Blood in stool is one of the early symptoms of all colorectal cancers, but the timing and nature of bleeding varies in different parts of the tumor. For rectal cancer, the early amount is very small, mostly with fresh blood traces on the side of the stool. A few patients can discharge a large amount of fresh blood after stool. In contrast, the bleeding from tumors in all segments of the colon may darken due to longer stay in the intestinal tract, and the color of the blood in stool may become darker to discharge violet or black-purple stool. Often, the blood is not detectable to the naked eye due to the small amount of blood or the long retention time, and only a positive stool occult blood test is available. Changes in stool habits include changes in the timing and frequency of stools, and alternating constipation and diarrhea. Sometimes the stool is just mucus and blood, and there is a feeling of incomplete defecation. Painful defecation About 50% of rectal cancer patients have pain during defecation, the degree of which may be mild or severe. Abdominal pain Some patients have vague abdominal pain as the prominent symptom, while others show paroxysmal colic with abdominal distension. Weakness, anemia and abdominal mass In the right hemicolectomy, due to the way the mass grows and failure to detect it in time, the mass can often be palpated in the abdominal wall and systemic manifestations such as anemia have already appeared.