Stage III cancer means that the clinical staging of malignant tumor patients is in stage III, which belongs to the middle and late stages of malignant tumors, and requires specialists to choose appropriate diagnostic and treatment plans for treatment according to the actual situation of patients. At present, the staging principle of most cancers is TNM staging, according to the size of the tumor invading vital organs, organs, blood vessels, nerves can be divided into T1, T2, T3, T4 stage, T staging is mainly related to the depth of infiltration. Secondly, the lymph node metastasis stage is N. If there is no lymph node metastasis, it is N0; if there is metastasis, it can be divided into N1, N2 and N3 according to the number of proximal or distant metastasis. Finally, the M stage is whether there is bloodway metastasis to distant organs, if there is no metastatic organ metastasis, it is M0 stage, and if there is distant organ metastasis, it is M1 stage. After the above TNM staging can determine the clinical staging of malignant tumors, respectively, stage I, II, III, IV, and in this way to choose the best diagnostic and therapeutic modalities. The treatment modality for stage III cancer cannot be generalized, but needs to be judged according to the type of tumor, preferred treatment options, etc. Most malignant tumors at stage III require adjuvant radiotherapy to reduce the extent of tumor lesions and reduce lymph node and distant organ metastases. Only a few patients can choose radiotherapy followed by surgery. Therefore, specific treatment modalities for patients with stage III cancer need to be comprehensively evaluated and formulated by a specialist. It is recommended that patients with different types of tumors go to regular hospitals in time and follow the diagnostic and therapeutic advice of the corresponding specialists for treatment.