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Colon cancer. Coloured scanning electron micrograph (SEM) of the mucosal surface of a cancerous colon (large intestine). Numerous empty areas are seen that usually contain goblet cells (purple, one at upper left). Goblet cells secrete mucus to lubricate the surface, and their absence may be due to the cancer. Epithelial cells make up the rest of the surface, and are covered in many small (just visible) absorptive microvilli. Colon cancer is one of the most common cancers in the developed world. Symptoms include faecal blood, constipation or diarrhoea, and abdominal pain. Treatment involves surgery and chemotherapy. Magnification unknown. (KEYSTONE/SCIENCE PHOTO LIBRARY/STEVE GSCHMEISSNER)