Serrated Polyposis Syndrome (SPS) is defined by the development of multiple serrated polyps within the colon and rectum. This relatively rare disorder significantly increases an individual’s lifetime risk of developing colorectal cancer, with estimates ranging from 25% to 40% if not managed with intensive surveillance. The condition remains under-recognized due to the subtle nature of the polyps themselves. Unlike some other polyposis syndromes, SPS is generally not considered a classic inherited genetic disorder, but its presence signals a need for specialized medical management to prevent cancer progression.
Defining Serrated Polyposis Syndrome
Serrated Polyposis Syndrome is a clinical diagnosis, established based on the number, size, and location of the polyps found during a colonoscopy, rather than a specific single gene mutation. The overall prevalence of SPS is estimated to be low, occurring in about 0.03% to 0.5% of the general population.
The average age of diagnosis for SPS is typically around 55 years. While not a classic Mendelian inherited disease like Familial Adenomatous Polyposis (FAP), there is often a familial component, and a family history of SPS or colorectal cancer increases an individual’s risk. The specific cause of SPS is not fully understood, but it is thought to involve a combination of genetic predisposition and environmental factors, such as tobacco use.
The condition is serious because the polyps can progress to cancer through an alternative biological route known as the “serrated pathway,” which is distinct from the more common adenoma-carcinoma sequence. This pathway can sometimes lead to cancer more quickly than the traditional route. Because the polyps often do not cause any symptoms, the condition is usually discovered during routine screening colonoscopies.
Understanding Serrated Polyps
Serrated polyps are a distinct class of growths in the colon characterized by a saw-toothed appearance when viewed under a microscope. These polyps form through a different cellular process than traditional adenomatous polyps, which are the most common type of precancerous lesion. The World Health Organization (WHO) classifies serrated polyps into several types, but two are most relevant to SPS: Hyperplastic Polyps (HPs) and Sessile Serrated Lesions (SSLs).
Hyperplastic polyps are the most frequently encountered serrated lesion and are generally considered benign, with little potential for malignant transformation. They are often small and typically found in the distal colon. In contrast, Sessile Serrated Lesions are the primary concern in SPS and are definitively considered precancerous.
SSLs are known for their flat, subtle appearance, which makes them difficult to detect during a standard colonoscopy, especially if they are located in the proximal colon. These lesions progress to cancer via the serrated pathway, often involving specific genetic changes like the BRAF gene mutation. Histological distinction between HPs and SSLs can be challenging for pathologists, but it is a critical step because SSLs carry a significantly higher risk for cancer.
Establishing the Diagnosis
The diagnosis of Serrated Polyposis Syndrome is established through a meticulous clinical assessment, primarily relying on a high-quality colonoscopy and subsequent histological confirmation of the polyps removed. The current WHO criteria for an SPS diagnosis focus on the burden of polyps throughout the large bowel. A patient meets the diagnostic criteria if they satisfy one of the following:
- At least five serrated lesions located proximal to the rectum, with at least two measuring 10 millimeters or larger in size.
- More than 20 serrated lesions of any size distributed throughout the entire colon, provided at least five are located proximal to the rectum.
- Any number of serrated polyps proximal to the sigmoid colon in a person with a first-degree relative who has SPS.
Although SPS is not a classic inherited syndrome, genetic testing is often performed to rule out other polyposis conditions that might present with multiple polyps, such as MUTYH-associated polyposis. The diagnosis is cumulative, meaning the total number of serrated lesions found across multiple colonoscopies is counted toward meeting the criteria.
Long-Term Surveillance and Treatment
Once a diagnosis of Serrated Polyposis Syndrome is confirmed, the long-term management strategy shifts to intensive surveillance and treatment aimed at preventing colorectal cancer. The primary tool for both surveillance and treatment is a high-quality, meticulous colonoscopy, which must be performed by an expert endoscopist due to the subtle and flat nature of SSLs. Enhanced imaging techniques like narrow-band imaging or chromendoscopy may be used to improve the detection rate of these elusive lesions.
The goal of initial treatment is “polyp clearance,” which involves the complete removal of all significant serrated polyps, particularly those larger than 5 millimeters. Endoscopic mucosal resection (EMR) is often the preferred method for removing larger serrated lesions. Following the initial clearance, surveillance colonoscopies are typically recommended every one to two years.
The specific interval for follow-up depends on the polyp burden and whether the colon has been successfully cleared of large lesions. If the polyp burden is extremely high, if the polyps regrow rapidly, or if advanced dysplasia or cancer is found, surgical intervention may be considered. This surgery, typically a colectomy, removes a significant portion of the colon to eliminate the high cancer risk. Additionally, low-dose aspirin may be recommended as a chemopreventive measure, and lifestyle adjustments, such as cessation of smoking, are often advised to reduce the overall risk.