Chemotherapy is necessary to treat a cancerous embolus in the vasculature, which mainly refers to the blood vessels and lymphatic vessels. If there is already a cancer thrombus in the vasculature, it means that the cancer cells may metastasize to other distant parts of the body through blood vessels and lymphatic vessels. Therefore, even after surgical resection, postoperative adjuvant chemotherapy is needed in this case. Postoperative adjuvant chemotherapy can reduce the chance of recurrence and metastasis in the future. Even if the tumor is very early at the time of resection, as long as there is a poor prognostic factor of vascular thrombus, postoperative adjuvant chemotherapy is still needed. Some experts even believe that the risk of seeing a cancerous thrombus in the vasculature is higher than that of regional lymph node metastasis, so chemotherapy is necessary for seeing a cancerous thrombus in the vasculature.