Lung cancer is divided into small cell lung cancer and non-small cell lung cancer, and non-small cell lung cancer is divided into squamous carcinoma, adenocarcinoma, and large cell carcinoma. Among them, the most powerful one is small cell lung cancer, because this type of lung cancer can develop distant metastasis in early stage, such as brain metastasis, bone metastasis, liver metastasis, adrenal metastasis, intrapulmonary metastasis, etc. Some patients come to the clinic because of the symptoms of brain metastasis and bone metastasis. Small cell lung cancer is highly malignant and relatively few drugs are available for treatment, especially in extensive stage small cell lung cancer, which cannot be operated, radiotherapy is also very difficult, and if the first-line chemotherapy regimen is not effective, the second- and third-line efficacy is even worse, and the side effects are also very large, and there are no corresponding targeted drugs or immune drugs, so the prognosis of small cell lung cancer is the worst.