Does blood in stool always mean cancer?

Not necessarily: Blood in the stool can occur for a variety of reasons, the most concerning of which is cancer. Certainly if there is blood in the stool it needs to be evaluated. The amount of blood, the color of the blood give indications of possible causes. For example, hemorhhoids may bleed from irritation, but may lead to bright red blood in the stool. Cancers may lead to occult blood in the stool.

Not always: Hemorrhoids, non-cancerous polyps, some colon infections, and arteriovenous malformations are just some non -cancerous causes of hematochezia (red bleeding). Ulcers and gastritis are causes of upper GI bleeding that is frequently melena ( black tarry stools). Crohn's disease can cause melena or hematochezia.