Light micrograph of a section through an adenocarcinoma of the colon, part of the large intestine. An adenocarcinoma is a malignant (cancerous) tumor of the lining (epithelium) of glandular structures. Cancer of the colon has no single cause but genetic factors and a diet that is high in meat & fat and low in fiber may play a part. Symptoms include a change in the bowel habits and blood in the feces (hematochezia). Treatment may involve partial or complete removal of the colon