Colon polyps are small growths on the lining of your large intestines and rectum.

Doctors classify colon polyps based on factors such as their size, location, and appearance. These classifications help doctors determine their risk of becoming colorectal cancer. Knowing what type of polyps you have can also help your doctor determine the best way to manage them.

Precancerous adenomas are considered to be the most dangerous of the polyps. Smaller polyps have a lower chance of developing into cancer.

You can learn about the risk factors associated with the different classifications of polyps by reading this.

Illustration showing colon polyp sizes and risk factors
Illustration by Yaja’ Mulcare

The size of a colon polyp is related to the chance of it turning into cancer. Doctors use the size of the polyp to decide how to manage it.

Neoplastic polyps are polyps that have the potential to become cancerous. According to 2016 research, they are considered advanced if:

  • They are at least 10 millimeters in diameter.
  • Precancerous changes are visible in their cells.
  • They are classified as tubulovillous adenomas.

Advanced adenomas have a 5 percent annual risk of developing into cancer, and the risk increases as you get older. By age 55, the risk is 25 percent per year, and by age 80, the risk rises to 40 percent.

Here’s how experts classify polyps by size:

Size Diameter in millimeters Description
diminutive less than 5 They make up about 75% of all polyps, according to a 2020 review, and rarely progress into colorectal cancer. Only about 1–2% of diminutive adenoma polyps have advanced features.
small 6–9 About 7–12% of small adenoma polyps show advanced features.
large more than 10 Large polyps have the highest chance of becoming cancerous, with 20–30% of large adenomas showing advanced features. They have a 3% annual risk of becoming cancer.

The three main classifications for polyps are:

  • Adenomas is also called adenomatous polyps.
  • hyperplastic and inflammatory polyps
  • There are two types of adenomas, traditional and serrated.

The risk of becoming cancer is highest for adenomas. Depending on their appearance, adenomas are classified as tubular, villous, and tubulovillous.

Inflammation and hyperplastic polyps are not usually cancer causing.

A 2016 review suggests all neoplastic polyps should be removed to lower cancer risk. Neoplastic polyps include adenomas and serrated adenomas. Doctors generally recommend removing any polyps found during a bowel examination to lower the risk of any of them becoming cancerous.

Years ago, the U.S. National Polyp Study found that having a clean colon where all adenomatous polyps have been eliminated significantly decreased the odds of developing colorectal cancer. In addition, a recent study found that follow-up screening (colonoscopies) after the removal of adenoma polyps is associated with a lower incidence of colorectal cancer.

The National Health Service says that colon polyps affect as many as 1 in 4 people over 50 years old. Most polyps do not turn into cancer, but some can.

Experts believe that most bowel cancers develop from polyps classified as adenomas.

Most colon polyps don’t cause any symptoms and are usually found when examining your bowel for another reason or during screening for bowel cancer. If symptoms do develop, they can include:

The majority of colorectal cancers begin as colon polyps. According to a 2016 review, the risk factor most related to the development of colorectal cancer is the total number of adenoma polyps in your bowel. The ACS says women in the United States have about a 1 in 23 chance of developing colorectal cancer in their lifetime. Men have about a 1 in 25 chance.

Colon cancer risk factors

Many of the risk factors for developing colon cancer are lifestyle habits that you can modify. According to the Centers for Disease Control and Prevention (CDC), these include:

  • There is no physical activity.
  • Diet low in vegetables and fruit.
  • A diet high in processed meats has low fiber and high fat.
  • tobacco use
  • high alcohol consumption
  • Having a body mass index over 30

Some risk factors are out of your control.

Precancerous growths are found before colon cancer is diagnosed. It can help you detect cancer in the early stages.

The U.S. Preventive Services Task Force recommends:

Age Recommendation Level of evidence
45 to 49 All adults should be screened. moderate
50 to 75 All adults should be screened. high
76 to 85 Some people should be screened depending on overall health and prior screening history. moderate

The National Cancer Institute says methods suitable for colon cancer screening include:

Polyps are growths in the colon. Doctors classify colorectal cancer-causing polyps based on size and type.

Polyps that are classified as adenomas should be removed. Smaller polyps have a lower chance of becoming cancer.

If you are screened regularly, you can catch colon cancer in the earliest stages, and adenomas before they become cancer.

The U.S. Preventive Services Task Force recommends that all adults are screened for colon cancer. If you are between the ages of 75 and 85, it is a good idea to talk with a doctor to find out if you should be screened.