(1) Small cell carcinoma: It is a highly malignant tumor with rapid growth and early metastasis. The cancer cells are small, spindle-shaped or lymphocyte-like, similar to small lymphocytes, and shaped like oat grains, thus also called oat cell carcinoma. They have little cytoplasm, naked nucleus, deep staining, and contain neuroendocrine granules in the cytoplasm, which is a kind of low differentiated neuroendocrine carcinoma. The incidence rate is lower than that of squamous carcinoma, and the age of onset is younger, mostly seen in men. It usually originates from larger bronchi, and most of them are central type lung cancer. Small cell carcinoma is highly malignant, fast-growing, and has early lymphatic and hematologic metastases. Although it is more sensitive to radiation and chemotherapy, it has a poorer prognosis among all types of lung cancer. (2) Squamous cell carcinoma: Most of the patients are over 50 years old, and most of them are male, with a history of smoking. Most of them are central type lung cancer. The histology of squamous cell carcinoma can be divided into three types: highly differentiated, moderately differentiated, and poorly differentiated, with different degrees of differentiation, slow growth rate and longer disease duration compared with other types of lung cancer, and more sensitive to radiation and chemotherapy. It is more sensitive to radiation and chemotherapy. It usually metastasizes via lymphatic metastasis and bloodstream metastasis occurs later. (3) Adenocarcinoma: It develops at a younger age and is relatively common in women. It is mostly peripheral type lung cancer, with a few originating from large bronchi. It is often detected on chest X-ray and appears as a round or oval lobulated mass, which often involves the pleura. The histology is similar to that of adenocarcinoma in other areas. The growth is usually slow, but sometimes bloodstream metastasis occurs at an early stage. (4) Large cell carcinoma: Very rare, about half of them originate from large bronchi. The cancer cells are large in size, with abundant cytoplasm, obvious nucleoli, large nuclei, many nuclear schisms, and obvious heterogeneity, and many multinucleated tumor giant cells are common. Large cell carcinoma has low differentiation, high malignancy, rapid growth, and poor prognosis.