Overview

What is a serrated adenoma or polyp?

Serrated polyps are a type of colon polyps that exhibit a serrated or saw-toothed look when viewed under a microscope. Colon polyps are noncancerous growths on the inner walls of the colon, which can develop into cancer over time. 

The bumpy texture of these polyps is connected to their growth patterns. Serrated polyps are created through a distinct process compared to adenomas, the more prevalent type of colon polyps. Serrated polyps transform into cancer through a different pathway from adenomas, and are the precursors for approximately 25% of colon cancer cases. 

Classifications of serrated polyp

The World Health Organization (WHO) has classified serrated polyps into four types. These categories are distinguished by their varying physical attributes. These traits indicate the different cellular processes that play a role in the growth of these polyps. Only some forms of serrated polyps have the potential to become cancerous. Healthcare providers categorize individuals when they detect them to anticipate their likelihood of developing cancer.^1,2

The four categories of serrated polyps:

1. Hyperplastic polyps
2. Sessile serrated lesions
3. Traditional serrated adenomas
4. Unclassified serrated adenomas

Hyperplastic polyps

Hyperplastic polyps make up around 75% of serrated polyps and are the most prevalent type. Hyperplastic polyps are non-cancerous and do not progress into cancer. The word "hyperplastic" refers to their formation due to an excessive growth of cells. Most precancerous polyps show signs of dysplasia, indicating a transformation of cells. These alterations in cells may result in cancer.

The following pathological features are usd to differentiate between the two types of HPs: mucin-vacuolated HP (MVHP) and goblet cell-rich HP (GCHP). MVHPs are more common than GCHPs. Before, the mucin-depleted type was seen as a distinct group; but now, it is known to result from regenerative changes in other HPs.

Sessile serrated lesions

Roughly 20% of serrated polyps belong to a category known as sessile serrated lesions (SSLs). These are the most frequently seen precancerous serrated polyps. The word "sessile" describes their flat or slightly raised form, which they share with their relatives, hyperplastic polyps. It may be difficult to differentiate them from hyperplastic polyps, but specialists can identify specific structural distortions.

Sessile serrated lesions were previously known as sessile serrated polyps and sessile serrated adenomas. The new name intends to minimize overall confusion. Furthermore, certain sessile serrated lesions exhibit signs of dysplasia, while others do not. Healthcare professionals also categorize these as sessile serrated lesions with dysplasia. However, they view all SSLs as potentially cancerous.

Traditional serrated adenomas

Traditional serrated adenomas are the least common form of serrated polyps, occurring in less than 1% of people. They are also in a precancerous stage. They have a similar appearance to regular adenomas, displaying a mushroom-like structure, dysplasia and serrated characteristics. In the past, these growths were frequently confused with typical adenomas. They were only acknowledged as a form of serrated polyp recently.

Unclassified serrated adenomas

Unclassified serrated adenomas have a mix of serrated and conventional polyp features, like serrated tubulovillous adenomas (sTVA) and superficially serrated adenomas. sTVAs have many ECFs but do not have eosinophilic cytoplasm or undulating serration. Genetically, sTVAs can experience a change in appearance as they gather genetic changes, shifting from a serrated pathway to a standard pathway.

The superficially serrated adenoma shows a surface lining with serrations and growing cells specifically found in the middle and lower sections of the mucosa. The WNT signaling pathway is activated in both the sTVA and superficially serrated adenoma.

Unclassified serrated adenoma

An unclassified serrated adenoma (USA) is a form of colorectal polyp that shows dysplasia and serrated structure but does not fit into the categories of the sessile serrated lesion (SSL), traditional serrated adenoma (TSA), or conventional adenoma.³

Causes

Colon polyps are common, especially as people age. While the exact causes of the genetic mutations that cause polyps are not fully understood, we know they are an important factor. Genetic mutations occur when cells make errors while copying their coding during replication, and may cause cells to develop abnormally. Various genetic changes result in serrated polyps, in contrast to other forms of colon polyps.¹

Risk factors

1. Over the age of 50
2. Tobacco use
3. Excessive consumption of alcohol
4. Frequent consumption of red meat¹
5. Excess body weight
6. Inflammatory bowel disease

Characteristics of unclassified serrated adenoma

1. Morphological features
   • Serration pattern: Unclassified serrated adenomas usually display a mix of characteristics seen in both serrated and traditional polyps, like serrated tubulovillous adenomas (sTVA) and superficially serrated adenomas²
   • Glandular architecture: These polyps often display a mix of epithelial and serrated architecture that makes them difficult to classify⁴
   • Cytological features: The cytological characteristics of unclassified serrated adenomas are not clearly defined; however, they generally display a mix of traits seen in both serrated and traditional polyps⁴
2. Immunohistochemical characteristics
   • Markers of serrated pathways: Specific markers like CDX2, GATA4, and GATA6 are expressed in the serrated pathway⁴
   • Other specific pathways: Additional markers like p53, Ki-67, and beta-catenin could also play a role in identifying and categorizing unclassified serrated adenomas⁴
3. Molecular profile 
   • Common genetic alterations: Unclassified serrated adenomas frequently display genetic mutations like KRAS, typically found in serrated adenomas²
   • Relationship to other serrated lesions: The connection between unclassified serrated adenomas, sessile serrated lesions, and traditional serrated adenomas is not fully understood²

Symptoms

Unclassified serrated adenomas (USAs) generally do not display distinct symptoms. The majority of individuals with USAs show no symptoms unless the growth exceeds 1 cm or develops into cancer. Possible signs and symptoms that could arise with urinary tract infections include:⁵

1. Stools with streaks of blood
2. Bleeding from the rectum
3. Altered bowel movements
4. Pain or discomfort in the abdomen

Nevertheless, these signs are not unique and can be present in many colorectal conditions. Most USAs are commonly discovered spontaneously during regular colonoscopy screenings.²

It is worth mentioning that the symptoms of USAs are not well described in the literature, as they are a newly identified and uncommon type of serrated polyps. Most research has been concentrated on the most prevalent serrated lesions such as sessile serrated adenomas and traditional serrated adenomas.³

Diagnosis

A colonoscopy is the most effective way to identify serrated polyps. However, they can sometimes be missed during the procedure. This is because the most prevalent forms of serrated polyps, such as hyperplastic polyps and sessile serrated lesions, have a subtle appearance. These polyps are typically small (approximately 5 millimetres), flat or slightly elevated ("sessile"), and matched in colour with the surrounding tissue, having indistinct boundaries.

More advanced colonoscopes with improved resolution and magnification are more effective in identifying serrated polyps than older models. Preparation and training are important as well. Healthcare professionals must stay informed about the latest recommendations for detecting serrated polyps. Providers have discovered that some bowel preparations for colonoscopy are more efficient than others and can impact visibility.

Although your doctor may suspect that a sessile serrated lesion or another type of precancerous serrated polyp is present during your colonoscopy, they may not always be able to confirm it. If there is suspicion, it will be taken out during the examination (polypectomy). They will forward it to a pathologist for examination in a laboratory, who will determine the exact type of polyp and provide the ultimate diagnosis.¹

Management

Dealing with unclassified serrated adenomas (USAs) requires the implementation of endoscopic therapy and monitoring techniques.

Endoscopic resolutions

Endoscopic removal is a common choice for treating unclassified serrated adenomas. Methods including cold biopsy forceps (CBF), cold snare polypectomy (CSP), and hot snare polypectomy (HSP) can be used to extract these polyps.³

Surveillance recommendation

Patients who have unclassified serrated adenomas might need frequent endoscopic monitoring to watch for any return or advancement. Surveillance guidelines for USAs are unclear but are expected to be akin to those for other serrated adenomas.²

Clinical and endoscopic characteristics

It is important to consider the clinical and endoscopic features of individuals with unclassified serrated adenomas when determining a treatment plan. These characteristics play a significant role in decisions regarding the type of endoscopic treatment and the frequency of surveillance required.³

Genetic and Molecular features

Understanding the genetic and molecular profile of unclassified serrated adenomas can provide valuable insights into their behaviour and potential for progression Molecular analysis could assist in determining risk levels and tailoring personalized treatment approaches.²

Prognosis

If your doctor removes precancerous serrated polyps during a colonoscopy you are temporarily protected, as eliminating them prevents the possibility of them developing into cancer. However, your healthcare provider will closely monitor your colon for several reasons. Sessile serrated polyps are difficult to completely remove by polypectomy due to their flat shape and unclear boundaries.

If any stray polyp cells remain following your polypectomy, or if smaller polyps were missed during your previous colonoscopy, they could progress into precancerous lesions. These may advance more rapidly than a completely new polyp. Moreover, serrated polyps tend to develop into cancer more quickly on average compared to other types. They are also at a higher risk of developing cancer simultaneously in multiple locations.¹

Summary

Serrated adenomas are a form of colon polyp with a saw-tooth appearance and the potential to grow into cancer. They account for 25% of colon cancer cases and are classified into four groups according to their physical characteristics. Risk factors include: being 50 years or older, using tobacco, drinking too much alcohol, eating a lot of red meat, being overweight, and having inflammatory bowel disease.

Identifying and eliminating during a colonoscopy is essential to prevent cancer. Management might require endoscopic extraction and monitoring. Comprehending serrated polyps is crucial for successful prevention and control of colorectal cancer.