Dark stool is not necessarily cancer, and cancer does not always have the symptom of dark stool. There can be several cases as follows: 1. If a malignant tumor of the intestinal tract is accompanied by bleeding and the amount of bleeding is relatively small, it will cause dark stools. 2. If there are benign changes in the upper gastrointestinal tract, such as erosive ulcers, some polyps, esophagogastric fundic varices caused by cirrhosis, etc., which cause bleeding in the gastrointestinal tract, it will also cause dark stools. 3. After eating foods that cause dark stools, it will also cause dark stools, such as various blood products, such as duck blood, pig blood, sheep blood, etc. 4. 4, after eating certain drugs can also make the stool black, such as in the treatment of anemia supplementation of various iron, etc..