Serrated polyps are a class of colon polyps that your healthcare provider might discover during a colonoscopy. They’re common, and most are harmless, but some can be precancerous.
Serrated polyps are a class of colon polyps that have a serrated or saw-toothed appearance under a microscope. Colon polyps are benign tumors; tissue growths that develop on the inside walls of your colon. They’re not cancer, but some polyps, including some serrated polyps, can turn into cancer over time. Healthcare providers remove these types when they find them to prevent colon cancer from starting.
The serrated surface of these polyps is related to how they grow. Serrated polyps form by a different process than the more common type of colon polyps, called adenomas. When serrated polyps turn into cancer, it’s also by a different pathway than adenomas. Only about 25% of colon cancer cases develop from serrated polyps. But when they do, they may progress faster than the more common types.
The World Health Organization (WHO) has classified serrated polyps into four types. These types are defined by their different physical characteristics. These characteristics represent the different cellular processes involved in how these polyps grow. Only certain types of serrated polyps are precancerous. Healthcare providers classify them when they find them in order to predict their cancer risk.
Hyperplastic polyps are the most common type of serrated polyps, accounting for approximately 75%. Hyperplastic polyps aren’t harmful and don’t turn into cancer. The term “hyperplastic” means they develop simply from an overproduction of cells. Most precancerous polyps are “dysplastic,” which means the cells appear to actually transform. These cellular changes are what can lead to cancer.
Approximately 20% of serrated polyps are a subtype called sessile serrated lesions (SSLs). These are the most common precancerous serrated polyps. The term “sessile” refers to their flat or slightly elevated shape, although they share this shape with their cousins, hyperplastic polyps. They can be hard to distinguish from hyperplastic polyps, but experts can recognize certain distortions in their architecture.
Sessile serrated lesions have formerly gone by several other names, including sessile serrated polyps and sessile serrated adenomas. The new name is intended to reduce general confusion. Adding to their complexity, some, but not all, sessile serrated lesions show signs of dysplasia. Healthcare providers further classify these as sessile serrated lesions with dysplasia. But they consider all SSLs precancerous.
Traditional serrated adenomas are the rarest type of serrated polyps, found in less than 1% of the population. They’re also precancerous. They resemble traditional adenomas, with a mushroom-like shape and typical dysplasia, but they also have serrated features. Historically, these polyps were often mistaken for traditional adenomas. They’ve only recently been recognized as a type of serrated polyp.
The final category is for serrated polyps that can’t be clearly classified as one thing or the other. They may appear sessile and serrated but also have signs of dysplasia or features resembling adenomas. While these are rare, healthcare providers recognize that it’s important to identify these ambiguous polyps separately, as future research may reveal more about them. We’re still learning about serrated polyps.
Approximately 30% of routine colonoscopies discover serrated polyps. They’re usually harmless hyperplastic polyps, but up to 10% of them may be precancerous types, such as sessile serrated lesions. Healthcare providers conducting colonoscopies can’t always tell the difference during the exam. They might need to remove them and send them to a pathologist to examine under a microscope.
Serrated polyposis syndrome (SPS) is an uncommon disorder characterized by multiple serrated polyps throughout your colon. It was previously known as hyperplastic polyposis syndrome. You might have more than 20 polyps and/or they may be larger than average. They’re more likely to be precancerous types. This condition carries an estimated cancer risk of 25%. It occurs in roughly 0.4% of the population.
Most colon polyps, including serrated polyps, don’t cause symptoms. Rarely, large polyps may bleed or affect your bowel habits. Some people notice blood in their poop or develop unexplained diarrhea or constipation. But these symptoms are more likely to have other causes. Most people who have colon polyps won’t know it. That’s why healthcare providers recommend routine colonoscopy screenings.
Colon polyps in general are very common, especially as you get older. We don’t know all the reasons why they occur, but we do know that genetic mutations are involved. Genetic mutations are errors in the coding of your cells that occur when they replicate (copy). They cause the new cells to develop differently than they should. Different mutations cause serrated polyps, as opposed to other types of colon polyps.
Risk factors for serrated polyps are similar to the risk factors for colon polyps in general. They include:
A colonoscopy is the best method for detecting serrated polyps. But sometimes, they still go undetected. This is because the most common types of serrated polyps, both hyperplastic polyps and sessile serrated lesions, are relatively subtle in appearance. They tend to be small (around 5 millimeters), flat or just slightly raised (“sessile”) and the same color as the surrounding tissue, with vaguely defined borders.
Newer colonoscopes with higher resolution and magnification are better at detecting serrated polyps than older ones. Preparation and training also matter. Healthcare providers need to be up-to-date on current guidelines for identifying serrated polyps. Providers have also found that certain bowel preparations for colonoscopy are more effective than others and can make a difference in visibility.
Even though your provider may suspect a sessile serrated lesion or another precancerous type of serrated polyp during your colonoscopy, they won’t always be able to identify it for certain. If they suspect it, they’ll remove it during the exam (polypectomy). They’ll send it to a pathologist to examine it in a lab. The pathologist will identify the specific type of polyp it is and make the final diagnosis.
But your provider might recognize serrated polyposis syndrome during your colonoscopy. The criteria for diagnosing SSPs are based on the number and size of serrated polyps they find, as well as where they find them. Statistically, serrated polyps that are larger than usual or that appear in different parts of your colon than usual are also more likely to be precancerous types on close examination.
Hyperplastic polyps are common and aren’t a cause for concern. But if your provider suspects a precancerous type of serrated polyp, they’ll need to remove it. This is necessary both to confirm what type it is and to make sure it doesn’t progress to cancer. If it does turn out to be precancerous, your provider will want to schedule your next colonoscopy relatively soon, to make sure they don’t miss any new ones.
Healthcare providers classify the serrated polyps they find as low-risk, intermediate-risk or high-risk for colorectal cancer. They’ll recommend routine colonoscopy screenings based on this risk. Current guidelines recommend screening every five years for intermediate risk, every three years for high risk and every year if you have SPS. Low-risk hyperplastic polyps don’t require any special surveillance.
If your healthcare provider removes precancerous serrated polyps during your colonoscopy, you’re safe for now. Removing them removes the risk that they might turn into cancer. However, your provider will want to keep a close eye on your colon for several reasons. One reason is that because of their flat shape and vague borders, sessile serrated polyps can be hard to remove completely by polypectomy.
If stray polyp cells are left behind after your polypectomy, or if subtler polyps went undetected during your last colonoscopy, these may continue to develop into precancerous lesions. They may develop at a faster rate than an entirely new polyp would. In addition, serrated polyps may progress to cancer faster on average than other types. They’re also more likely to progress to cancer in multiple places at once.
If you’re at average risk, healthcare providers recommend routine colonoscopies every 10 years, starting at the age of 45. You might need one sooner if you have a biological family history of colon cancer or polyps, or if you have a health condition that statistically raises your risk of developing polyps, like inflammatory bowel disease. Ask your healthcare provider if you’re due for your routine colonoscopy screening for colon polyps.
A note from Cleveland Clinic
Like most colon polyps, serrated polyps are common and usually harmless. Some carry a small risk of becoming harmful over time. That’s what colonoscopies are for. As long as we’re checking for them and removing them when we find them, serrated polyps won’t have the chance to turn into cancer. We’re still learning about serrated polyps and how they behave, but we know enough now to treat them preventively.
Last reviewed by a Cleveland Clinic medical professional on 09/10/2023.
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