What is a most common manifestation of colon cancer?

No symptom: Get a colonoscopy if age over 50, sooner if family history of colon cancer or having symptoms ( blood in stool, prologued diarrhea, unexplained abd pain, weight loss, bowel obstruction).

Rectal bleeding: Rectal bleeding and or abdominal pain are common symtoms but most early colon cancers are asymptomatic. So the best way to check for colon cancer is to do screening tests to check the inside of the colon by means of colonoscopy or a barium enema study.