Rectal cancer is a common malignant tumor in the gastrointestinal tract, second only to stomach and esophageal cancer in incidence, is the most common part of colorectal cancer (accounting for about 65%), the majority of genetic patients are over 40 years old, more common in men, the ratio of men to women is 2.3:1, rectal cancer is a lifestyle disease. It has now jumped to the second place in the list of cancers, so diet and lifestyle, is the bane of cancer. Because of the similarity of causes and symptoms, rectal cancer is often mentioned together with colon cancer. Once rectal cancer is diagnosed, under what circumstances will radiation and chemotherapy be used? At present, for rectal cancer, neoadjuvant chemotherapy and radiotherapy are recommended for patients whose tumors invade the muscle layer or have positive lymph nodes before surgery, and the international trend is to advocate radiotherapy and chemotherapy at the same time. For patients who have undergone surgery, if they have positive lymph nodes, adjuvant radiotherapy is recommended after surgery. For patients who do not have positive lymph nodes, but have high-risk factors, such as invasion to the extra-plasma membrane, lymph node dissection not reaching 6, or patients with vascular cancer emboli or younger patients, such patients are also recommended to undergo adjuvant radiotherapy after surgery. What are the side effects of radiotherapy and chemotherapy for rectal cancer? Radiotherapy and chemotherapy have strong side effects on rectal cancer, such as gastrointestinal reactions, inflammation of oral mucosa, painful diarrhea in the gastrointestinal tract, effects on liver function, rising transaminases, and effects on the hematopoietic system, mainly on the blood, including white blood cells, platelets and hemoglobin, which are all effects of chemotherapy. Because radiotherapy is localized, the reaction caused by the whole body is not too big, but the local reaction is heavier. Patients have colon syndrome during radiotherapy, often found to have constipation, the frequency of stool increases, and always have a feeling of constipation, in addition to the discharge of mucus, radiotherapy after a period of time, about a few months to gradually reduce, precise radiotherapy has been able to reduce the side effects to a minimum. We should not be afraid of the side effects of radiotherapy, because the treatment itself is obviously more beneficial than harmful to the patient, and has obvious benefits for the patient, and for these treatments, doctors try to find ways to reduce these side effects, but the patient should actively cooperate with the treatment.