Liver metastasis is a common site for colorectal cancer to develop distant metastasis, and concurrent liver metastasis is defined as metastatic lesions appearing less than 6 months from the diagnosis of the primary tumor. The 5-year survival rate of patients with colorectal cancer liver metastasis (CRCLM) surgically resected at R0 is as high as 50%, while those who cannot be surgically resected are less than 10%. Evidence-based medicine has demonstrated that postoperative adjuvant chemotherapy can benefit patients with stage III and II disease with high-risk factors, and that adjuvant chemotherapy in the perioperative period is reasonable for CRCLM, which is stage IVa and surgical resection alone is clearly not sufficient. There are two treatment options for operable CRCLM: one is surgery followed by adjuvant chemotherapy, and the other is neoadjuvant chemotherapy followed by surgery followed by adjuvant chemotherapy. It is inconclusive which of these two treatment modalities will benefit the patient more. Evidence-based rationale for perioperative chemotherapy for CRCLM Recurrence or distant metastases after resection of liver metastases is a major cause of treatment failure, and about 70% of patients with CRCLM undergoing surgical resection alone will develop intrahepatic recurrence or distant metastases, mostly within 2 years after surgery. Two randomized controlled studies (FFCD/ACHBTH/AURC and EORTC/NCIC/CTG/GIVIO) compared the efficacy of adjuvant therapy after 5-Fu/LV compared with surgery alone, and the results showed that adjuvant chemotherapy was significantly more effective than surgery alone in both mPFS and mOS were significantly improved compared to surgery alone. However, a subsequent study found that the addition of irinotecan to 5-Fu/LV (FOLFIRI) regimen did not further improve outcomes. A phase III randomized controlled clinical study from Europe, the EORTC 40983 trial, compared the efficacy of surgical resection alone with perioperative chemotherapy (treatment with the FOLFOX4 regimen for 3 months preoperatively and postoperatively). The results showed that the 3-year recurrence-free survival rate was 9.2% higher in the perioperative chemotherapy group than in the surgery-only group (P=0.025). From the above clinical studies, it is suggested that either postoperative adjuvant chemotherapy or perioperative chemotherapy can improve the outcome of resectable CRCLM compared to surgical resection alone. Unfortunately, neither the previous studies nor the EORTC 40983 study established a comparison between the postoperative adjuvant chemotherapy group and the perioperative chemotherapy group, and it was not possible to determine that postoperative adjuvant chemotherapy was as effective as perioperative chemotherapy. In fact not all chemotherapy is effective, and for postoperative adjuvant chemotherapy, the effectiveness of chemotherapy cannot be verified because the tumor is resected; and concerns about preoperative chemotherapy due to liver injury causing adverse effects on surgery and ineffective chemotherapy causing tumor progression create concerns about preoperative chemotherapy. The survival advantage of prioritizing medical treatment is that preoperative chemotherapy (neoadjuvant chemo- therapy) for operable patients only aims to further improve the efficacy and reduce the difficulty of resection, but not to increase resectability, and the course of treatment is usually 2-3 months. Data show that in the past 10 years, the majority of clinical studies of neoadjuvant chemotherapy for resectable CRCLM have used a two-drug regimen based on 5-Fu combined with platinum oxalate or irinotecan, with an efficiency of 45% to 70%. Among them, CR can reach 4% to 10%. A meta-analysis of 23 clinical studies collecting 3278 patients suggested that neoadjuvant chemotherapy was 64% effective, suggesting that most patients with resectable CRCLM benefit from effective neoadjuvant chemotherapy, and that treatment effectiveness may be an important factor in survival benefit. control, had a higher 5-year survival rate than those who received direct surgery without neoadjuvant chemotherapy (85% vs 35%, P=0.03). The same results were obtained in the study by Adam et al. in France, where the 5-year postoperative survival rates were 37%, 30%, and 8% for those with effective (CR+PR) stable (SD) and progressive (PD) neoadjuvant chemotherapy, respectively, with significant differences (P<0.01). The study showed that those with effective neoadjuvant chemotherapy had better postoperative survival. The priority of internal medicine can provide a "biological waiting window". Doctors always strive for higher efficacy and take aggressive treatment measures for their patients. For example, if a patient is considered operable on the basis of preoperative imaging, but after opening the liver or abdomen is found to be covered with corn-like metastatic nodes, the surgery becomes a "switch operation". The other scenario is even more regrettable: the tumor recurs and progresses rapidly within a short period of time after resection, rendering the surgery worthless and leaving the patient more traumatized. If patients receive neoadjuvant chemotherapy as a priority for 2-3 months, it provides a "biological waiting window" for the tumor, and if treatment is ineffective, it can distinguish patients with poor prognosis and rapid progression to avoid unnecessary surgery. If the treatment is effective, it can eliminate the hidden lesions on imaging and avoid the "switch" procedure when unresectable microscopic lesions are found during direct surgery, which can turn potentially resectable lesions into unresectable ones. A 2010 Dutch study in Ann Oncol included 106 patients with stage II and 258 patients with stage III 5-Fu-based colorectal cancer treated with surgery alone, and the analysis showed that BRAF V600E mutation predicted poor prognosis in patients with stage II and III colon, and BRAF mutation independently predicted overall and tumor-specific survival (HR 0.45 and 0.47, respectively), independent of disease stage and treatment modality.Adam's study found that patients with disease progression during neoadjuvant chemotherapy, even if surgical resection was still possible, had a poor prognosis, with a 5-year survival rate of only 8%. The 5-year survival rate was only 8 percent. The prognosis was not better than that of inoperable patients. The safety impact of neoadjuvant chemotherapy on surgery is of greater concern to surgeons, who worry that preoperative chemotherapy will not only affect bone marrow function, suppress the body's immunity and tissue healing ability, and increase postoperative complications such as infection and bleeding, but also worry about chemotherapy-induced liver injury such as 5-FU-induced hepatic steatosis, oxaliplatin-induced blue liver (hepatic sinusoidal obstruction syndrome), and The results of the EORTC 40983 study found that in the neoadjuvant chemotherapy and direct surgery groups, the surgical complications were 25% and 16%, respectively, p=0.04, and most of these complications were reversible and did not increase the surgical mortality rate, which was 1 percent. Most previous clinical studies have found that the above specific liver injury caused by preoperative chemotherapy mostly occurs after more than 3 months of chemotherapy, and further studies have demonstrated that preoperative chemotherapy for more than 6 months only significantly increases the risk of surgical complications and mortality. Therefore, controlling the course of preoperative chemotherapy is the key to reduce chemotherapy-induced liver injury, and the guideline recommended preoperative chemotherapy course for operable CRCLM is 2-3 months, which is generally safe. CONCLUSION: The currently recommended chemotherapy regimen for preoperative neoadjuvant treatment of concurrent operable CRCLM with a 2-3 month course has a high remission rate and does not increase operative mortality, and is overall safe and effective. For the treatment of operable CRCLM, ESMO experts recommend: "neoadjuvant chemotherapy followed by surgical resection is recommended for more than one of the following factors: >3 metastases; tumors ≥5 cm in maximum longitude; metastases present <12 months after resection of the primary site (including concurrent liver metastases); primary site with lymph node metastases; CEA >200 ng/ml. Therefore, in the absence of new and more convincing evidence-based findings, ESMO expert guidelines are recommended for clinical treatment decisions.