What are the signs and symptoms of colon polyps?
Ninety-five percent of colon polyps do not cause symptoms or signs, and are discovered during screening or surveillance colonoscopy.
When symptoms or signs occur they may include:
- Red blood mixed in with or on the surface of the stool
- Black stools if the polyp is bleeding substantially and is located in the proximal colon (cecum and ascending colon)
- Iron deficiency anemia if the bleeding has been slow and occurring over a prolonged period of time.
- Weakness, light-headedness, fainting, pale skin, and rapid heart rate due to iron deficiency anemia
- The presence of invisible (occult) blood in stool that is tested when screening for colon cancer at visits to a doctor's office (Because of the tendency of polyps to bleed slowly, intermittently and in small amounts, occult blood testing of stool often is used to screen for colon cancer.)
- Rarely diarrhea when large villous polyps secrete fluid into the intestine
- Rarely constipation if the polyp is very large and obstructs the colon
- Rarely intussusception, a condition in which a polyp drags the portion of the colon to which it is attached into the more distal colon (i.e., telescopes into the more distal colon) and leads to obstruction of the colon. This can cause all of the signs and symptoms of intestinal obstruction including abdominal pain and distention, nausea and vomiting.
How common are colon polyps?
Colon polyps are very common. They increase in prevalence as people age; by age 60, one-third or more of 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, there is a familial, genetic abnormality that causes patients 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.
Why are colon polyps important?
Colon polyps are important because they may give rise to colon cancer. The type of polyp predicts 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 although this is unusual unless the cancer has invaded into the wall of the colon.
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 (spread to other parts of the body). If they are not removed, invasion and metastasis may occur.