Colon cancer. Light micrograph of a section through a mucinous adenocarcinoma (purple lobes) of the large intestine or colon. Healthy colon tissue (pink) is seen at bottom and right. An adenocarcinoma is a malignant (cancerous) tumour of the lining (epithelium) of glandular structures. This tumour is termed mucinous because it largely consists of mucous secretion (white spaces). Cancer of the colon has no single cause but genetic factors and diet are thought to affect the risk of developing it. Symptoms include blood in the faeces. Treatment may involve partial or complete removal of the colon (colectomy). Magnification unknown.