If the surface of bowel cancer has broken down and bleeding, the patient will have blood in stool when defecating. If the bleeding on the surface of bowel cancer has stopped, the patient will not have blood in stool, but may have formed stool or yellow stool, which is mainly determined by the size of the tumor and the nutritional status of the patient. If the tumor is very large, with many surface ulcers and erosions, the patient may have blood in stool every time, which means that the bleeding on the surface of the tumor is difficult to stop by itself. However, the surface may break down and bleed again, so the patient may have blood in the stool again after a period of time.