Colon cancer. Gross clinical specimen of a primary malignant (cancerous) tumour (neoplasm, black, centre left) of a human colon. It is at the junction of the large intestine (sigmoid colon) and the rectum, and is known as a colorectal cancer. Colorectal cancers are one of the most common cancers in Western countries. They are thought to be associated with a high-fat, high- meat and low-fibre diet, but genetic factors are also thought to play a part in its development. Symptoms include rectal bleeding and lower abdominal pain. If diagnosed early, surgery can be performed to remove the cancer.