Adenomatous Polyp in the Colon: Meaning and Cancer Risk

Removal of polyps during colon cancer screening may prevent cancer

An adenomatous polyp, also known as an adenoma, is an abnormal growth that forms on the colon's lining (large intestine). An adenomatous polyp resembles the colon's normal lining but differs in several key ways when examined under the microscope.

Adenomatous polyps are common, comprising around 70% of all colon polyps. Roughly one-third to one-half of all people will develop one or more adenomatous polyps in their lifetime.

Most adenomatous polyps are benign (noncancerous) and do not cause any symptoms. With that said, different types of adenomas vary by location and structure, some of which are more likely to turn malignant (cancerous) than others.

This article describes the causes and symptoms of adenomatous polyps as well as how these polyps are diagnosed and treated. It also walks you through what a pathology report means if a polyp is found during a routine colonoscopy.

Verywell / Julie Bang

Adenomatous Polyp Symptoms

Adenomatous polyps do not cause symptoms unless they progress to colon cancer. Even then, there may be no sign of a problem until the malignancy is advanced. This is why colon cancer screenings are so important.

Among the possible symptoms of an adenomatous polyp are:

  • Abdominal pain: Most polyps will not cause any pain until they grow large enough to cause a blockage in the colon. 
  • Anemia: A bleeding polyp, even if it is only causing a small amount of blood loss that isn’t visible in stool, can lead to anemia. 
  • A change in stool color: Blood in the stool can make it appear red, maroon, dark, or black, depending on where the bleeding occurs.
  • Changes in bowel habits: A large polyp can obstruct the colon and lead to constipation. At the same time, the blockage can cause fluids to build up behind the obstruction and trigger bouts of diarrhea
  • Rectal bleeding: Visible bleeding can be caused by many different things, such as hemorrhoids, but should be looked at if it lasts for more than a day or two, or earlier if it worries you.

What Causes Adenomatous Polyps?

Adenomatous polyps can form anywhere in the large intestine. There is no known way to prevent polyps from growing altogether, although some known risk factors are modifiable and can be avoided.

Gene mutations can contribute to the formation of adenomatous polyps because they cause cells to divide in an unregulated way. Some of these mutations (such as APC, TP53, and KRAS) are associated with an increased risk of colon cancer.

While there’s no way to pin down the specific cause of polyp formation, there are a few things that can increase your risk of developing polyps and colorectal cancer:

  • Age: Polyps are more common in people over 50.
  • Race and ethnicity: Black people and people of Jewish Eastern European descent are at an increased risk of colon cancer.
  • Family history: Having a first-degree family member with colon polyps (such as a parent or sibling) increases your risk of colon polyps by roughly 50%.
  • Smoking: Smoking cigarettes doubles the risk of developing adenomatous polyps.
  • Inflammatory bowel diseases: Adenomatous polyps are more common in people with inflammatory bowel diseases like Crohn’s disease and ulcerative colitis
  • High alcohol consumption: Drinking 25 grams (one fluid ounce) of alcohol daily increases the risk of adenomatous polyps.
  • Type 2 diabetes: The risk of adenomatous polyps is greater in people with poorly controlled type 2 diabetes than those who can manage their blood sugar.

Diagnosis

Because most colon adenomas are asymptomatic (occurring without symptoms), they are typically diagnosed during a colonoscopy by a specialist known as a gastroenterologist.

If a polyp is found, it may or may not be removed using a procedure known as a polypectomy. The decision to remove or not remove a polyp is based on the size of the growth as well as its location and appearance.

Areas of concern within the colon will be marked with a tattoo and noted in the pathology report. In this way, the gastroenterologist can return to the area during the next scheduled colonoscopy to check for any changes.

Fewer than 5% of adenomatous polyps progress to cancer over the course of seven to 10 years.


Updated Colon Cancer Screening Recommendations

Adenomatous polyps are found during various colorectal cancer screening tests. It is important for people to receive screening for colorectal cancer at regular intervals based on recommendations from a physician.

Screening recommendations from the American Cancer Society (ACS) and U.S. Preventive Services Task Force (USPSTF) were updated in 2021. Both now recommend colon cancer screening starting at age 45 or younger for those at an increased risk.

Depending on the type of test used, screening may be recommended every one, three, five, or 10 years.

Colonoscopy

During a colonoscopy, a long tube with a light and a camera on the end is used to look inside the colon and find abnormalities such as adenomatous polyps. People prepare for a colonoscopy by using strong laxatives to remove all stools from the colon. Monitored sedation commonly puts a person in "twilight sleep."

The benefit of this test is that when a polyp is found, it can be removed and the tissue sent for testing. Biopsies are also taken during a colonoscopy, which can be analyzed to see if there are any concerning characteristics of the cells in the colon.

Colonoscopy should be repeated every 10 years.

Flexible Sigmoidoscopy

A flexible sigmoidoscopy is done by inserting a tube with a light and a camera on the end into the rectum and looking at the last section of the colon, which is the sigmoid colon. This test may be done with or without prep and with or without sedation.

The limitation of this test is that only the sigmoid section can be seen, which means the physician will not visualize the rest of the colon. Adenomatous polyps further up in the colon can not be seen or removed.

Flexible sigmoidoscopy should be repeated every five years.

Virtual Colonoscopy

A virtual colonoscopy, also called a CT colonography, is done by using imaging to look at the colon. This test is less invasive than a conventional colonoscopy but a colon prep to clean the bowel of stool is necessary.

A thin tube is inserted approximately two inches into the rectum, and a CT scanner (a large imaging machine shaped like a donut) takes a series of images.

Virtual colonoscopy should be repeated every five years.

Stool-Based Tests

A stool test will be used to look for signs of polyps and/or colon cancer in the stool. One such test, a fecal occult blood test, looks for blood in the stool that can not be seen with the naked eye (called occult blood), which could be coming from a bleeding polyp.

A stool DNA test, also known as FIT (fecal immunochemical test)-DNA test, is one in which the stool is tested for genetic material from a polyp or colon cancer.

Depending on the type of test used, screening should be repeated every one to three years.

Adenomatous Polyp Treatment

When an adenomatous polyp is found, it likely will be removed in order to prevent it from growing and becoming a risk for cancer.

Certain polyps may be more challenging to remove, especially if they are larger, flat, or are located behind a flap or fold in the colon.

After a polyp is removed, the tissue will be sent to the lab for an evaluation by a specialist known as a pathologist. The pathologist will look for signs of cancer or changes in cells that increase the likelihood of cancer in the future.

Polypectomy

Most adenomatous polyps will be removed through a procedure known as a polypectomy. Special tools on the colonoscope are used during a colonoscopy to remove polyps, including a wire loop. The loop might be used to snare the polyp at its base and remove it.

Sometimes this can result in bleeding, but it does not cause any pain, and in most cases, the bleeding will resolve. Serious complications after a polypectomy are not common.

Laparoscopic Surgery

If a polyp is too large to be removed during a colonoscopy, it might be necessary to use laparoscopic surgery to access it. This is also sometimes called minimally invasive surgery.

During laparoscopic surgery, small incisions are made in the abdomen (versus a large one in traditional surgery) to access the area where the polyp is located. Because the incisions are small, scarring is minimized and people often recover quicker than with open surgery.

Interpreting the Test Results

After a polyp has been examined by the pathologist, a pathology report will be issued to describe what was found based on a visual and microscopic evaluation.

Interpreting a pathology report can be difficult, but the findings may be easier to grasp once you get a basic understanding of the terminology. The findings are largely based on the type, location, and characteristics of the removed polyps.

Types of Adenomas

There are three types of adenomatous polyps, each of which has different growth patterns and potential for malignancy:

  • Tubular adenomas: This is the most common type that is typically small (less than 1/2 inch) and grows orderly like a row of test tubes.
  • Villous adenomas: This type is typically larger and has a more cauliflower-like appearance. These tend to grow quicker than tubular adenomas and have a greater potential for turning cancerous.
  • Tubulovillous adenomas: This is a type of polyp that share characteristics of both tubular and villous adenomas. They have a greater potential for turning cancerous than tubular adenomas but less than villous adenomas.

Location

The location of a polyp can contribute to the risk of colon cancer in several ways.

Firstly, certain locations make it harder to spot a polyp, meaning that it may go undetected until the malignancy is advanced. Secondly, there are locations in the colon where a polyp is more likely to recur (return) even after it has been removed.

The pathology report might refer to the polyp based on its location:

  • Adenomatous polyp of cecum: This is a polyp located at the junction between the small intestine and large intestine (colon). It is the structure situated furthest from the rectum and anus.
  • Adenomatous polyp of ascending colon: This is a polyp located in the first section of the colon adjacent to the cecum.
  • Adenomatous polyp of transverse colon: This is a polyp located in the longest and most movable part of the colon adjacent to the ascending colon.
  • Adenomatous polyp of descending colon: This is a polyp located in the part of the colon that extends from the traverse colon toward the rectum.
  • Adenomatous polyp of sigmoid colon: This is a polyp located in the final section of the colon between the descending colon and rectum.
  • Adenomatous polyp of distal colon: This is a polyp that occurs in any part of the cecum, ascending, or traverse colon.
  • Adenomatous polyp of proximal colon: This is a polyp that occurs in any part of the descending colon, sigmoid colon, or rectum.

Adenomatous polyps found in the distal colon are four times more likely to recur than those found in the proximal colon.

Polyp Characteristics

There are different terms that a pathologist will use to describe the physical or cellular characteristics of a polyp. These include:

  • Dysplasia: This describes how much a polyp looks like cancer under the microscope. It doesn't mean cancer but suggests that changes in cell structure and/or group are indicative of a risk based on the grade (severity) of the changes.
  • Hyperplasia: These are adenomas that are benign and have virtually no chance of becoming cancerous.
  • Pedunculated: This means that a polyp extends from the colon's wall with a stalk or stem, much like a mushroom.
  • Serrated: This means that the polyp tissues have a saw-toothed appearance under the microscope. A traditional serrated adenoma is a rare type more often found in the distal colon.
  • Sessile: This means that the polyp is slightly flattened and broad.

Sessile serrated adenomas and traditional serrated adenomas have an increased risk of turning cancerous.

Follow-Up

After an adenomatous polyp is found and removed, the next step is to discuss follow-up with the gastroenterologist. Although the overall risk may be small, all adenomatous polyps are risk factors for cancer.

The risk will depend on several factors, including how many polyps there were, how big they were, and what their characteristics were.

In most cases, follow-up screening will be advised. The interval will be based on current ACS/USPTF guidelines and other factors, such as your cancer risk.

A typical follow-up screening schedule might be:

  • One to two small polyps: A repeat colonoscopy in five to 10 years
  • More than two small polyps or large polyps: A repeat colonoscopy in three years
  • More than 10 polyps: A repeat colonoscopy in three years
  • Large polyps with a complicated removal: A repeat colonoscopy in six months

Summary

An adenomatous polyp, also known as adenoma, is an abnormal growth in the colon that tends to look similar to surrounding tissues. Most adenomas are benign but some can turn cancerous. Risk factors include older age, smoking, and a family history of polyps.

Adenomas are commonly found during a colonoscopy and will often be removed to check for signs of cancer in the lab. Removing polyps also reduces the risk of them turning cancerous.

Routine colon cancer screening is recommended starting from the age of 45. The screening should be repeated every one, three, five, or 10 years depending on the type of test used.

A Word From Verywell

There is not much that can be done to avoid adenomatous polyps. While risk factors such as age or race cannot be changed, living a healthful lifestyle may help reduce the risk of colon cancer.

Routine screening can also reduce the risk. A colonoscopy is considered the gold standard because it visualizes the entire colon and allows for the immediate removal of polyps if found. Removing a polyp means that it can’t continue to grow and become cancerous.

Don't let inconvenience or thoughts of discomfort sway you from getting a colonoscopy. It is a minimally invasive procedure whose benefits greatly outweigh the risks. Health insurance may also cover it as an Essential Health Benefit (EHB) of the Affordable Care Act (ACA).

Frequently Asked Questions

  • How serious are adenomatous polyps?

    Adenomas that are not removed continue to grow. As they get larger, the risk of cancer increases. That said, most adenomatous polyps are benign (non-cancerous) and harmless.

  • What percent of adenomatous polyps become cancerous?

    All adenomas are considered pre-cancerous. However, just 5% or fewer adenomatous polyps actually progress to cancer over the course of 10 years.

  • How do you prevent adenomatous polyps?

    You may not be able to prevent an adenomatous polyp from forming, but you can reduce your risk by living the healthiest lifestyle possible. This includes smoking cessation (if applicable), limiting alcohol intake, and preventing type 2 diabetes. Also talk to your healthcare provider about when and how often you should get screened for colorectal cancer.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.