Overview

Serrated polyps are a type of colon polyp which, when looked at under a microscope, have a sawtooth-like pattern. There are several types of serrated polyps, including hyperplastic polyps, sessile serrated lesions, and traditional serrated adenomas. These polyps are quite common and are usually benign. However, some of them are precancerous, meaning they can end up developing into colorectal cancer. In fact, 15% to 30% of colorectal cancer cases progress from serrated polyps.¹ Thus, serrated polyps have to be removed completely and are very important in colorectal cancer screening. 

Large intestine 

The digestive tract is a set of hollow organs that connect the mouth to the anus. It includes the mouth, oesophagus, stomach, small intestine, large intestine, and anus.

The large intestine is an organ that measures approximately 1.5 metres. It is a hollow muscular tube connected to the small intestine and is made up of the colon and the rectum. The colon can then be further divided into several sections: caecum, ascending colon, transverse colon, descending colon, and sigmoid colon. 

One of the main functions of the large intestine is to absorb the remaining water, nutrients, and vitamins from the waste leftover from the small intestine. While the waste is moved along the colon, gut bacteria break down the remaining nutrients and produce vitamins B and K which are then absorbed by the body. As a result it dehydrates and compacts the waste, forms it into stool, and moves it towards the rectum for elimination. 

Types of serrated polyps 

Serrated polyps are tissue growths that form on the inside walls of the colon in the large intestine. According to the World Health Organization (WHO) classification, serrated polyps are divided into four² different subtypes:

• Hyperplastic polyps are the most common serrated polyps, accounting for 70–90% of all serrated polyps. These polyps do not have the potential to develop into colorectal cancer.¹  They are usually smaller than 5mm in size.
• Sessile serrated lesions are the second most common serrated polyps and account for 5–25% of all cases.¹ These polyps have the potential to develop into colorectal cancer.^1,3 They are bigger in size, measuring more than 10mm. Sessile serrated lesions are more common in people assigned female at birth (AFAB) and usually appear in the caecum, ascending colon, or transverse colon.^1,3 
• Traditional serrated adenomas are the least frequent type of serrated polyps and account for 1% of all serrated polyps. These adenomas have the potential to develop into colorectal cancer. They usually develop in the descending colon or sigmoid colon and are bigger than 5mm in size.¹ 
• Unclassified serrated adenomas include serrated polyps that do not fit into the sessile serrated polyp, traditional serrated adenoma categories, nor conventional adenoma subtypes, because they have intermediate features.⁴ 

The different serrated polyp subtypes have different architecture when observed under a microscope. According to their different shapes, specialists can recognise each subtype. It is important to accurately diagnose the different types of lesions because they have different potentials for developing into cancer. 

Risk factors for serrated polyps

Several factors are associated with a higher risk of developing serrated polyps, including:

• Older age
• Family history of polyps and colorectal cancer
• Lifestyle factors such as obesity, cigarette smoking, alcohol intake, and inactivity⁶
• Medical conditions like diabetes⁷

Detection of serrated polyps

Serrated polyps are usually detected with a colonoscopy, which is an exam that consists of inserting a flexible tube with a camera attached into the rectum. The camera allows the specialist to look inside the large intestine and detect irritated tissue, polyps, and tumours. During a colonoscopy, a tissue sample, polyps, and abnormal tissue can be removed. 

Hyperplastic polyps and sessile serrated lesions are often difficult to detect because they have subtle features.⁵ Newer technologies are facilitating detection of polyps. Narrow band imaging colonoscopy has higher brightness and resolution which allows for higher definition images that help distinguish the different serrated polyp subtypes.⁸ Chromoendoscopy consists of using a contrast dye solution to visualise the inside walls of the colon to facilitate detection. Despite these newer technologies, up to 20% of polyps go undetected during a colonoscopy examination. 

During the last two decades, colorectal cancer screening programmes have been implemented worldwide. One of the screening methods consists of a non-invasive stool test like the faecal immunochemical test which detects the presence of human haemoglobin in the stool. However, because serrated polyps do not bleed a lot, faecal immunochemical testing is not ideal for polyp detection.⁹

Diagnosis of serrated polyps

It is possible to detect and diagnose serrated polyps based on their appearance in a colonoscopy. However, it is also possible to classify the removed polyps and biopsies in a laboratory since the different serrated polyp subtypes have different molecular features. As a result, testing for specific mutations can facilitate diagnosis. For instance, sessile serrated lesions have BRAF^V600E mutations. 

Management and treatment of serrated polyps

Since serrated polyps have the potential to develop into colorectal cancer, it is recommended that they are completely removed during a colonoscopy.¹⁰ This process is known as a polypectomy. By removing the serrated polyps, the risk of it developing into a colorectal tumour is eliminated. If a lesion is suspected to be a hyperplastic polyp, a biopsy is taken to rule out a precancerous polyp. In this case it is not necessary to remove the polyp.¹⁰ 

It is important to monitor patients with serrated polyps because of their potential to develop into colorectal cancer. Patients are currently recommended to do colonoscopies every 3 years for:

• Sessile serrated lesions bigger than 10mm in size,
• More than 3 sessile serrated lesions smaller than 10mm in size, or
• Traditional serrated adenomas of any size

Patients with smaller sessile serrated lesions should undergo colonoscopies every 5 years.¹¹ Lastly, patients with hyperplastic polyps are recommended to do colonoscopies every 5 or 10 years depending on the number, size, and location of polyps.¹²

Summary

Serrated polyps are tissue growths in the colon of the large intestine. The different subtypes of serrated polyps have different shapes and mutations associated. It is important to diagnose the specific subtype correctly, since sessile serrated lesions and traditional serrated adenomas have the potential to develop into colorectal cancer, whereas hyperplastic lesions do not develop into cancer. Polyps are usually detected with colonoscopy examination, and in most cases are completely removed so they do not develop into cancer. Since serrated polyps do not have any symptoms, it is important to follow recommended guidelines for routine colonoscopy check ups.  

FAQs

How common are serrated polyps?

It is difficult to accurately determine the prevalence of serrated polyps. It is estimated that between 13% and 35% of the population has some type of serrated polyps.¹³ 

What are the symptoms of serrated polyps?

Most serrated polyps don’t cause symptoms. Polyps do not usually bleed so it is hard to detect changes in the stool. This is why it is important to do routine colonoscopy screenings from the age of 45 onwards.

Can serrated polyps be prevented?

It is possible to reduce the risk of developing serrated polyps by making some lifestyle changes, such as not smoking cigarettes, reducing alcohol intake, and maintaining a healthy weight. Moderate exercise has also been shown to reduce the risks of developing serrated polyps.

Are serrated polyps cancerous?

No, serrated polyps are not cancerous. However, some serrated polyp subtypes like sessile serrated lesions and traditional serrated adenomas are precancerous, meaning they can develop into colorectal cancer. It is important that precancerous polyps are removed completely to prevent cancer development.

What is a sessile serrated lesion with dysplasia?

This is a subtype of sessile serrated lesion which is considered to rapidly progress into colorectal cancer. These polyps occur in 4–8% of cases of sessile serrated lesions.³ 

What is serrated polyposis syndrome?

It is a rare condition where patients have multiple serrated colorectal lesions throughout the large intestine.³ According to the WHO, patients are diagnosed with the syndrome when they have 5 serrated lesions or polyps bigger than 5mm, and 2 or more bigger than 10mm, or if a patient has 20 lesions of any size. Patients with serrated polyposis syndrome have a 25–40% higher risk of developing colorectal cancer.¹⁴ As a result, patients with the syndrome should undergo annual check ups. 

What is the difference between polyp and adenoma?

A polyp is the abnormal growth of tissue that bulges out from the surface of the organ. An adenoma is a specific type of polyp that comes from glandular tissue. An adenoma has a risk associated with developing cancer, whereas a polyp does not necessarily have a risk. 

When should I see a doctor?

Routine colonoscopies are recommended every 10 years from the age of 45 onwards. If there is a family history of colorectal cancer or polyps, colonoscopies might be done more often and starting at an earlier age.