Black stool is not necessarily caused by cancer or will definitely develop into cancer; there are many reasons for black stool, which may be caused by physiological factors such as intake of dark-colored food or blood products; it may also be caused by benign diseases such as bleeding from gastric ulcers, or malignant diseases such as gastric cancer. 1. Physiological factors When ingesting blood products such as pig’s blood, duck’s blood, etc., or foods such as spinach, black sesame, mulberry, etc., it may lead to dark feces, and this dark feces usually disappears after stopping the intake of such foods. 2. Pathological factors (1) Benign diseases: when the occurrence of gastrointestinal chronic bleeding disease, such as gastritis gastric ulcer, duodenal ulcer and other diseases, will lead to black stools; at the same time will be accompanied by abdominal pain and other symptoms. (2) Malignant diseases: When malignant diseases such as gastric cancer occur, it will lead to black stools, which may be accompanied by symptoms such as progressive weight loss, anemia, and fatigue and depression. When persistent black stool occurs, it is recommended to go to the hospital in time for consultation and standardized treatment under the guidance of professional doctors, so as to avoid delaying the condition.