Some of the symptoms of colorectal cancer include: A change in bowel habits that lasts more than a few days, such as diarrhea, constipation or narrowing of the stool Bright red or very dark stool coloration, which could indicate the presence of blood A feeling that the bowel does not empty completely Frequent gas pains, bloating, fullness or cramps Unintended weight loss Exhaustion Vomiting Moffit