(1) Blood in the stool: in mild cases, only positive fecal occult blood test; in severe cases, mucus-blood stool, mucus-pus-blood stool or pure blood stool. When mucus blood stool or mucus pus blood stool is shown, it is often misdiagnosed as dysentery and the diagnosis is delayed. (2) Abdominal pain: When colorectal cancer has erosion and secondary infection, abdominal pain may appear due to increased peristalsis and spasm of the corresponding intestinal segment. Some patients have persistent vague abdominal pain as the first or prominent symptom. When the pain is present in the right lower abdomen, it is often misdiagnosed as chronic appendicitis. Other patients present with typical abdominal pain of incomplete intestinal obstruction. (3) Change in bowel habits with constipation, diarrhea, or alternating between the two: Most people have a good habit of having a regular bowel movement once a day. If there is no other reason (including travel, change of living environment and taking hyoscine, etc.) and constipation and diarrhea occur frequently, it should be noticed. Patients have several or even more than ten bowel movements per day, which can be mucus and blood, mucus and pus and blood, or even loose stools to the eye. (5) Anemia: male patients, especially those without other causes of blood loss or intestinal parasitosis, should think of the possibility of gastric or colorectal cancer if progressive iron deficiency anemia is found.