If there are symptoms, the following may indicate colon cancer: 1  Abdominal pain and tenderness in the lower abdomen. 2  Blood in the stool. 3  Diarrhea, constipation, or other change in bowel habits. 4  Narrow stools. 5  Weight loss with no known reason.
Diarrhea may be caused by: lactose intolerance. bacterial infection. damage to intestinal wall. hormone-producing tumors (including certain types of pancreatic neuroendocrine tumors) inflammation or ulceration of the bowel. malabsorption caused by surgery that has shortened the intestines. pancreatic enzyme insufficiency.
Parasites such as Giardia lamblia and cryptosporidium can cause diarrhea. Common bacterial causes of diarrhea include campylobacter, salmonella, shigella and Escherichia coli. Diarrhea caused by bacteria and parasites can be common when traveling in developing countries and is often called traveler's diarrhea.