So whether the blood in the stool is light or dark says nothing about the malignancy of the disease?
Not necessarily. Bright-coloured blood can indicate polyps, for example, which are benign growths inside the colon that begin to bleed when they reach a certain size. These are mostly painless. The polyps should be surgically removed so that they don’t develop into colon cancer. Light-coloured blood can also be an indication of tumours in the stomach or small intestine, although these are not necessarily malignant.
Dark blood in the stools
Black blood may be a bacterial infection in the stomach or duodenum, which can usually be treated with medication. Sometimes, however, chronic inflammatory bowel diseases such as ulcerative colitis or Crohn's disease are the cause. In this case, a gastroscopy or a colonoscopy, i.e. tissue samples, will provide clarification.