Lung cancer is divided into small cell lung cancer (about 20%) and non-small cell lung cancer (about 80%) according to the pathology. Non-small cell lung cancer is mainly divided into squamous cell carcinoma (about 40% of lung cancer), adenocarcinoma (about 20-30%) and large cell lung cancer (about 15%). Large cell lung cancer, also called undifferentiated large cell lung cancer, is a type of undifferentiated epithelial cell carcinoma that lacks the cellular differentiation characteristics of small cell lung cancer, adenocarcinoma or squamous cell carcinoma. It is divided into: (1) large cell neuroendocrine lung cancer (2) basal cell-like carcinoma (3) lymphoepithelial-like carcinoma (4) clear cell carcinoma.