According to anatomy, human colon can be divided into right half colon and left half colon, and left colon cancer occurs in left half colon, and the clinical manifestations of left half colon cancer are as follows: 1) abdominal pain, which is usually manifested as pain in the left side of the abdomen; 2) poor appetite, patients don’t like to eat, fatigue, and lethargy, etc; 3) change of bowel habit, and the patients may change from the usual regular bowel movement to increased number of bowel movements or constipation; 4) change of bowel color and character, and some patients may have the manifestations of having blood in the stools and black color in the stools, etc.; 5) the patients with left half colon cancer may even have the manifestations of intestinal obstruction due to the growth of tumors, such as abdominal pain, abdominal distension, nausea, and vomiting.