Colon cancer. Coloured transmission electron micrograph (TEM) of a section through an adenocarcinoma of the colon, part of the large intestine. Malignant columnar epithelium is shown. An adenocarcinoma is a malignant (cancerous) tumour 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 and fat and low in fibre may play a part. Symptoms include a change in bowel habits and blood in the faeces (haematochezia). Treatment may involve partial or complete removal of the colon (colectomy). Human tissue. Magnification: x1000 when printed at 10 centimetres across