Current status of liver metastasis from colorectal cancer The liver is the most important site of metastasis from colorectal cancer, with a high incidence of 50%. Colorectal cancer liver metastasis is a very complex biological process, and the mechanism is not fully understood, and micrometastasis is one of the possible causes. From the anatomical point of view, the venous blood flow draining the colorectum converges into the portal vein into the liver. The hepatic sinus is the site of blood return from the gastrointestinal tract, which has a high contouring rate to the blood flow and is the organ where the tumor cells are most likely to settle; colorectal cancer is most likely to invade the vein. Once cancer cells are shed into the blood circulation, it is easy to form metastases in the liver. Liver is the most common metastatic organ of malignant tumor, according to foreign autopsy data: 40% of malignant tumor patients have liver metastasis, while the rate of liver metastasis of colorectal cancer patients is as high as 60%-71%. Colorectal cancer liver metastasis is divided into simultaneous liver metastasis and heterochronic liver metastasis. In the former case, liver metastasis is found at the same time when colorectal cancer is discovered, and the interval between the discovery of primary and liver metastases is < 6 months; in the case of liver metastasis after colorectal cancer surgery, the interval between the discovery of primary and liver metastases is > 6 months, which is called heterochronic liver metastasis, and about 30%-40% of heterochronic liver metastases occur after the so-called radical resection, and 80% occur within 2 years after surgery. Liver metastasis is the main reason affecting the prognosis and long-term survival of colorectal cancer. Pay attention to liver metastasis of colorectal cancer For patients with colorectal cancer, doctors should consider the possibility of liver metastasis and routinely perform liver ultrasound, CT and other related examinations before surgery. The liver should be routinely explored during surgery, and intraoperative ultrasound examination can be considered if necessary. Patients should be followed up after treatment, once every 3-6 months for 1 to 2 years after surgery; once every 6-12 months for 3 to 5 years after surgery; once every 1 to 2 years after 5 years. The follow-up items include tumor marker (CA199, CEA) test, ultrasound, CT and chest X-ray, etc. Surgical patients should have regular colonoscopy to detect recurrence of anastomosis and other parts of the colon. Measures to prevent liver metastasis of colorectal cancer: pay attention to the principle of tumor-free operation, avoid squeezing the tumor by gentle movements, and tie the tumor with cloth bands on both sides of the tumor cut edge; resect the intestinal canal and clear the lymph nodes according to the principle of radical treatment to achieve the degree of radical treatment; adopt intraoperative portal vein or hepatic artery placement, and continuous postoperative 5-FU chemotherapy; formulate reasonable postoperative adjuvant treatment plan according to the pathological results and follow up closely. The treatment should be based on the pathological results and followed up closely. Actively deal with colorectal cancer liver metastasis Traditionally, it is believed that colorectal cancer liver metastasis is clinical stage IV, which has lost the significance of treatment, thus depriving patients of the opportunity of treatment. With the advancement of imaging technology, early, isolated and smaller metastases can be detected; the improvement of surgery, anesthesia and perioperative treatment level has greatly reduced the complications and mortality of surgery; the adjuvant treatment based on neoadjuvant chemotherapy can reduce the clinical stage of patients and can transform inoperable tumors into resectable tumors. The treatment of colorectal cancer liver metastasis can be divided into: surgical treatment and non-surgical treatment, the latter including: systemic chemotherapy, trans-portal chemotherapy, trans-hepatic artery embolization chemotherapy, etc. Surgical resection is still the preferred treatment for colorectal cancer liver metastases. For the treatment of simultaneous liver metastases: (1) The primary foci can be resected and liver metastases can also be resected, and the primary foci and metastases should be resected at the first stage. (2) If the primary foci can be resected but the metastases cannot be resected, resection of the primary foci, portal vein and hepatic artery placement, postoperative chemotherapy via portal vein + hepatic artery embolization + systemic chemotherapy should be performed. (3) If both primary and metastatic foci are unresectable, palliative surgery is performed as appropriate. These include short-circuit surgery and stoma, etc., with postoperative adjuvant chemotherapy. For the treatment of heterochronic liver metastases, i.e. liver metastases that appear after the primary foci have been resected: (1) if the liver metastases can be resected, the tumor can be surgically removed; (2) if the liver metastases cannot be resected, local treatment such as TACE, radiofrequency, cryotherapy and other comprehensive measures such as systemic chemotherapy are feasible. It is generally believed that the later the liver metastasis occurs after the first primary site is removed, the better the prognosis. A comprehensive and detailed systemic examination should be performed before liver resection surgery to exclude metastases from other sites. Irregular hepatectomy is recommended. Adjuvant comprehensive treatment should be added after surgery. For liver metastases that appear within a short period of time (within 1 year after surgery) after colon cancer surgery, even if the metastases can be resected, 1 to 2 cycles of systemic chemotherapy should be administered before irregular liver resection. The most important factor in determining the resectability and prognosis of liver metastases is the number of metastases, i.e., the “metastatic burden”. In a small proportion of patients with liver metastases that are confined to one lobe or segment, surgical resection is not only simple, but also has a 5-year survival rate of 50%. The choice of the surgical indication and the surgeon’s experience are key factors in determining the surgery. Factors affecting the surgical resection of liver metastases include poorly differentiated tumor, metastasis to abdominal lymph nodes, metastasis to extrahepatic organs, unclear surgical margins, and metastasis to both lobes of the liver. Clinical studies have confirmed that neoadjuvant chemotherapy can give some unresectable colorectal liver metastases a chance of surgical resection. The 5-year survival rate for colorectal cancer liver metastases treated with FOLFOX (platinum oxalate, calcium folinic acid, 5-FU) after a three-week regimen of chemotherapy was 40%. For unresectable colorectal cancer with liver metastases, the main chemotherapy regimen is 5-FU continuous intravenous drip, calcium folinic acid biochemical modulator, combined or alternated with platinum oxalate and irinotecan. Chemotherapy can be combined with targeted therapies such as bevacizumab (Avastin, anti-tumor angiogenesis) and cetuximab (C-225, anti-epidermal growth factor receptor). The value of surgical treatment of colorectal cancer liver metastases The 5-year and 10-year survival rates and surgical mortality rates after surgery for colorectal cancer liver metastases can reach 50% and 30%, respectively. With the improvement of surgical techniques for liver resection (e.g. resection of mid-hepatic tumors and tumors near the hilum) and the development of related disciplines (advanced liver resection equipment and effective drug therapy), surgical procedures previously considered inappropriate have become safe and the indications for surgery have been expanded, with a 5-year survival rate of 50%. Liver metastasis of colorectal cancer is a problem worthy of great attention in the diagnosis and treatment of colorectal cancer patients, and timely diagnosis and reasonable treatment can significantly prolong the survival and improve the prognosis of patients.