1. Colorectal cancer is one of the most common malignant tumors, and according to WHO 2012 data, the incidence of colorectal cancer ranks 3rd among male malignant tumors and 2nd among female malignant tumors. Liver metastasis is extremely common in colorectal cancer, with 20%-25% of patients having liver metastasis at the time of initial diagnosis; after radical resection of the primary site, the incidence of heterochronic liver metastasis reaches about 30%, i.e. about 50% of patients eventually develop liver metastasis in the course of colorectal cancer. 2. Liver metastases found at the time of diagnosis of colorectal cancer or occurring within 6 months after radical resection of the primary site of colorectal cancer are internationally defined as simultaneous liver metastases; liver metastases occurring after 6 months after radical resection of colorectal cancer are called heterochronic liver metastases (traditional standard). 3. The new concept of liver metastasis from colorectal cancer, simultaneous liver metastasis refers only to those metastases found at or before the diagnosis of the primary tumor in the intestine; all other metastases found after the diagnosis of the primary tumor are called heterochronic metastases, regardless of the time interval. All other metastases found after the diagnosis of the primary tumor, regardless of the time period, are referred to as heterochronous metastases. The risk of recent heterochronous metastases is relatively high and the prognosis is poor. 4. The concept of “oligometastasis” was first introduced in the 2015 ESMO Colorectal Cancer Guidelines to describe liver/lung metastases from colorectal cancer. The treatment goal is to achieve a tumor-free state with curative intent; the core principle of treatment is to emphasize local treatment on the basis of effective systemic treatment; the key is local treatment such as radiotherapy, surgery and radiofrequency ablation, while taking into account the prevention of distant metastasis. 5. Oligometastasis refers to an intermediate state in the process of tumor metastasis, which is a stage between the primary tumor and extensive metastases with mild biological aggressiveness, in which the primary tumor causes only a few local secondary metastases, usually ≤5 in number, representing a potentially curable state.