Whether lung adenocarcinoma 3~4 cm is serious or not also depends on the scope of primary tumor invasion, local lymph node metastasis, the presence of distant metastasis, the patient’s physical condition and other factors. Lung adenocarcinoma is a type of non-small cell lung cancer, most of which originates from the epithelial cells of bronchial mucosa, and a small portion of which originates from the mucous glands of the large bronchial tubes. In clinic, whether lung adenocarcinoma is in early or late stage is determined according to three aspects: primary lesion of lung adenocarcinoma, local lymph node metastasis and whether distant metastasis occurs. 1. Scope of invasion of primary tumor: 3~4 cm of lung adenocarcinoma indicates that the local lesion is large. If the tumor is confined to the lung and has not invaded the pleura and other surrounding tissues and organs, the prognosis is better. If the tumor has involved the pleura, or has invaded the mediastinum or heart, the prognosis is worse. 2. Local lymph node metastasis: the prognosis is better if the local lymph node metastasis is small and limited. Some patients with contralateral hilar, mediastinal or oblique muscle or supraclavicular lymph node metastasis have a poorer prognosis. 3. Distant metastasis: when lung adenocarcinoma has distant organ metastasis, such as brain metastasis and liver metastasis, it means that it is already in the advanced stage, and the prognosis of the patients at this time is worse than that of those who do not have distant metastasis. 4. Physical condition of patients: Treatment of lung adenocarcinoma includes surgery, chemotherapy, radiotherapy, immunotherapy and targeted drug therapy. Patients with poor physical condition, who cannot bear standardized treatment plan, have poorer prognosis. Therefore, whether lung adenocarcinoma 3~4 cm is serious or not needs to refer to many factors. It is recommended to consult medical oncology in time, and decide the specific treatment plan after the doctor comprehensively evaluates the condition.