capacity of the lung for carbon monoxide \>=60% predicted, unless otherwise documented after multidisciplinary evaluation.
* Willing to undergo intraoperative lymph node frozen-section biopsy to confirm node-negative status and understands that a positive frozen-section result will lead to conversion to lobectomy as standard treatment and exclusion from the primary efficacy analysis.
* Able to understand the study and voluntarily sign written informed consent.

Exclusion Criteria:

* Intraoperative lymph node frozen-section biopsy confirms N1 or N2 metastasis, or preoperative endobronchial ultrasound-guided biopsy or mediastinoscopy confirms N1, N2, or N3 metastasis, pleural dissemination, or distant metastasis. Patients with positive intraoperative frozen-section results will be converted to lobectomy plus systematic lymph node dissection as standard treatment and recorded as screen failures.
* Multiple primary lung cancers or multiple pulmonary nodules requiring concurrent resection outside the protocol-defined scope that would affect assessment of the primary endpoint.
* Prior ipsilateral lobectomy or segmentectomy, or severe pleural adhesions making the study procedure unevaluable.
* Other active malignancy within 5 years, except cured low-risk tumors.
* Severe cardiac, cerebral, hepatic, renal, or other disease that would preclude general anesthesia or curative lung cancer surgery.
* Pregnant or breastfeeding women.
* Any other condition that, in the investigator's opinion, makes the participant unsuitable for this study.