What Are the Types of Colon Polyps?

Different types of colon polyps have various shapes or growth patterns. Tubular polyps, for example, have a growth pattern that resembles regularly spaced tubes. Villous polyps have a leaf-like growth pattern, and tubulovillous polyps show a combination of both growth patterns.

Identifying the type of polyp you have can help your healthcare provider understand your risk for colon cancer and develop a treatment and prevention plan to help lower your risk.

This article looks at the different types of colon polyps, including their relationship to cancers of the colon or rectum. It also describes the symptoms and causes of colon polyps as well as the current colon cancer screening recommendations in the United States.

What Are Colonic Polyps?

A colon polyp is a growth on the lining of the wall of your colon (large intestine) or rectum. Polyps are common in people over 50 and tend to grow slowly. Over time, some polyps can develop into colon cancer, which is why they are typically removed during a routine colonoscopy. Tubular adenomas are the most common type, followed by benign hyperplastic polyps.

In most cases, colon polyps do not cause any symptoms. Because of this, polyps can go undetected until they are found during a routine colonoscopy.

When polyps do cause symptoms, they may include:

• Blood in the stool
• Black or tarry stools
• Bleeding from the rectum
• Chronic constipation
• Intermittent bouts of constipation and diarrhea
• Unexplained weight loss
• Severe abdominal pain (often related to bowel obstruction)

Polyps found and removed during a colonoscopy may grow back. This is why it is important to continue to have routine screening as advised by your healthcare provider.

Types of Colon Polyps

There are different types of colon polyps, each of which has its own characteristics and structure. These and other factors (including the size and location of a polyp) can help determine the potential risk of cancer.

There are five broad categories of colon polyps as well as "mixed" types that have characteristics of two or more polyp types.

Tubular Adenomas

Tubular adenomas make up around two-thirds of all colon polyps. They are one of two types of adenomatous polyps that can develop in the colon's inner lining.

Adenomatous polyps, also known as adenomas, originate in epithelial tissues (the thin layer covering organs, cavities, and vessels of the body). Tubular adenomas as so-named because they tend to form in an orderly tubular shape.

Tubular adenomas are considered low risk for developing into cancer.

Villous Adenomas

Villous adenomas are another type of adenomatous polyp that has a greater potential of becoming cancerous. While less common than tubular adenomas, around 30% of villous adenomas will turn into colon or rectal cancer.

The term villous describes the finger-like projection (villi) on the surface of the epithelial tissues. Unlike tubular adenomas that develop in an orderly fashion, villous adenomas develop haphazardly and often have a cauliflower-like appearance.

Tubulovillous Adenomas

Some adenomas share characteristics of both tubular and villous adenomas, called tubulovillous adenomas. These have a greater potential for turning cancerous than tubular adenomas but less than villous adenomas.

Hyperplastic Polyps

Hyperplastic polyps are a type of polyp that rarely ever turns cancerous. The term hyperplasia simply describes an abnormal increase in the number of cells that causes tissues to enlarge. (Benign prostatic hyperplasia, for example, is the term used to describe an enlarged prostate.)

Hyperplastic adenomas tend to develop in parts of the digestive tract where tissues have been previously damaged. Hyperplastic polyps are usually small and situated in the lower end of the colon, such as the rectum and sigmoid colon.

Hyperplastic polyps are considered to be non-neoplastic.

Inflammatory Polyps

Inflammatory polyps are those that arise in tissues damaged by chronic intestinal inflammation. They are mostly found in people with inflammatory bowel disease (IBD), such as Crohn’s disease or ulcerative colitis.

As with hyperplastic polyps, inflammatory polyps are non-neoplastic and, as such, have a very low potential for turning cancerous.

Hamartomatous Polyps

Hamartomatous polyps are a rare type of colon polyp typically seen in children. They may manifest with a single polyp or multiple polyps.

Hamartomatous polyps are considered an inherited genetic condition. While the polyps are non-neoplastic, they are still linked to an increased risk of colon cancer, albeit in different ways.

It is thought that cancer may not arise from the polyps themselves but rather from inherited genetic errors that cause stem cells to divide abnormally. (Stem cells are unspecialized cells that can transform into specialized cells based on signaling molecules, called growth factors, that "tell" the cell what to become.)

This is evidenced by the fact that cancer rarely occurs if there is only one hamartomatous polyp. The differs from adenomas, in which cancer can develop from a single polyp. This suggests that multiple factors, including genetics, contribute to the onset of cancer from hamartomatous polyps.

Shapes and Characteristics of Colon Polyps

When describing a polyp, a diagnostic specialist known as a pathologist will use different terms to describe the characteristics of the growth. Some of these characteristics are linked to an increased risk of colon cancer.

Colon polyps can be described in the following ways:

• Pedunculated: This is a raised, mushroom-like growth that is attached to the lining of the colon by a long, thin stalk (peduncle). Because they are raised, pedunculated polyps are easier to spot and remove, and less likely to turn cancerous.
• Sessile: This is a flat or dome-shaped growth that sits on the colon's lining. Sessile polyps are more likely to become cancerous, in part because they are flat and more easily missed.
• Serrated: This is when the tissues of a polyp have a saw-toothed appearance under the microscope. Having a serrated adenoma significantly increases the risk of colon cancer.

Causes and Risk Factors

Scientists are not exactly sure why some people get colon polyps, and others do not. There is evidence that genetics play a part. This includes having so-called APC, TP53, and KRAS gene mutations, which often run in families.

Certain people are at greater risk of polyps due to non-modifiable (unchangeable) risk factors, such as:

• Being over 50
• Being Black or of Eastern European Jewish descent
• A family or personal history of colon polyps
• A family history of colon cancer
• A personal history of uterine or ovarian cancer

There are also modifiable (changeable) risk factors that may contribute to the onset of colon polyps, including:

• Obesity
• Eating a high-fat diet
• Smoking
• Excessive alcohol use
• A sedentary lifestyle
  

Diagnosis

Colon polyps are usually found during a routine colonoscopy. Other tests can suggest the presence of polyps. For example, a fecal immunochemical test (FIT) or a fecal occult blood test (FOBT) can look for small amounts of blood in your stool. A positive result could mean you have polyps that will need to be removed during a colonoscopy. 

How Are Colon Polyps Treated?

Colonic polyps are typically removed during a colonoscopy. This is done with biopsy forceps or a wire loop that uses an electric current to burn through the tissue. The polyp is usually collected and then sent to a laboratory so it can be tested for cancer.

If you have polyps removed, you will need to repeat your colonoscopy sooner than what would be recommended if you did not have polyps. How soon depends on the polyps' size, number, and type.

How Are Colon Polyps Prevented?

Certain risk factors such as your age and family history of colon polyps can't be changed. However, there may be ways to reduce your chances of developing polyps. The most important of these is your diet. Eating more fruits and vegetables and decreasing your intake of red meat may help reduce your risk of developing polyps.

Other lifestyle choices may also play a role in the development of colon polyps, including:

• Getting the recommended amount of physical exercise
• Losing weight
• Quitting smoking and reducing or avoiding alcohol use

Calcium, folic acid supplements, and a daily low dose of aspirin may also protect against the development of polyps in some people.

Colon Cancer Screening

The best way to avoid colon cancer is to undergo routine colorectal cancer screening, Updated guidelines from the American Cancer Society and U.S. Preventive Service Task Force recommend screening starting at age 45 for adults at average risk of the disease.

The screening should be repeated every one to 10 years based on the type of test used:

• Colonoscopy: Every 10 years
• Flexible sigmoidoscopy: Every five years
• Virtual colonoscopy: Every five years
• Stool-based tests: Every one to three years, depending on the test

Those at high risk because of a family history of colon cancer or other factors can be screened at an earlier age and tested more frequently.

Summary

Colon polyps are abnormal tissue growths in the colon's lining (large intestine). Many polyps are harmless, but some have the potential to turn cancerous.

Tubular and villous adenomas are two polyps that can sometimes develop into colon cancer, while inflammatory and hyperplastic polyps rarely do. Hamartomotous polyps found in children can also lead to cancer, albeit by different means.

To prevent polyps from turning cancerous, routine colon cancer screening is recommended. This includes direct and indirect screening methods such as colonoscopy, sigmoidoscopy, virtual colonoscopy, or stool-based tests.