Rectal cancer refers to cancer between the junction of sigmoid colon and rectum to the dentate line, and is one of the most common malignant tumors of the gastrointestinal tract. At present, the clinical classification of rectal cancer is divided into ulcerative type, mass type and infiltrative type. The histological typing is divided into adenocarcinoma (tubular, papillary, mucinous and indolent cell carcinoma) adenosquamous carcinoma and undifferentiated carcinoma. Lymphatic metastasis is the main route of metastasis and spread, but it can also infiltrate directly into the surrounding tissues and metastasize through blood flow. Clinical manifestations 1. Blood in stool: It is one of the common symptoms of rectal cancer. About 80% of patients have blood in stool at the beginning of the disease, and the bleeding is small at the beginning, which is seen on the surface of stool, and often accompanied by pus and blood after combined infection. 2. Rectal irritation symptom: it is manifested as frequent bowel movement, change of defecation habit, discomfort of anal drop before defecation, feeling of urgency and heaviness and incomplete defecation, and in advanced stage, it invades the pre-sacral nerve and is often accompanied by severe pain. 3.Symptoms of intestinal obstruction: The cancer invades the intestinal canal and causes narrowing of the intestinal cavity, which initially leads to deformation and thinning of stool. 4.Concomitant symptoms: late stage cancer invading prostate and bladder may cause urinary frequency, urinary urgency, urinary pain and hematuria. When liver metastasis occurs in late stage, there may be ascites, hepatomegaly, jaundice, anemia, emaciation, weakness, cachexia, etc.