In the colon and rectum, tumours can form in the colorectal mucosa. We distinguish between harmful (“malignant”) and non-harmful (“benign”) tumours. A malignant tumour is one that does not respect the boundaries of the organ it occurs in and can therefore grow into other organs. Such tumours can also metastasise (i.e. “spawn” other tumours): intestinal tumours that do so often target the liver and lungs.
Benign intestinal tumours cannot do this and therefore do not pose an immediate threat. In the course of time, however, we know that they may develop into malignant tumours, i.e. we observe a change in their type. Accordingly, adenomas are removed during colonoscopy; the pathologist can then classify them in more detail. This diagnosis then forms the basis for the screening interval.