The definition of cancer that has metastasized in the liver away from the primary cancer site is called hepatic metastatic cancer (tumor). Since the liver receives double blood supply from hepatic artery and portal vein, the blood flow is abnormally rich, and most of the malignant tumors from all organs of the body can metastasize to the liver. Malignant tumors in the gastrointestinal tract and pelvis can metastasize to the liver, among which the metastasis rate is higher for gastrointestinal tumors (gallbladder cancer, colorectal cancer, gastric cancer and pancreatic cancer, in that order), followed by chest tumors (lung cancer and esophageal cancer), breast cancer, hematologic tumors and some other types of tumors. All malignant tumors whose blood flows into the portal system, such as lower esophagus, stomach, small intestine, colorectum, pancreas, gallbladder and spleen, can metastasize to the liver through the portal vein, which is an important way for the primary cancer to spread to the liver. It has been reported that there is a diversion phenomenon of portal vein blood flow, that is, the blood flow from splenic vein and inferior mesenteric vein mainly enters the left liver, while the blood flow from superior mesenteric vein mainly converges to the right liver, and the tumors of these organs belonging to portal vein will metastasize to the corresponding parts of the liver due to different blood flow directions. However, clinically this shunting of tumor metastasis is not obvious, and instead, whole liver scattered metastasis is more common. Other tumors in the uterus, ovaries, prostate, bladder and retroperitoneal tissues may also metastasize to the liver through the anastomotic branches of the body vein or portal vein; or the tumors in these areas may grow to invade the organs of the portal vein system and then metastasize to the liver; or first from the body vein to the lung, and then from the lung to the systemic circulation and to the liver. 2.Hepatic artery metastasis Any hematologically disseminated cancer can metastasize to liver via hepatic artery, such as malignant tumors in lung, kidney, breast, adrenal gland, thyroid, testis, ovary, nasopharynx, skin and eye can be disseminated to liver via hepatic artery. Metastasis to the liver is also common. 3.Lymphatic metastasis of pelvic or retroperitoneal tumors can be spread via lymphatic vessels to the para-aortic and retroperitoneal lymph nodes, and then backflow to the liver. Cancer of the digestive tract can also metastasize retrogradely to the liver via the hilar lymph nodes via lymphatic vessels. Breast or lung cancer can also metastasize retrogradely to the liver via mediastinal lymph nodes, but this is a less common form of metastasis. More commonly, gallbladder cancer metastasizes to the liver along the lymphatic ducts of the gallbladder fossa. 4.Direct infiltration Cancer of adjacent organs of liver, such as gastric cancer, transverse colon cancer, gallbladder cancer and pancreatic cancer, can spread to liver by direct infiltration of cancer cells due to adhesion between cancer and liver, and cancer of the right kidney and adrenal gland can also directly invade liver. Diagnostic tests: Serological examination 1) Liver enzyme profile: For small metastases in liver, biochemical indexes can be completely normal. Most patients with liver metastases have normal liver function tests. Advanced patients or some patients can have elevated serum bilirubin, alkaline phosphatase, lactate dehydrogenase, γ-GT, etc. Abnormal coagulation and decreased albumin suggest extensive liver metastasis. When serum bilirubin is not high or bone metastasis is excluded, elevated AKP has reference value for the diagnosis of liver metastasis cancer. 2) CEA: The detection of serum CEA in patients with gastrointestinal tumors, especially colorectal cancer, is very important for monitoring the occurrence of liver metastases after surgery, and the sensitivity can reach 84-93%. Imaging examination 1) Ultrasound: B ultrasound is currently the preferred method for screening, follow-up and screening of liver metastases, and can detect lesions with a diameter of about 1-50px. Ultrasound of metastatic liver cancer can be shown as anechoic, hypoechoic, hyperechoic, “bull’s eye sign” and “target sign”. Intraoperative ultrasound: it can reduce interference and significantly improve the accuracy and resolution of diagnosis. 2) CT: It is a more accurate method to diagnose liver metastases, the advantage of CT is that the scan section is fixed, dynamic comparison can be made in lesion observation, which is more objective and more sensitive than ultrasound, the disadvantage of CT is that the specificity is poor, the sensitivity is not good for small nodules, diffuse and microscopic cancer foci, and some cases may be missed. 3) MRI: the sensitivity of diagnosing metastatic liver cancer is 64-100%, and it can distinguish lesions smaller than 25px, and it is better for clarifying the structure of tumor and adjacent blood vessels, with the advantages of high contrast of soft tissue, no radiation exposure and no contrast agent. 3.Other methods include nuclear medicine examination (PET, PET-CT, etc.), laparoscopic exploration, and intraoperative manipulative examination. The main purpose of clinical staging of liver metastatic cancer is to help formulate surgical treatment plan and evaluate prognosis. Some scholars in China have proposed the clinical staging of metastatic liver cancer to formulate surgical treatment plans and assess prognosis. This staging method roughly divides metastatic liver cancer into three stages: clinical stage I: hepatic solitary or <3< span=""> egg multiple metastatic cancer nodules that can be completely resected by hepatic resection within half the liver, radical hepatectomy can be performed in this stage, which has a greater chance of cure; clinical stage II: Those who can obtain complete resection with limited multiple scattered liver metastases and >3 multiple liver metastases through irregular hepatectomy in more than two non-same liver lobes and can complete resection of metastatic cancer through hemihepatectomy, the 5-year survival rate after this stage can reach about 20%. Clinical stage III (equivalent to advanced stage of primary cancer): regardless of single multiple metastases and those with extrahepatic metastases, it is difficult to remove liver metastases through surgery, and the median survival of this stage is about half a year. Treatment of metastatic liver cancer is different from that of primary liver cancer. Although the tumors both grow on the liver, the biological activity of liver metastatic cancer is the same as that of the tumor at the primary site, while it is very different from that of primary liver cancer. Therefore, first of all, it is necessary to clarify which organ or tissue origin of the primary cancer (taken to the pathology), and then mostly use systemic treatment (choose the plan according to the pathology of the primary cancer) + local interventional treatment of the liver.