Initially benign intestinal tumour. Polyps may occur throughout the large intestine, and sporadically in the small intestine, increasing with the age of the patient. In later life about 10 per cent of the population has one or more polyps, particularly in the last section of the large intestine. They can also be hereditary, so-called polyposis coli, but this is rare. Intestinal polyps usually cause no symptoms, but there can be slight blood loss or even significant haemorrhage with bright blood in the faeces, or black faeces (melaena, when the blood is partly digested). Large polyps can cause sporadic intestinal obstruction. Certain polyps (so-called villous adenoma) are more likely to become malignant (intestinal cancer); in others the likelihood is slight. Most malign intestinal tumours do not originate from polyps. If the above symptoms occur the possibility of a malignant tumour must always be investigated, by contrast X-rays or by rectoscopy. The polyp may possibly be removed at the same time. As a rule any polyp larger than 1 cm, or a rapidly-growing polyp, must be removed and examined in a laboratory (biopsy).