What does colon cancer make your stool look like?

Grossly normal: Most patients with colon cancer have normal appearing stools. There may be some blood occasionally mixed or covering the stool, but usually this is microscopic rather than obvious. If the cancer is advanced, causing obstruction, then the stools can be narrowed, but again, this is for patients with advanced sigmoid or rectal cancers. The best way to diagnose colon cancer is with a colonoscopy.