Colon cancer can cause changes in stool, including blood, looser consistency, or increased frequency. Symptoms like abdominal pain, narrow “pencil” stools, and rectal bleeding may occur, though not all patients show signs, and stools can appear normal.

Early indicators include “narrow stools” due to tumor growth, pain during defecation, or a feeling of incomplete bowel emptying (tenesmus). Rectal bleeding and fatigue from anemia are also common early signs.

As cancer progresses to stage three, symptoms worsen. These include constipation, diarrhea, alternating bowel habits, blood in stool (bright red or dark, depending on tumor location), and abdominal bloating. Persistent inflammation may lead to more severe tenesmus.

Colon cancer progression often causes bowel obstruction and iron deficiency anemia, with bleeding that may not always be visible in stool. Any unexplained, persistent stool changes should prompt medical attention.