This study is a prospective, randomized, parallel-controlled clinical trial, primarily aimed at evaluating the efficacy and safety of Nanocrystalline Megestrol Acetate combined with standard therapy, compared with placebo combined with standard therapy, in improving appetite and body weight during concurrent chemoradiotherapy for patients with locally advanced non-small cell lung cancer.

Inclusion Criteria:

1. Voluntarily provide written informed consent (ICF).
2. Age ≥ 18 years at enrollment.
3. Eastern Cooperative Oncology Group (ECOG) performance status score of 0-2.
4. Expected survival ≥ 6 months.
5. Histologically or cytologically confirmed, unresectable or inoperable locally advanced (stage III) non-small cell lung cancer (adenocarcinoma or squamous cell carcinoma) according to the 8th edition of the TNM classification by the International Association for the Study of Lung Cancer (IASLC) and the American Joint Committee on Cancer (AJCC).
6. Planned to receive radical concurrent chemoradiotherapy.
7. Body mass index (BMI) ≤ 25.
8. At least one measurable tumor lesion according to RECIST v1.1.

Exclusion Criteria:

1. 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.
2. 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.
3. Patients with Cushing's syndrome, adrenal or pituitary insufficiency; patients with poorly controlled diabetes.
4. 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.
5. Current radiological or clinical evidence of gastrointestinal obstruction.