Adenocarcinoma can be divided into adenocarcinoma, squamous carcinoma and undifferentiated carcinoma. Adenocarcinoma originates from columnar epithelium and glandular epithelium, according to the size of cancer cells, adenocarcinoma can be divided into two types, highly differentiated adenocarcinoma and poorly differentiated adenocarcinoma. Squamous carcinoma originates from squamous epithelium. According to the degree of differentiation of cancer cells, squamous carcinoma can be divided into highly differentiated keratinized squamous carcinoma and poorly differentiated non-keratinized squamous carcinoma, and the well-differentiated one is highly differentiated keratinized squamous carcinoma, so its prognosis is also better. Undifferentiated carcinoma, also known as small cell undifferentiated carcinoma, generally originates from silver-loving cells in the bronchial epithelium, which can produce peptide hormones and cause endocrine symptoms, and therefore belongs to neuroendocrine tumors. Undifferentiated carcinoma is characterized by small, round, and less nucleated cells, and the prognosis of undifferentiated carcinoma is poor.