Small cell lung cancer is a type of lung cancer, in which small cell lung cancer is categorized into limited stage and extensive stage. Extensive stage means that there are multiple metastatic foci in the lungs, metastasis to the lymph nodes or has been widely metastasized to other parts of the lungs, and the scope of invasion is relatively large. Small cell lung cancer is a lowly differentiated neuroendocrine tumor with small, round or ovoid cancer cells, unclear cell margins and less cytoplasm. Small cell lung cancer proliferates faster and is mainly characterized by early and extensive metastasis. Some data show that at the time of initial diagnosis, 60%~88% of patients have already developed brain metastasis, liver metastasis, bone metastasis, etc. The proportion of patients with extensive stage is higher and the prognosis is worse. The treatment of extensive stage of small cell lung cancer can take radiotherapy and chemotherapy, which are relatively more sensitive and can have better therapeutic effect.