Colorectal cancer is a common tumor, including colon cancer and rectal cancer. The incidence rate of colorectal cancer accounts for about 10%-15% of all tumors and is the second most common cancer death in western countries and the fifth in China. According to the epidemiological data of tumors in Shanghai, colorectal cancer is on the rise in China, and its incidence rate is increasing year by year, more rapidly in big cities. Due to its special anatomical location and close relationship with surrounding tissues, rectal cancer, especially lower and middle rectal cancer, is more difficult to be treated surgically, with more complications, more common functional damage, and higher local recurrence rate with simple surgical treatment, so the treatment effect is not satisfactory. With the progress of science and technology, the emergence of new diagnostic and therapeutic means, including the application of magnetic resonance examination for precise preoperative staging of rectal cancer patients, the development of new chemical drugs and targeted drugs, the development of new three-dimensional conformal radiotherapy technology, the advancement of surgical anastomosis technology and minimally invasive surgery technology, have led to a great development in the treatment of colorectal cancer, and the therapeutic effect has also been improved to different degrees. 1. Full understanding of the importance of preoperative staging of rectal cancer In formulating a multidisciplinary comprehensive treatment plan for rectal cancer, medical imaging experts are needed to make reasonable preoperative assessment of patients, provide relevant information on the depth of tumor invasion into the intestinal wall, local lymph node metastasis and distant metastasis through relevant examinations, perform preoperative staging, decide the application of neoadjuvant therapy and select suitable patients to receive local resection. Currently whether preoperative staging of rectal cancer is routinely performed is an important indication of the level of treatment. Commonly used preoperative staging methods include rectal endoscopic ultrasound, spiral CT scan, rectal MRI and PET/CT. preoperative staging usually adopts the international common clinical TNM staging. 2.Adjuvant chemotherapy after colon cancer surgery needs to master the indications In 1990, it was proved that 5FU-based adjuvant chemotherapy for colon cancer is superior to surgery alone, which opened the era of adjuvant chemotherapy FU for colon cancer, and after about 15 years of slow research progress, the major findings of MOSAIC and NSABP C-07 trial in 2004 proved that the addition of oxaliplatin The MOSAIC and NSABP C-07 studies were a milestone in the field of adjuvant therapy for colon cancer, as the combination of oxaliplatin and 5FU analogues remains the standard of care for postoperative adjuvant chemotherapy in stage III colon cancer until today. . Chemotherapy is not needed after surgery for early-stage colon cancer because early-stage colon cancer surgery has achieved radical cure and adjuvant chemotherapy does not give patients a survival benefit. Guidelines and protocols for adjuvant chemotherapy after colon cancer colon cancer surgery: T3NOMO, patients without high-risk factors, given clinical medical observation or consider capecitabine or 5-FU/LV chemotherapy. T3NOMO, patients with high risk factors for systemic recurrence, or T4N0M0, give 5FU/LV +/- oxaliplatin or capecitabine +/- oxaliplatin or clinical trial or observation. High-risk factors for recurrence included pathologic grade 3 to 4, lymphatic/vascular infiltration, intestinal obstruction, <12 lymph nodes sent for examination, peripheral nerve infiltration, local perforation or proximity to the cut edge, and uncertain or positive nature of the cut edge. (The use of nerve invasion as a high-risk factor for recurrence of stage II colon cancer was proposed by Chinese experts). T1 to 3, N1 to 2, M0 or T4,N1 to 2, M0, FOLFOX or CapeOX or capecitabine or 5-FU/LV regimen is preferred for adjuvant chemotherapy. 3. The efficacy of chemotherapy for advanced colorectal cancer is progressing Fluorouracil analogues have been used as an effective chemotherapeutic agent for the treatment of advanced colorectal cancer for more than 40 years. In order to improve the efficacy, investigators have made different attempts in the mode of administration of 5FU, dose intensity and combined biomodulators, with a median survival of 10 to 14 months. The advent of oxaliplatin and irinotecan has ushered in a new era in the treatment of patients with advanced colorectal cancer. Oxaliplatin is a third-generation platinum derivative that induces apoptosis mainly by forming a complex with DNA and blocking DNA double-stranded replication and transcription. Oxaliplatin 130 mg/L once every three weeks has an efficiency of 10-24% for a single drug, and the main toxic side effect is neurotoxicity. Saline configuration is prohibited and cold stimulation is avoided. Irinotecan is a semi-synthetic derivative of camptothecin that causes DNA double-strand breaks and cell death through inhibition of topoisomerase I. The efficiency of single drug is 26-32%, and the main toxic side effects are diarrhea and bone marrow suppression. Capecitabine, an oral fluorouracil analog, can be degraded to 5FU by the higher thymidine phosphorylase in tumor tissues, resulting in significantly higher drug concentrations in tumor sites than in normal tissues. A twice-a-day oral dosing treatment pattern can mimic the steady-state blood concentrations provided by continuously infused 5-FU. The efficiency of capecitabine is higher than 5FU/LV, the safety is better than 5FU/LV, and the incidence of toxic side effects such as diarrhea, gastric mucositis and nausea is significantly lower than 5FU/LV, and the main toxic side effect is hand-foot syndrome. The recommended first-line chemotherapy regimens are FOLFOX, Mfolfx6+bevacizumab, Capeox, Capeox+brivacizumab, FOLFIRI, FOLFIRI+brivacizumab, FOLFIRI+cetuximab, capecitabine, etc. The median survival time of patients with advanced colorectal cancer exceeds 20 months. 4. Pay attention to preoperative and postoperative synchronous radiotherapy for rectal cancer The local regional recurrence rate of resectable stage II to stage III rectal cancer after radical surgery is 15-65%, and even with total rectal mesenteric resection, the local recurrence rate of stage III patients is still as high as 20-30%. To improve the local control rate and long-term survival, this group of patients should undergo standard adjuvant treatment for rectal cancer: preoperative radiotherapy, preoperative simultaneous radiotherapy and postoperative simultaneous radiotherapy. Preoperative concurrent radiotherapy has gradually become the standard treatment for stage II-III surgically resectable rectal cancer. A series of studies suggest that preoperative simultaneous radiotherapy can further reduce the local regional recurrence rate and improve the pathological complete remission rate, and preoperative simultaneous radiotherapy has less toxic side effects and lower local recurrence rate compared with postoperative radiotherapy. For locally advanced inoperable resectable rectal cancer, preoperative simultaneous radiotherapy is the only standard treatment, and most patients can undergo radical resection after radiotherapy. The key is for the first consulting physician to recognize that the principles of treatment for rectal cancer are different from those for colon cancer.