Colorectal cancer is formed by the malignant transformation of cells in the colon and rectum tissues. Risk factors for the onset of the disease: age older than 50, family history of colorectal cancer, history of colorectal cancer, ovarian cancer, endometrial cancer or breast cancer, history of colorectal polyps, history of inflammatory bowel disease, etc. Main symptoms: change of stool regularity, blood in stool (fresh blood stool or black stool), diarrhea, constipation or frequent feeling of incomplete stool, thinning of stool, repeated abdominal distension or cramping pain, unexplained wasting, extreme sleepiness, vomiting. Examination and diagnostic methods: physical examination and medical history, fecal occult blood test, rectal examination, barium enema, colonoscopy and biopsy, simulated colonoscopy. Factors affecting prognosis: tumor stage, whether there is intestinal obstruction or intestinal perforation, tumor recurrence or not, patient’s physical condition. The basis of treatment selection: tumor stage, whether the tumor has recurred, patient’s physical condition. Surgical treatment Surgical removal of tumor is the most common treatment method for colorectal cancer, including: local excision, radical resection (including lymph node removal in the drainage area), radical resection and colostomy, radiofrequency ablation, cryosurgery. Even if the surgeon is able to remove the entire naked eye tumor during surgery, some patients still need to receive chemotherapy or radiation therapy after surgery to kill any cancer cells that may remain. Chemotherapy (chemotherapy) and biologic therapy Commonly used drugs include 5-fluorouracil (5-FU), capecitabine (Xyroda), oxaliplatin, irinotecan (CPT-11), cetuximab (Eptifibat), etc. Calcium folinic acid (LV) enhances the efficacy of 5-FU. 5-FU is best administered by continuous intravenous drip, especially when combined with oxaliplatin or irinotecan. Capecitabine is also ineffective after failure of a 5-FU-containing chemotherapy regimen. Capecitabine dosage should be adjusted as appropriate when creatinine clearance is reduced. Irinotecan is not currently used for postoperative adjuvant chemotherapy. Adjuvant therapy: chemotherapy, radiotherapy and biotherapy after surgery are called adjuvant therapy to improve the cure rate. Indications for adjuvant chemotherapy: Stage II and III patients; Stage I with unfavorable factors (e.g., positive cut margins, vascular invasion, poor differentiation, too few lymph nodes sent for examination). Adjuvant chemotherapy regimens: 5-FU/LV, 5-FU, capecitabine (Hirudar), FLOX, FOLFOX4, mFOLFOX6. Chemotherapy for inoperable or metastatic colon cancer: first-line chemotherapy (FOLFOX, CapeOX, FOLFIRI, 5-FU/LV, capecitabine) + bevacizumab (currently not available in China); second- and third-line regimens mostly is to replace the chemotherapy regimen, which can be added to chemotherapy with cetuximab (Ebiximab). Liver metastases are treated with chemotherapy → resection of metastases; radiofrequency ablation or cryosurgery; hepatic artery embolization chemotherapy combined with radiotherapy. Those who had chemotherapy before surgery can switch chemotherapy. (Note: FOLFOX: 5-FU/LV/oxaliplatin, FOLFIRI: 5-FU/LV/CPT-11, CapeOX: oxaliplatin + Siroda) Radiation therapy (radiotherapy) Since the rectum does not have a plasma membrane layer and is closely connected to the surrounding tissues, thus making the tumor easily invasive, coupled with the fixed anatomical position of the rectum, radiotherapy is widely used in the preoperative and postoperative treatment of rectal cancer. Therefore, radiotherapy is widely used in the preoperative and postoperative treatment of rectal cancer. From stage I to stage IV or recurrent rectal cancer, radiotherapy plays an important role. In the palliative treatment of advanced colon cancer, radiotherapy can relieve the symptoms of bowel obstruction and bleeding caused by the tumor. Follow-up Follow-up is to check patients’ health status, test blood CEA level and imaging examination regularly after the end of treatment, so as to evaluate the efficacy, guide the follow-up treatment and monitor whether the tumor recurs.