Most rectal cancer patients have no obvious pain. If the rectal cancer is in low location it may cause pain in the perineum. Middle or high rectal cancer is affected by autonomic nerves and the pain is very mild. Rectal cancer with low location may be affected by somatic nerves, so it may cause anal pain or perineal pain. If the patient has large rectal cancer or late stage of the disease, the patient will have abdominal pain, mostly in the left lower abdomen, when obstruction symptoms appear, and the pain may be relieved after defecation. If the obstruction is very obvious, it may lead to more accumulation of feces and gas in the sigmoid colon and descending colon, and the patient may have acute intestinal obstruction symptoms, mainly manifested by abdominal distension, accompanied by paroxysmal abdominal pain.