Colon polyps are a collection of cells that grow in the colon. They can vary in size and shape. Colon polyps can be benign, but larger colon polyps may have an increased risk of developing into colorectal cancer.

A tool used in a colonoscopy to detect the size of colon polyps -2.Share on Pinterest
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The size of colon polyps matters as small polyps may be harmless, but larger polyps may have a higher risk of being cancerous.

There is no specific size at which a polyp becomes cancerous, but healthcare professionals consider a polyp to be advanced when they reach 1 centimeter (cm) in diameter.

This article examines the cancer risk associated with the size of colon polyps. It also looks at the different types of colon polyps, their shape and growth patterns, and when a person should undergo screening for colorectal cancer.

The following infographic shows the size of colon polyps and how that can relate to cancer:

An infographic showing the size of colon polyps.Share on Pinterest
Medical Illustration by Yaja’ Mulcare

Healthcare professionals classify polyps by size using the following categories:

Colon polyp sizeDiameterCancer risk
Diminutive5 mm or less.The risk of cancer is low. A 2020 article notes that 75% of all polyps are diminutive and rarely develop into colorectal cancer.
SmallBetween 6 and 9 mm.The risk of cancer is low. A 2017 study found no cancer present in 6,523 small polyps.
Large1 cm or more.The cancer risk may be higher in larger colon polyps. Doctors refer to polyps over 1 cm as advanced, and people may need a follow-up sooner than for smaller polyps.

Learn more about colon polyp sizes and cancer risk.

There are different types of colon polyps, and each type may have a different cancer risk. The types of colon polyps and their cancer risk are as follows:

DescriptionCancer risk
InflammatoryInflammatory polyps may occur with inflammatory bowel disease (IBD).Inflammatory polyps are unlikely to become cancerous, but IBD does increase colorectal cancer risk.
HamartomatousHamartomatous polyps may occur in people with certain genetic conditions, such as Peutz Jaeghers, Cowden syndrome, or juvenile polyposis.Hamartomatous polyps are unlikely to become cancerous.
If people have a polyposis syndrome, the polyps may have a risk of colorectal cancer.
HyperplasticHyperplastic polyps are common and usually occur in the distal colon.Hyperplastic polyps on the right side of the colon may have a cancer risk.
If they do not occur due to a hereditary condition, the cancer risk is generally low.
AdenomasAdenomas account for around two-thirds of colon polyps.Adenomas are precancerous.
Sessile-serrated and traditional-serratedSessile-serrated and traditional-serrated polyps get their name from their rough borders.Sessile-serrated and traditional-serrated polyps are precancerous.

Learn more about different types of colon polyps.

Colon polyps grow slowly, and a small colon polyp may take up to a decade to form.

They may appear flat or depressed. They may also be sessile or pedunculated:

  • Pedunculated: Pedunculated polyps grow on a narrow stalk, like a mushroom.
  • Sessile: Sessile polyps do not have a stalk and are flat against the colon wall.

Both of these types of polyps may develop into noncancerous, precancerous, or cancerous polyps.

Adenomas, which account for around 66% of colon polyps, are a type of precancerous polyp and have the following growth patterns:

  • Tubular growth pattern: These are smaller adenomas that grow in a tubular shape and measure less than half an inch.
  • Villous adenoma: These are larger adenomas that grow in an uneven, cauliflower-like pattern.
  • Tubulovillous adenoma: These adenomas have the growth pattern of both tubular and villous adenomas.

The type of growth pattern may determine how regularly people will need a colonoscopy. An adenoma may take around 10 years to become cancerous, although this may be earlier if people have a hereditary syndrome.

According to the American Society for Gastrointestinal Endoscopy (ASGE), the usual procedure is to remove any polyps found through screening.

Doctors will generally perform a colonoscopy to remove a polyp, which they may be able to do in the same procedure as the screening. A colonoscopy can remove almost all precancerous polyps found through screening.

Removing polyps can eliminate the risk of them developing into cancer. Without removal, a polyp may cause bleeding, bowel obstruction, or may become cancerous.

The recommended screening guidelines for colon polyps for those with an average risk of colorectal cancer are as follows:

  • Colorectal cancer screening begins at age 45 and continues regularly until age 75.
  • For those ages 75–85 years, screening will depend on previous screening, personal preference, overall health, and life expectancy.
  • For those over the age of 85, colorectal cancer screening will stop.

People with a higher risk of colorectal cancer may need to begin screening earlier than age 45 or attend more regular screenings.

People can talk with a healthcare professional about their risk factors for colorectal cancer and how often they will need screening.

Colon polyps may not cause any symptoms, and a doctor may identify them through colorectal cancer screening. If colon polyps do cause symptoms, they may include:

The following are common questions about colon polyp size and cancer risk.

What size of colon polyp is concerning?

According to a 2019 study, the risk of cancer occurring in polyps less than 5 millimeters (mm) may be very low. The study examined 15,906 polyps.

In polyps larger than 30 mm in size, 4.3% of polyps were cancerous. The researchers found no cancer present in polyps smaller than 5 mm.

What size are most cancerous polyps?

According to the National Cancer Institute, the risk of colorectal cancer increases in relation to the size of the colon polyp. Between 30–50% of polyps larger than 2 cm are cancerous.

The risk of colorectal cancer may increase with larger polyps and certain types of polyps. Doctors classify colon polyps by size, shape, and growth pattern.

Polyps may not cause any symptoms, so attending recommended screenings is important. If a doctor finds a polyp, they may be able to remove it in the same procedure as the screening.