The most important thing to judge the stage of lung cancer is from 3 aspects: 1) the size and number of lung tumor itself; 2) the presence or absence of lymph node metastasis, as well as the number and location of lymph node metastasis; 3) the presence or absence of distant metastasis, including distant organ metastasis and malignant pleural fluid from pleural metastasis. If the tumor is very large, for example, more than 7cm, it has invaded the local chest wall and is already locally advanced. If there are also lymph nodes, especially lymph nodes in the mediastinum or even lymph nodes in the contralateral lung, it is also in the locally advanced stage. If there is also malignant pleural fluid, bone metastasis, brain metastasis, such as severe headache, pain in many places of the body, and metastasis of internal organs, it is already in the most advanced stage. The main way to determine whether there are metastases in these areas is to rely on imaging tests, such as CT and MRI.