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Colon cancer. Coloured scanning electron micrograph (SEM) of goblet cells (three holes) on the mucosal surface of a cancerous colon. Numerous microvilli (hair-like projections) cover the whole surface. These absorb nutrients and secrete digestive substances. The goblet cells secrete the mucus that lines the intestinal tract. Colon cancer is one of the most common cancers in the developed world. Symptoms include blood in the faeces, constipation or diarrhoea, and abdominal pain. Treatment often involves surgery and chemotherapy. Cancer is the abnormal proliferation of malignant cells. Magnification unknown. (KEYSTONE/SCIENCE PHOTO LIBRARY/STEVE GSCHMEISSNER)