Many people with colon cancer experience no symptoms in the early stages of the disease. However, some symptoms include a persistent change in your bowel habits, including diarrhea or constipation or a change in the consistency of your stool; Rectal bleeding or blood in your stool; Persistent abdominal discomfort, such as cramps, gas or pain; A feeling that your bowel doesn’t empty completely; Weakness or fatigue, or unexplained weight loss.