Colon polyps are small growths in the intestine and rectum that can become cancerous. Colon polyp size can help your doctor assess your cancer risk. Larger polyps are more likely to become cancerous than smaller ones.

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.

Most polyps never become cancer, but polyps classified as adenomas are considered precancerous. Larger polyps tend to have a higher chance of developing cancer than smaller ones.

Keep reading to learn about how polyps are classified based on their size and type, and the risk factors associated with these classifications.

Illustration showing colon polyp sizes and risk factorsShare on Pinterest
Illustration by Yaja’ Mulcare

The size of a colon polyp generally correlates with its chances of turning into cancer. Doctors often use the size of the polyp to determine the best way to manage it.

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

  • they’re at least 10 millimeters in diameter
  • their cells show precancerous changes
  • they’re classified as villous or 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:

SizeDiameter in millimetersDescription
diminutiveless than 5They 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.
small6–9About 7–12% of small adenoma polyps show advanced features.
largemore than 10Large 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:

  • adenomatous polyps, also called adenomas
  • hyperplastic and inflammatory polyps
  • sessile serrated adenomas (SSAs) and traditional serrated adenomas (TSAs)

Adenomas and serrated adenomas have the highest risk of becoming cancerous. Scientists further classify adenomas as tubular, villous, and tubulovillous depending on their appearance.

Inflammatory and hyperplastic polyps rarely become cancerous.

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:

  • lack of physical activity
  • diet low in fruit and vegetables
  • low fiber and high fat diet or diet high in processed meats
  • tobacco use
  • high alcohol consumption
  • having overweight or obesity

Some risk factors are out of your control or mostly out of your control, such as:

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Regular screening for colon cancer is critical for discovering precancerous growths before they turn into cancer. It can also help you detect cancer in the early stages when it’s easiest to treat.

The U.S. Preventive Services Task Force recommends:

AgeRecommendationLevel of evidence
45 to 49All adults should be screened.moderate
50 to 75All adults should be screened.high
76 to 85Some 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 irregular growths in your bowel. Doctors often classify polyps based on size and type to determine their risk of becoming colorectal cancer.

Polyps classified as adenomas are considered precancerous and should be removed. Larger polyps have a higher chance of becoming cancer than small polyps.

Regular colon cancer screening gives you the best chance of catching adenomas before they become cancerous or catching colon cancer in the earliest stages.

The U.S. Preventive Services Task Force recommends that all adults between 45 and 75 years old get screened for colon cancer. If you’re between the ages of 75 and 85, it’s a good idea to talk with a doctor to find out if you should be screened.