A polyp is a growth that occurs on the lining of your large intestine that, left unchecked, can become cancer, especially if colon cancer runs in your family.
What is a polyp?
Colon polyps are tissue growths on the wall of your large intestine that are very common.
They’re important because some types of polyps could become malignant. Polyps also are important because, based on their size, number, and anatomy, they can be an indicator of future potential for colon cancer, especially if it runs in your family.
They affect about 20 to 30 percent of American adults. Polyps can grow flat against the lining of the colon or on stalks like mushrooms. They can grow on any part of the colon, but most often occur on the left side.
In one study of cancerous polyps in patients, more than 900 polyps were found in just over 700 patients. Just over 50 of the polyps were cancerous.
The majority of polyps do not become malignant, but having them removed may reduce your future risk for colorectal cancer.
Polyps are typically detected during a colonoscopy, in which a long, thin, flexible tube with a camera attached is used to examine the colon walls. The doctor leading the colonoscopy will remove any polyps during the colonoscopy, with an attachment to the tube. The tissue can later be examined in the lab to search for signs of malignancy.
At least 30 percent of patients will develop new polyps, which is why follow-up colonoscopies are so important. This is usually done 3 to 5 years after polyp removal.
Some people develop just one polyp, but it’s common to develop two or more. It’s uncommon to have more than five.
Types of polyps
There are many types of polyps, some having the potential to become cancer, while others don’t. Two of the most common types of polyps are hyperplastic and adenomatous.
Hyperplastic polyps are small and are generally seen as harmless and probably won’t develop into cancer.
Adenomas also are common and small, but can be bigger. There is a greater chance that bigger adenomas may develop into cancer over time. Most colorectal cancers develop from a polyp that has been present for 5 to 15 years.
The exact risk of an adenoma turning into cancer is difficult to predict, although studies have set the risk as about 1 in 12 after 10 years, and 1 in 4 after about 20 years. Risk seems to vary based on the size of the adenoma and its exact subtype, some of which are more prone to develop into cancer than others.
Polyps can also occur because of polyposis syndromes, a group of hereditary conditions. They are rare and usually occur in young people. They often cause multiple colonic polyps that have a high chance of turning into cancer.
Symptoms of colon polyps
Polyps usually do not cause symptoms. Some people, however, may experience rectal bleeding, which can also be a sign of hemorrhoids or a tear in your anus. Other symptoms include:
- Change in stool color
- Change in bowel habits
- Pain, nausea, or vomiting
- Iron deficiency anemia (do to bleeding from your polyps)
What causes polyps?
Colonic polyps are caused by an abnormal production of cells. The lining of the bowel constantly renews itself, and chronic inflammation or a faulty gene can cause the cells in the bowel lining to grow more quickly.
Scientists at John Hopkins University were the first to describe how a polyp progresses to colorectal cancer. They discovered that polyps and colorectal cancer develop as a result of genetic mutations or other chemical changes, causing inactivation or promotion of genes known as tumor suppressors or tumor promoters.
The adenoma is considered the precursor to colorectal cancer and rarely occurs in people under age 49, which is why people are urged to start having colonoscopies by age 50.
For people age 50 and older who do not have any risk factors for colon cancer other than age, colonoscopies are typically recommended once every 10 years, beginning at age 50. People who have additional risk factors may need colonoscopy more often than that and start having them at a younger age. If you've had one or more polyps removed, you are more likely to get additional polyps in the future.
Prevention of colon polyps is a matter of eating more fruits and vegetables, and losing weight if you’re overweight. Some research suggests that getting more calcium and vitamin D may lower your risk of developing polyps.
Research also suggests that avoiding fatty food, red meat, and processed meat such as hot dogs and lunchmeats can help you prevent colon polyps. Polyps are more common in industrial countries, suggesting that lifestyle and environment may be a contributor. Risk factors include high-fat diet, high red meat diet, low fiber, cigarette smoking, and obesity.
March 18, 2020
Christopher Nystuen, MD, MBA