Colon Polyp Size Chart to Gauge Risk
Medically reviewed by Jay N. Yepuri, MDMedically reviewed by Jay N. Yepuri, MD
Polyps in the colon and rectum (together called colorectal polyps) are common in people over age 50. They are usually noncancerous, but certain characteristics can increase the likelihood of a polyp becoming cancerous.
The risk of a polyp becoming cancerous increases with size. Polyps that are 10 millimeters (mm) or larger are considered to have a higher cancer risk than ones that are smaller than 10 mm.
This article will discuss the sizing of colon polyps, what size colon polyps could be cancerous, the implications of multiple colon polyps, how soon after a colonoscopy you learn polyp size, and the next steps in knowing the size of a colon polyp.
Illustration by Zoe Hansen for Verywell Health
Sizing Chart for Different Colon Polyps
Colorectal polyps are categorized into three sizes:
Diminutive | 5 mm or less |
Small | 6 mm to 9 mm |
Large | 10 mm or more |
Polyps that are found to be more than 30 mm (3 centimeters (cm)) on endoscopy (a procedure that uses a flexible tube to explore the digestive tract) can be labeled giant polyps.
Colorectal polyps are also classified by other important characteristics.
Polyps can be divided into four shape categories:
Pedunculated | Ball of tissue that is attached by a "stalk" (like a mushroom, or broccoli floret) |
Flat | No visibly raised portion; Often hard to see |
Smooth bump or gradually sloping "hill" | |
Depressed | Small depression or "dip" in the lining of the colon; Rare |
Colorectal polyps can be categorized by type, including:
Adenomatous (Tubular Adenoma) | Most common type; Most cancerous polyps begin as adenomatous (but only a small percentage of adenomatous polyps become cancerous); Generally, the larger the polyp, the more risk for it to become cancerous |
Villous Adenoma/ Tubulovillous Adenoma | Commonly sessile in shape; High risk of becoming cancerous; Account for about 15% of polyps detected in colon cancer screening (tubulovillous adenomas along with villous adenomas); Smaller polyps may be removed during a colonoscopy; Larger polyps may require surgery; Can be difficult to remove |
Serrated Adenoma | Can be flat; Can be larger; Difficult to detect; Precancerous; Account for 10% to 15% of polyps; Cause 20% to 30% of colon cancers |
Hyperplastic | Type of serrated polyp; Common; Small; Extremely low risk for becoming cancerous |
Inflammatory | Also known as pseudopolyps (not true polyps); Develop as a reaction to chronic inflammation in the colon; Most commonly occur in people who have inflammatory bowel disease (IBD); Generally not a risk for becoming cancerous |
Malignant | Contain cancerous cells |
What Are Complex Polyps?
Complex polyps (also called defiant polyps) have one or more of the following features:
Bigger than 20 mm (2 cm)
In a location that is unfavorable for removal by more straightforward techniques
Too sessile for removal by more straightforward techniques
Seemed unsafe to remove during the colonoscopy (as determined by the healthcare provider performing the procedure)
What Colon Polyp Size Could Be Cancerous?
Having a colorectal polyp doesn't necessarily mean cancer will develop. Most polyps do not become cancerous, and it can take years for the polyps that do to become cancerous.
In addition to the type of polyp, the characteristics typically focused on to determine the potential cancer risk of a polyp include:
Size: How big the polyp is
Number: How many polyps are there, particularly precancerous ones
Histology: How the polyp's cells appear under a microscope (shape, how they grow, abnormalities). If cells look abnormal but are not yet cancerous, it is called dysplasia.
Cancer risk is not determined by size alone, but the size of the polyp is an important consideration.
Cancer develops when mutations occur in quickly dividing cells. Cells that contain an error in their DNA continue to divide and replicate, where the chance for more errors can occur. These errors, accumulating over time, can lead to cancer. A large polyp has been around longer and is made of larger masses of cells, so the opportunity for cancer to develop through these cellular changes is higher. Multiple polyps also create more opportunities for errors to occur.
In general terms, colorectal polyps that are 10 mm (1 cm) or bigger in diameter are considered to have a higher risk of becoming cancerous than those smaller than 10 mm. Adenomas and sessile serrated polyps that are 10 mm or more are classified as advanced.
The risk that a polyp will become cancerous can continue to rise with the size of the polyp. Depending on the type and other factors, up to 50% of polyps over 20 mm (2 cm) are cancerous.
Some research has found that the incidence of polyp cancer is up to 75% when a polyp reaches 35 mm (3.5 cm).
Other considerations can influence these risks. For instance, Tubular adenomas are associated with cancer in about 5% of cases, while the rate for villous adenomas can be up to 40%.
Some research has found the risk of a polyp becoming cancerous is particularly high when adenomas:
Are large (10 mm or more)
Are multiple
Have a villous pathology
Research findings have also suggested that advanced adenomas progress to cancer at a higher rate than the average rate for all adenomas, and this advanced rate increases with the age of the person. Advanced adenomas are defined as having at least one of these criteria:
At least 10 mm in size
Villous architecture of at least 25%
High-grade dysplasia
Though polyps 10 cm or larger in size carry a higher risk of cancer, most adenomas (60% to 75%) detected with colonoscopy are smaller than 10 cm.
Smaller polyps are still routinely removed during colonoscopies.
Implications of Multiple Colon Polyps
The number of colorectal polyps has several implications.
The number of polyps can affect the recommendations for future screening, particularly in conjunction with other factors such as size. For example, if there are three to four small polyps, a follow-up colonoscopy may be suggested for three years, whereas the presence of five or more small polyps may prompt a recommended repeat colonoscopy in a year.
The risk of cancer development can increase with multiple polyps, as well as the risk of developing more polyps in the future, with more than 10 adenomas considered the highest risk.
Certain conditions, called polyposis syndromes, are associated with multiple polyps. These include:
MUTYH-associated polyposis (MAP)
Peutz-Jeghers syndrome
Juvenile polyposis syndrome
Serrated polyposis syndrome (SPS)
PTEN hamartomatous tumor syndromes
Hereditary mixed polyposis syndrome (HMPS)
Cronkhite-Canada syndrome
The characteristics, causes, and risks of cancer development vary by condition. FAP typically causes hundreds of colon polyps, and people with this condition have nearly a 100% chance of developing colorectal cancer, usually by the time they reach age 50.
Other Risk Factors for Colorectal Cancer
Risk factors for colorectal polyps and/or colorectal cancer include:
Age (most cases are in people 45 years and older, and incidence increases with age)
Ethnicity (higher rates of colorectal cancer in Black adults and American Indian and Alaskan Native adults)
Diabetes
Personal and/or family history of polyps or colorectal cancer
Rare, inherited genes or conditions that increase the likelihood of developing polyps
An inflammatory bowel disease
A high-fat, low-fiber diet
Tobacco and/or alcohol use
Obesity
Little or no regular exercise
How Soon Do You Learn Colon Polyp Size After Colonoscopy?
If a polyp is found during a colonoscopy, the medical professional (typically an endoscopist) will measure the polyp during the procedure.
Colorectal polyps are usually removed during the colonoscopy unless they can not safely be taken out at that time. The polyp is then sent to a lab to be examined by a pathologist. The pathologist will measure the polyp for size and check for other factors, such as if:
It was completely removed
There are any cancerous changes in the polyp
There is a risk that it will regrow
Results from the colonoscopy are typically available within five to seven business days, sometimes sooner, but this timeline can vary by provider. Check with your healthcare provider about when you should book a follow-up appointment or when you can expect to hear back about your results.
Next Steps: Determining the Size of a Colon Polyp
If a polyp or other abnormality was found on a screening test, more tests may be necessary, including a colonoscopy if one has not already been performed.
It isn't possible to know if a polyp will become cancerous, so polyps are usually removed. This is typically done during the colonoscopy, using simple devices such as forceps or snares, introduced through the scope.
If the polyp or polyps are of abnormal size or in areas that are difficult to access, they may require more specialized procedures to remove or treat them, including:
Endoscopic mucosal resection: Special instruments lift the abnormal tissue and trap the polyp in a small rubber band. Another tool then cuts the polyp from the colon. If necessary, the process is repeated to remove all abnormal tissue.
Endoscopic submucosal dissection: Small amounts of fluid are injected, creating a cushion between healthy tissue and the base of the polyp. Large, complicated polyps are then slowly and carefully removed in one piece.
Argon plasma coagulation: Ionized argon gas delivers thermal energy (plasma). This can help destroy fragments of abnormal tissue after a polyp is removed.
Rarely, surgery to remove the part of the colon that contains the polyp(s) (called a partial colectomy) may be necessary if the polyp(s) are very likely to become cancerous or are too large to remove during the colonoscopy.
If polyps are found and removed during a colonoscopy, there is a 25% to 30% chance that polyps will be found in future colonoscopies as well. This means your healthcare provider may suggest you have another colonoscopy sooner than the 10-year interval suggested if no polyps are found.
Factors that help determine the best course of action after polyps are found and when the next colonoscopy should be performed include:
Type, size, number, and location of the polyp(s)
Microscopic characteristics of the polyp(s)
Whether it was possible to examine the entire colon (such as if the bowel preparation to remove feces before the colonoscopy was adequate)
Presence of other risks for polyps and/or colorectal cancer (such as family history)
Age and general health
It is very important to follow the directions of your healthcare provider in terms of follow-up to your colonoscopy and any further testing or treatments. Early detection and removal of colorectal polyps can reduce your chances of developing colorectal cancer.
Summary
The size of a colorectal polyp is one of several important factors in determining the risk of the polyp becoming cancerous. Generally speaking, polyps 10 mm or bigger are more likely to become cancerous than those smaller than 10 mm, but this can vary depending on other characteristics, such as the type of polyp.
Most polyps are removed during the colonoscopy. They are then examined by a pathologist.
Some harder-to-remove polyps may require more specialized procedures.
If one or more polyps are found, another colonoscopy is usually recommended before the standard 10-year intervals suggested when no polyps were found. Listen to your healthcare provider and follow their directions for follow-ups and further testing.
Routine testing for polyps and colorectal cancer, as well as proper follow-ups, are very important because early detection and removal of polyps can decrease the risk of the development of colorectal cancer.
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