Megestrol Acetate for First-Line Treatment of Malnourished Non-Small Cell Lung Cancer

Inclusion Criteria: * Voluntarily provide written informed consent (ICF). * Age ≥18 years at enrollment. * Eastern Cooperative Oncology Group (ECOG) performance status score of 0-1. * Expected survival ≥6 months. * According to the 8th edition of the Lung Cancer TNM Staging Classification by the International Association for the Study of Lung Cancer (IASLC) and the American Joint Committee on Cancer (AJCC), subjects have histologically or cytologically confirmed locally advanced (Stage ⅢB/ⅢC) or metastatic (Stage IV) NSCLC that cannot be completely resected by surgery and cannot receive radical concurrent/sequential chemoradiotherapy. * Subjects have not received systemic chemotherapy for locally advanced or metastatic NSCLC before. For patients who have previously received adjuvant chemotherapy/radiotherapy, neoadjuvant chemotherapy/radiotherapy for non-metastatic diseases with curative intent, or radical chemoradiotherapy for locally advanced diseases, they are eligible to participate in this study if disease progression occurs more than 6 months after the end of the last treatment. * Subjects who have previously received PD-1/L1 inhibitors in the neoadjuvant phase are allowed to participate in this study after evaluation and approval by the investigator; subjects who have previously received PD-1/L1 inhibitors in the adjuvant phase or the consolidation treatment phase after radical chemoradiotherapy are not allowed to participate in this study. * No EGFR sensitive mutation or ALK gene translocation. For squamous NSCLC subjects with a smoking history or current smoking, if the previous EGFR and ALK status is unknown, it is considered negative. * Body mass index (BMI) ≤ 25. * At least one measurable tumor lesion according to RECIST v1.1. Exclusion Criteria: * Diagnosis of NSCLC with EGFR sensitive mutation or ALK gene translocation; subjects with small cell carcinoma components in histology. * Presence of any condition affecting gastrointestinal absorption, such as difficulty swallowing, malabsorption, or uncontrollable vomiting; currently receiving tube feeding or parenteral nutrition; suffering from anorexia due to neurological or psychiatric disorders, or difficulty eating due to pain. * Currently taking or planning to take other medications that increase appetite or body weight, such as corticosteroids (excluding short-term dexamethasone during chemotherapy), androgens, progestins, thalidomide, olanzapine, anamorelin, or other appetite stimulants. * Patients with Cushing's syndrome, adrenal or pituitary insufficiency; patients with poorly controlled diabetes. * Postmenopausal women with a history of abnormal vaginal bleeding within one year; premenopausal women with a history of abnormal endometrial thickening (\>15 mm) within one year. * Current radiological or clinical evidence of gastrointestinal obstruction.