Colon Polyps (cont.)

Colon polyps are very common. They increase in prevalence as people age; by age 60, one-third or more people will have at least one polyp. If a person has a colon polyp, he or she is more likely to have additional polyps elsewhere in the colon and is more likely to form new polyps at a later time. In a small subset of patients with colon polyps (less than 5%), there is a familial, genetic abnormality that causes them and other members of their families to develop larger numbers of polyps, to develop them at an early age, and to more frequently have them become cancerous (malignant).

Colon polyps are important because they may give rise to colon cancer. Depending on the type of polyp, they predict who is more likely to develop further polyps and colon cancer. Polyps cause other problems (to be discussed), but it is the deadly nature of colon cancer that is of most concern.

Benign polyps become malignant polyps (cancer) with further mutations and changes in the cells' genetic material (genes). The cells begin to divide and reproduce uncontrollably, sometimes giving rise to a larger polyp. Initially, the increasingly, genetically abnormal cells are limited to the layer of cells that line the inside of the colon. The cells then then develop the ability to invade deeper into the wall of the colon. Individual cells also develop the ability to break off from the polyp and spread into lymph channels through the wall of the colon to the local lymph nodes and then throughout the body, a process referred to as metastasis.

The transition from benign to malignant polyp can be seen under the microscope. In the earlier phase of the transition, called low-grade dysplasia (dysplasia=abnormal formation), the cells and their relationships to one another become abnormal. When the cells and their relationships become even more abnormal, it is termed high-grade dysplasia. High-grade dysplasia is of greater concern because the cells are clearly cancerous although they are limited to the innermost lining of the colon; with rare exceptions, they have not yet developed the abilities to invade and metastasize. If they are not removed, invasion and metastasis may occur.

Source: MedicineNet.com
http://www.medicinenet.com/colon_polyps/article.htm