Lung cancer is classified according to the pathological staging criteria established by the World Health Organization, which contains a total of nine cell types, including: i. Squamous cell carcinoma. II. Small cell carcinoma. Adenocarcinoma. Large cell carcinoma. V. Adenosquamous carcinoma. Sarcomatoid carcinoma. Carcinoid tumor. Salivary gland type carcinoma. Unclassified carcinoma. In actual clinical work, because the biological behavior, treatment and prognosis of small cell carcinoma are very different from other types, sometimes lung cancer is generally divided into two types: small cell carcinoma and non-small cell lung cancer. Among these cell types, the more common are squamous cell carcinoma, small cell carcinoma, adenocarcinoma, and large cell carcinoma.