The liver is one of the most common sites of metastasis in colorectal cancer, and 50%-60% of colorectal cancer patients eventually develop liver metastases, of which about 15%-25% are concurrent liver metastases and 22%-50% are heterochronic liver metastases [1]. The median survival time for patients with colorectal liver metastases (CRLM) who fail to obtain treatment is only 5 to 12 months. In contrast, the 5-year survival rate after obtaining radical resection for liver metastases can be 40%-58% [2], unfortunately, less than 10% of patients have obtained radical liver resection in clinical practice. In recent years, with advances in surgical techniques, imaging and systemic chemotherapy, more and more patients are being offered radical surgery. Since the location and number of liver metastases vary greatly, their sensitivity to chemotherapy varies, and they may be concurrent or heterochronic metastases; therefore, appropriate therapeutic measures need to be taken in the clinical setting depending on the condition. I. Surgical treatment of resectable CRLM 1. Definition of “resectable” criteria: Surgery is the best method for the eradication of CRLM. With the emergence of new chemotherapeutic drugs and advances in surgical techniques, the criteria for which patients are suitable for surgical resection have been constantly evolving. The current consensus is that the primary colorectal cancer lesion and liver metastases can be resected radically (R0 resection), sufficient residual liver function (residual liver volume ≥ 30%-50%) is preserved, and the patient’s general condition can tolerate the surgery is a sufficient condition for “resectable”. The size, number, location and distribution of liver metastases are no longer decisive factors in determining whether radical resection can be performed. Notably, patients with expected margins of less than 1 cm who also have hilar lymph node metastases or extrahepatic resectable metastases (e.g., pulmonary or abdominal metastases) have traditionally been considered “unresectable”. However, recent studies have shown that although the expected margin is less than 1 cm, as long as the microscopic margin is negative, the prognosis is still similar to that of patients with a margin of more than 1 cm [3]; for those patients with concomitant hilar lymph node metastases, Jaeck et al [4] showed a 5-year survival rate of 38% with concomitant hilar lymph node dissection during hepatic resection; Elias et al [5 ] reported a 5-year survival rate of 29% with radical resection of extrahepatic pulmonary metastases in conjunction with hepatic resection. Therefore, for this type of patients, a comprehensive analysis of the patient’s systemic condition should be performed and a prudent “individualized” treatment plan should be formulated, rather than rashly defining them as “unresectable”. 2. Surgical treatment of resectable simultaneous CRLM: For the surgical treatment of colorectal cancer diagnosed with liver metastases, it is still controversial whether the primary foci and liver metastases should be resected simultaneously in stage I or in stage II [6-7]. Traditionally, the primary lesion in the colorectum is resected first, and then the liver metastases are resected in the second stage. Studies have shown that postoperative complications are significantly lower with stage II staged resection than with stage I resection, especially for patients older than 80 years; they also receive neoadjuvant radiotherapy prior to hepatic resection, which helps to reduce the postoperative recurrence rate. However, staged resection still has the following shortcomings: (1) liver metastases may progress while waiting for hepatectomy, resulting in “unresectable”; (2) cumulative hospitalization time is prolonged and hospitalization cost is increased; (3) multiple operations are more traumatic for patients. Although first-stage resection avoids these shortcomings, safe implementation still requires careful case selection and skilled surgical techniques for hepatic resection and radical colorectal cancer. The Gastrointestinal Surgery Group and Colorectal Surgery Group of the Chinese Society of Medical Surgery and the Colorectal Cancer Committee of the Chinese Anti-Cancer Association jointly sponsored the Draft Guidelines for the Diagnosis and Comprehensive Treatment of Liver Metastases from Colorectal Cancer [8], which recommended simultaneous one-stage resection for patients who meet the following criteria: (i) the primary lesion of colorectal cancer can be radically resected; (ii) the liver metastases are small and mostly located in the periphery or confined to half of the liver, and the amount of liver resection (ii) the liver metastases are small and mostly located in the periphery or limited to the half of the liver, and the amount of liver resection is less than 50%; (iii) there are no other inoperable hilar lymph nodes, abdominal or distant metastases; (iv) the patient’s physical condition allows combined resection; (v) the operator is skilled in liver resection. The surgery can be performed in the same incision, extended incision or different incisions. With the increasing application of laparoscopic techniques in radical colorectal cancer and liver resection, it has become possible to complete the resection of primary foci and liver metastases in one stage under laparoscopy, so the surgical incision is no longer a prerequisite for performing stage one resection. It is worth emphasizing that in emergency situations, if the primary lesion is bleeding, perforated or obstructed, one-stage resection is not advisable; or if the extent of the resected liver is too large (e.g., hepatectomy of more than 3 liver segments), one-stage hepatectomy should also be carefully chosen. 3. Surgical treatment of resectable heterochronic CRLM: about 50% of colorectal cancer will develop liver metastasis after radical resection, therefore, regular postoperative follow-up is necessary. When metastases are found in the liver, further comprehensive and systematic examination should be performed to clarify whether the primary colorectal lesion is recurrent and whether there are other metastases outside the liver. Surgery should be performed for those who are judged to be suitable for surgery based on the above “resectable” criteria. The value of neoadjuvant chemotherapy in the treatment of resectable CRLM: There is no definitive answer as to whether resectable CRLM should be operated on directly or after neoadjuvant therapy. Several clinical studies have shown prolonged postoperative tumor-free survival and overall survival in patients receiving neoadjuvant therapy prior to liver resection compared to those undergoing direct surgery. Meanwhile, neoadjuvant chemotherapy can be used as a basis for evaluating the sensitivity of chemotherapy regimens and guiding the selection of postoperative chemotherapy regimens; Adam et al [9] also found that the 5-year survival rates after surgery were 8% and 37% in patients whose tumors still progressed after chemotherapy and in chemotherapy-sensitive patients, respectively. However, the disadvantages of neoadjuvant chemotherapy cannot be ignored, one is that liver injury due to chemotherapeutic drugs can increase the risk of surgery for subsequent hepatic resection. Currently, commonly used neoadjuvant drugs such as oxaliplatin can lead to hepatic sinusoidal injury and irinotecan can lead to hepatic steatosis. A randomized study by the European Organization for Research and Treatment of Cancer showed that the incidence of postoperative complications in the preoperative and postoperative groups receiving 6 cycles of FOLFOX4 chemotherapy and in the direct surgery group was 25.2% and 15.9%, respectively [10]. Secondly, some patients with completely disappeared lesions on imaging after receiving neoadjuvant chemotherapy could not be accurately located for resection intraoperatively, and these lesions may have residual cancer cells, which in turn become the main cause of postoperative recurrence. For these reasons, Chun et al [11] concluded that not all patients need to receive neoadjuvant chemotherapy, but only those with multiple metastases, which may also have occult lesions that cannot be revealed on imaging, need to receive neoadjuvant chemotherapy. For patients who have not received chemotherapy or received chemotherapy before 12 months of metastases discovery, preoperative chemotherapy for 2-3 months is recommended, and hepatic resection 4-6 weeks after the end of chemotherapy to help reduce the impact of chemotherapeutic liver damage on hepatic resection; for patients who have received chemotherapy within 12 months of discovery of liver metastases, direct surgical treatment is recommended. All patients should continue chemotherapy after surgery. II. Surgical treatment of unresectable CRLM Initially resectable CRLM cases are only about 10%; for cases with a large number of liver metastases initially unresectable, non-surgical treatments such as chemotherapy and radiotherapy are often used. In recent years, advances in surgical techniques, imaging and systemic chemotherapy have turned some of the initially unresectable cases into resectable ones, improving the prognosis of this group of patients. 1. Portal vein embolization: Since liver metastases are often multiple and located in different lobes of the liver, resection of all lesions often leads to postoperative liver failure due to insufficient residual liver volume. Therefore, accurate preoperative evaluation of the residual liver volume is particularly important. With advances in imaging technology, CT volume assessment is widely used to evaluate whether the expected residual liver is sufficient to maintain postoperative liver function. It has been found that the expected residual liver volume to whole liver volume ratio should be at least greater than 20% in patients with normal liver, at least greater than 30% in patients with chemotherapeutic liver injury, and at least greater than 40% in patients with comorbid chronic liver disease; also, in those patients with comorbid diabetes, high body mass index (BMI), and/or metabolic disorder syndrome, as it is often associated with liver In patients with diabetes mellitus, high body mass index (BMI) and/or metabolic disorder syndrome, more residual liver needs to be preserved during hepatectomy because of the reduced regenerative capacity of the liver due to steatosis. Portal vein branch embolization can lead to atrophy of the embolized lobe liver and compensatory hypertrophy of the non-embolized lobe liver volume. When the expected residual liver volume is insufficient, the portal vein to the branch of the proposed liver can be embolized preoperatively, and 3-4 weeks after embolization, compensatory hypertrophy will occur in the non-embolized lobe, i.e., the part of the liver expected to remain, and the hypertrophied liver may maintain the function of the postoperative residual liver, so that a part of inoperable patients The opportunity for surgery is obtained. For those patients with comorbid chronic liver disease, the waiting time for regeneration of the non-embolized liver lobe may be longer, taking 6 to 8 weeks. Several clinical studies have shown that portal vein branch embolization itself does not cause serious complications and that embolization can be performed after percutaneous transhepatic puncture of the portal vein branches or after a small incision in the right lower abdomen and placement of a tube through the ileocolic vein. 2. Two-stage hepatectomy: In some cases with multiple lesions distributed in the left and right hepatic hemispheres, all lesions cannot be resected in stage I. The small lesions present in the expected residual liver can be locally resected in stage I, followed by embolization of the portal vein branches. After 2-3 months, if there is no progression of the tumor and the expected volume of the residual liver after regeneration meets the requirements for safe hepatic resection, the embolized liver lobe can be removed in the second stage, thus achieving radical resection. Chemotherapy is routinely recommended between liver resections.Jaeck et al [12] reported a 3-year survival rate of 54% and a perioperative mortality rate of 0 in 25 patients who had routine staged resection of liver metastases, with complication rates of 15% and 56% between liver resections, respectively. Therefore, staged resection of liver metastases is feasible in some carefully selected cases and may improve the prognosis of patients. Hepatic resection after shrinking of liver metastases by chemotherapy: It has been shown that 14%-38% of patients with initially unresectable CRLM become suitable for radical hepatic resection after receiving neoadjuvant chemotherapy due to shrinking of liver metastases. CT liver volume assessment should be performed periodically during chemotherapy, and chemotherapy should be discontinued and hepatic resection performed as soon as the metastases shrink in size to the point where hepatic resection can be safely performed, because prolonged chemotherapy will increase the surgical risk of hepatic resection. Surgical resection: For most patients, surgical resection of liver metastases is the best means to obtain radical treatment. At least one of the three hepatic veins should be preserved after resection of liver metastases, and the volume of the residual liver should not be less than 50% in simultaneous hepatectomy and 30% in heterochronic hepatectomy. There is no definitive conclusion on whether to perform anatomic hepatectomy. It is generally believed that in order to preserve as much liver tissue as possible while performing radical resection, anatomical resection can be performed for large lesions, while non-anatomical resection can be performed for small lesions. 2. Ablation therapy: including radiofrequency ablation, microwave ablation and anhydrous ethanol ablation. Ablation therapy is often used in combination with surgery, for example, while removing large metastases in the right liver, ablation therapy is performed for small lesions located in the left liver parenchyma; or small lesions expected to remain in the liver are first treated by various ablation means, and then portal vein embolization is performed, and the embolized liver lobe is surgically removed after the liver has proliferated. Because of the possibility of residual tumor by various ablation means, it should be used with caution for lesions over 3 cm. In conclusion, with multidisciplinary involvement, the treatment of CRLM is increasingly enriched, but the ability to radically resect liver metastases is still an important factor affecting the prognosis of CRLM patients at present. Through multidisciplinary collaboration, increasing the radical resection rate of liver metastases in CRLM patients as much as possible can help improve the prognosis of such patients.