Thrombosis of portal vein trunk in liver cancer is a manifestation of liver cancer progression, which is a manifestation of relatively advanced stage of liver cancer, and the main causes of the corresponding condition include direct invasion of portal vein and portal vein reflux. 1. Direct invasion of portal vein: with the gradual increase of tumor volume, it will invade the surrounding tissues, and the tumor will directly invade the main stem of portal vein and form tumor tissues in the portal vein, which is a form of cancerous thrombosis. 2. Portal vein reflux: it will cause portal vein reflux, which will further lead to tumor cells entering into the portal vein trunk, causing the formation and enlargement of cancer thrombus. When cancerous thrombus formation of portal vein trunk is found in liver cancer, it should be hospitalized in time and treated in a standardized way under the guidance of clinicians, so as to avoid seriousness of the condition.