Rectal cancer is one of the common malignant tumors in China, and the most effective treatment method is still surgery, but due to the limitation of pelvic anatomy, it is difficult to remove the peri-cancerous tissues during surgery. Although the rate of anus preservation and long-term survival have improved with the continuous improvement of surgical techniques in recent years, especially after the promotion of total mesorectal excision (TME) technique, the postoperative local recurrence rate is still as high as 8%-40%, and the 5-year survival rate hovers around 50% after surgery. The main reasons for treatment failure of rectal cancer are recurrence and metastasis. Neoadjuvant treatment refers to some treatment methods adopted before surgery, including neoadjuvant radiotherapy and chemotherapy. Neoadjuvant radiotherapy for rectal cancer can not only reduce the clinical stage of tumor and improve the long-term survival rate, but also improve the rate of anus preservation for low and middle rectal cancer. In recent years, neoadjuvant radiotherapy for locally progressive low- and intermediate-stage rectal cancer has been widely appreciated and recognized, and has been written into the 2008 edition of the NCCN guidelines. The significance of neoadjuvant treatment for rectal cancer The effect of neoadjuvant treatment on local recurrence rate and long-term survival rate The killing effect of radiotherapy on tumor includes direct cleavage of DNA strands in the nucleus of tumor cells and indirect killing effect of oxygen free radical generation, among which the killing effect of oxygen free radical depends on the oxygenation of tissues in the irradiated area. After rectal cancer surgery, due to the formation of fibrous scar tissue at the surgical site, the local oxygenation is poor, which directly affects the efficacy of radiotherapy; coupled with the influence of surgery, the patient’s small intestine can be adhered and fixed to the surgical site, and repeated radiotherapy can aggravate radioactive small intestitis and even cause serious complications such as intestinal perforation and intestinal fistula. In contrast, preoperative radiotherapy can completely avoid these situations, improve the efficacy and reduce the incidence of complications. The results of many randomized clinical trials and meta-analyses have shown that preoperative radiotherapy at an effective dose of 30 Gy or more can reduce the relative risk of local recurrence by 50-70%, while postoperative radiotherapy can only achieve a 30-40% reduction. camma et al. conducted a Meta-analysis of 14 RCTs of preoperative radiotherapy for rectal cancer and showed that preoperative radiotherapy reduced the postoperative recurrence rate and 5-year survival rate. A randomized prospective study conducted by Sauer et al. in Germany on 402 cases of stage II and III rectal cancer showed that the postoperative local recurrence rate was 8% in the preoperative radiotherapy group, which was significantly lower than that of 13% in the control group. Kapiteijn reported that there was no difference in the two-year postoperative survival rate between preoperative short-term radiotherapy + TME and TME surgery alone, both of which could reach 82%, but the local recurrence rate in the former was The local recurrence rate was 2.4% in the former and 8.2% in the latter. Neoadjuvant therapy and anal preservation surgery The ability to preserve the anus is one of the goals of successful comprehensive treatment for patients with low- to intermediate-grade rectal cancer. The distance of the tumor from the dentate line, the T-stage of the tumor, and the safe margin of the distal end of the tumor are the key factors to decide whether anal preservation surgery can be performed. For low to medium rectal cancer, preoperative radiotherapy can not only reduce the size of the rectal cancer tumor, but also lower the T-stage of the tumor. This improves the success rate of low anterior resection or colo-anal anastomosis, thus allowing a significant proportion of patients to avoid combined transabdominal perineal rectal cancer resection. In early trials of preoperative radiotherapy, it was found that short-term radiotherapy (one week) reduced postoperative local recurrence rates, but had no significant advantage for surgical anal preservation rates. Later studies found that increasing the intensity of radiotherapy, extending the duration of radiotherapy and the interval between surgeries could achieve tumor downstaging and improve the rate of surgical anal preservation [10]. Modalities of neoadjuvant therapy There is no uniform protocol for neoadjuvant chemotherapy, but it includes 5-Fu/LV or Xeloda (Xeloda), Oxaliplatin (platinum oxalate), CPT-11 (Kepto) and other drugs with high efficacy in colorectal cancer, protocols such as Mayo Clinic, FOLFOX4, FOLFIRI, etc. The duration of chemotherapy is parallel to radiotherapy and can continue until surgery. However, the synergistic mechanism of action between radiotherapy and chemotherapy, and whether the administration of the drug before radiotherapy can increase the sensitivity of the tumor are yet to be confirmed by further clinical trials. Regarding the intensity of preoperative radiotherapy, most of them advocate the use of medium-dose radiotherapy, with the total amount of 40-60 Gy and the fractionated dose of 1.8-2 Gy. Regarding the interval between the end of radiotherapy and surgery, most of them advocate about 6 weeks, during which the tumor tissue is obviously necrotic and fibrotic, which can best reflect the efficacy of radiotherapy. If the interval is too short, it is difficult to achieve the purpose of tumor shrinkage and stage reduction, and it is also difficult to operate because of pelvic congestion and edema; if the interval is too long, tumor regeneration may occur and delay the operation. At present, it is believed that malignant tumor is a systemic disease, and radiotherapy as a local treatment is only to remove the microscopic cancer foci in the intestinal canal and mesentery around the tumor, while adjuvant chemotherapy as a systemic treatment is necessary to prevent and treat the distant metastases of tumor. Given that the purpose of neoadjuvant therapy is to shrink the tumor and reduce the stage, improve the success rate of anal preservation surgery, reduce the local recurrence rate and improve the long-term survival rate, the following cases are not suitable for neoadjuvant therapy: 1. high rectal cancer more than 10 cm from the anal verge; 2. stage T1 tumor without lymphatic metastasis and deep infiltration; 3. proven distant organ metastasis or extensive peritoneal metastasis. or extensive peritoneal metastasis. Rectal cancer is an adenocarcinoma of the gastrointestinal tract, which is not very sensitive to radiotherapy and chemotherapy, such as lower than squamous carcinoma, breast cancer, lymphoma, etc. For patients who are not sensitive to radiotherapy and chemotherapy, preoperative neoadjuvant therapy may not benefit them but may delay their disease. Currently, neoadjuvant therapy is somewhat blinded, and there is no practical way to determine which patients are more sensitive to radiotherapy or a particular chemotherapy regimen. In addition, the question of whether neoadjuvant therapy is overtreatment for patients with early-stage rectal cancer is still inconclusive. Most of the clinical trials that have been completed or are still in progress now target patients in clinical stage T3 and T4. The means of screening and efficacy judgment are based on clinical methods, such as patients’ clinical symptoms, rectal finger examination, endoluminal ultrasound, rectal MRI, etc. Some biological indicators have not been formally used in clinical practice. For patients with complete pathological remission after neoadjuvant therapy, it is still controversial whether surgery is still needed. We believe that complete clinical remission after neoadjuvant therapy is not equal to complete pathological remission, and remission of the primary lesion does not indicate the absence of metastasis of station II and III lymph nodes, so surgical clearance of regional lymph nodes is still quite necessary, and only after completion of local lesion resection and regional lymph node clearance can we have a comprehensive understanding and judgment of the disease staging and postoperative adjuvant therapy .