Colorectal cancer is one of the common malignant tumors. At present, almost all hospitals above county level in China can carry out colorectal cancer surgery. However, we should recognize that the treatment of colorectal cancer in China, especially the surgery-based comprehensive treatment, is far from standardized, and surgeons in some primary hospitals have not mastered the basic treatment principles of colorectal cancer.In 2010, the Ministry of Health issued the “Chinese Colorectal Cancer Treatment Specification (2010 Edition)” [1], which is the first time since the founding of New China that the national competent department is responsible for compiling a clinical guideline specification for This is the first clinical guideline for a single disease compiled by a national authority since the founding of New China, and it plays an important guiding role and administrative restraint role in regulating the treatment behavior of colorectal cancer in China. The Ministry of Health requires medical institutions at all levels nationwide to implement the diagnosis and treatment of colorectal cancer in strict accordance with the requirements of the Code, and there is no doubt that the Code has positively promoted the improvement of the diagnosis and treatment of colorectal cancer in China. We found through many clinical research articles that surgeons, despite their very good clinical work, generally did not perform correct preoperative staging before colorectal cancer treatment. In today’s rapidly developing evidence-based medicine, the treatment of malignant tumors without preoperative clinical staging cannot guarantee the selection of the correct treatment method. Therefore, surgeons’ understanding of preoperative staging of colorectal cancer is a prerequisite for achieving standardized and comprehensive treatment of colorectal cancer. I. Significance of preoperative staging of colorectal cancer Treatment of colorectal cancer has made great progress in recent years due to the improvement of surgical techniques, new treatment methods, as well as the advancement of radiotherapy techniques, chemotherapy drugs and molecular targeted drugs. The emergence of multidisciplinary team (MDT) [2-3] has brought the treatment of colorectal cancer into the era of integrated multidisciplinary treatment. MDT is the first step in the treatment of colorectal cancer. The first step in colorectal cancer treatment is a comprehensive assessment of the patient including preoperative clinical staging. Clinical staging is a prerequisite for colorectal cancer treatment because there are significant differences in treatment approaches when we face colorectal cancer patients with different stages of disease. II. Preoperative TNM staging of colorectal cancer The selection of neoadjuvant treatment for colorectal cancer starts with the preoperative clinical assessment of patients. In China, most surgeons tend to use the traditional Dukes clinical staging system for colorectal cancer, while almost all international literature now adopts standardized TNM clinical staging, which is crucial to the comprehensive treatment of colorectal cancer. It should be noted that for rectal and colon cancers, there are major differences in their preoperative treatment principles, especially when clinical staging is different. For colon cancer, traditional CT examination plus colonoscopy can basically complete the clinical staging. However, the preoperative clinical staging of rectal cancer mainly relies on intraoperative transrectal endoscopic ultrasound (T-staging) and MRI for N-staging. Correct preoperative staging is an important prerequisite for neoadjuvant treatment of colorectal cancer. For preoperative evaluation we performed preoperative clinical staging of rectal cancer based on the TNM classification system of AJCC (Table 1, 2). III. Differences in preoperative staging of colon and rectal cancer The clinical staging method of colorectal cancer is consistent in the TNM staging method, but in fact there are differences in the anatomical structures of colon and rectum. The colonic mesentery is covered by plasma membrane, which is well defined clinically in the colon. However, the plasma membrane of the rectum is anatomically very different from that of the colon. From the classical anatomical distinction, the rectum is divided into 3 segments: upper, middle and lower. Therefore, the T4 stage (tumor invasion of the plasma layer) in the definition exists in the anterior part of the upper and middle rectum, but not in the lower rectum, and this detail should be clarified in future guidelines. Pre- and postoperative evaluation of TNM staging There is a difference between preoperative and postoperative staging and whether or not preoperative treatment is expressed on TNM staging. For preoperative staging of colon cancer, CT and ultrasonography are generally used for diagnosis. For unresectable lesions assessed preoperatively, the necessary preoperative treatment is performed. The preoperative clinical staging also refers to the TNM staging method, but due to the different methods of staging, the usual preoperative staging is indicated as cTNM (e.g. cTIN2bM0), which indicates the clinical staging; if the patient receives preoperative neoadjuvant therapy, including preoperative radiotherapy, the pathological evaluation obtained after surgery is ypTNM; for patients who do not receive neoadjuvant therapy, the pathological evaluation after surgery is pTNM The evaluation of recurrent colorectal cancer should be marked as rTNM, indicating recurrence. Some scholars have also labeled T-staging with transrectal endoscopy as uTNM.Figure 1 On high-quality postoperative specimens after total rectal mesenteric resection, differences in the anatomical structures of the upper and middle and lower rectum can be more easily recognized. In the middle and lower rectum, the plasma membrane structures gradually disappear and are replaced by a pelvic fascial dirty layer (ink-stained area). Therefore, there is no plasma membrane covered area, and according to the existing guidelines, there should be no sub-stage T4a V. TNM staging and treatment strategy selection for colorectal cancer (a) Preoperative evaluation and strategy of liver metastases from colorectal cancer Liver metastases from colorectal cancer are very common in clinical practice, and liver metastases occur in 20% to 50% of colorectal cancers, and the treatment strategy for the occurrence of liver metastases has changed dramatically in recent years [4]. For patients with suspected liver metastases, preoperative clinical staging is very important. Usually, patients with liver metastases from colorectal cancer are distinguished as resectable, potentially resectable, or unresectable. Resectable colorectal cancer liver metastases are usually surgically removed from both the primary site and liver metastases according to the patient’s condition. However, for patients with potentially resectable disease, preoperative neoadjuvant therapy is usually used to convert the liver lesions into resectable ones, followed by resection in one piece or in stages. For lesions in which the liver is unresectable, if there is no perforation, bleeding, or obstruction of the colorectum, medical treatment should be the mainstay [5]. (ii) Early resection of rectal cancer At present, there are many problems in the early resection of rectal cancer in China. They are mainly manifested in that surgeons in some places do not understand the principles of treatment for early rectal cancer and do not perform preoperative staging. For rectal cancer, early rectal cancer usually refers to patients with T1-T2 NO, which means the tumor only invades the mucosa or submucosa layer. Moreover, the indications for local resection of early rectal cancer are very strict, and according to the Chinese Colorectal Cancer Diagnostic and Treatment Standard (2010 edition) and the American NCCN clinical guidelines, for early rectal cancer, local resection can only be performed in patients with T1 stage, who also meet the requirements of tumor less than 8 cm from the anus, diameter less than 1/3 of the rectum, incisional margin greater than 3 mm, good differentiation, and no vascular nerve invasion [6]. Since some surgeons do not clinically stage patients with early local resection of rectal cancer, the selection of indications for this group of patients is more problematic. (iii) Inadequacy of neoadjuvant therapy for progressive rectal cancer For the treatment of progressive rectal cancer, preoperative neoadjuvant therapy port 1 should be used clinically, including preoperative radiochemotherapy or radiotherapy alone [7-12]. There has been a large amount of evidence-based medical evidence that preoperative neoadjuvant radiotherapy or preoperative radiotherapy alone should be done for progressive rectal cancer as long as it is in stage T3, regardless of the presence of lymph node metastasis [5]. Due to the differences in socioeconomic conditions in China and factors such as surgeons’ perceptions, preoperative neoadjuvant therapy has not been commonly carried out in China. (4) Treatment concept of locally advanced rectal cancer Locally advanced rectal cancer generally refers to stage T4, where the tumor has invaded the pelvic wall, forming a “frozen pelvis”; or the tumor has invaded the surrounding organs, which is mainly manifested in the clinical stage of T4b. For such patients, due to the difficulty of surgery, combined organ resection is often required, and most patients should undergo preoperative radiotherapy. Patients should undergo preoperative radiotherapy. The purpose of this treatment is to shrink the tumor through radiotherapy, and some patients can become resectable lesions. For patients for whom radiotherapy is ineffective and radical resection cannot be completed, sigmoidostomy can be considered and then the patient can receive radical radiotherapy. Preoperative staging of colorectal cancer is a basic skill that surgeons must master, especially they should closely track the trend of development and changes of colorectal cancer treatment at home and abroad, and guide clinical treatment in strict accordance with norms and guidelines in order to effectively improve the treatment level of colorectal cancer in China, so that the limited medical resources can play the greatest role for the benefit of colorectal cancer patients.