Serrated polyposis syndrome (SPS), previously known as hyperplastic polyposis syndrome, is a disorder characterized by the appearance of serrated polyps in the colon. While serrated polyposis syndrome does not cause symptoms, the condition is associated with a higher risk of colorectal cancer (CRC). The lifelong risk of CRC is between 25 and 40%. SPS is the most common polyposis syndrome affecting the colon, but is under recognized due to a lack of systemic long term monitoring. Diagnosis requires colonoscopy, and is defined by the presence of either of two criteria: ≥5 serrated lesions/polyps proximal to the rectum (all ≥ 5 mm in size, with two lesions ≥10 mm), or >20 serrated lesions/polyps of any size distributed throughout the colon with 5 proximal to the rectum.A family history of SPS and smoking tobacco are associated with a higher risk of serrated polyposis syndrome, whereas the use of aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) are associated with a lower risk. While the only validated genetic cause of SPS is RNF43, additional important genetic abnormalities include BRAF mutations, abnormal CpG island methylator phenotype, and microsatellite instability. However, most individuals with the syndrome do not have an associated germline mutation. The types of polyps found in SPS include sessile serrated adenomas/polyps, traditional serrated adenomas, and hyperplastic polyps. SPS occurs in 2 phenotypes: proximal and distal. Proximal SPS has a greater risk of CRC than distal SPS. The vast majority of cases may be managed with colonoscopy with removal polyps (polypectomy).
Polyp removal is recommended to decrease the risk of colorectal cancer. Repeat colonoscopy should be performed every 1–2 years. If polyps are very large, numerous, or increase in number rapidly, then surgery may be necessary. Surgery may also be warranted if CRC is suspected or confirmed. First-degree relatives of people with SPS have an increased risk of CRC, and should undergo early screening with colonoscopy. Types
SPS may occur with one of two phenotypes: distal or proximal. The distal phenotype may demonstrate numerous small polyps in the distal colon (sigmoid) and rectum, whereas the proximal phenotype may be characterized by relatively fewer, but larger polyps in the proximal colon (cecum, ascending colon, etc.). Individuals meeting only criterion 3 from 2010 criteria, or only criterion 2 from the 2019 classification, have a distal phenotype have a lower risk of CRC compared with the proximal phenotype. Signs and symptoms
Serrated polyposis syndrome often does not cause symptoms. The risk of colon cancer is between 25 and 40%.Sessile serrated polyps, as seen during endoscopy or colonoscopy, are flat (rather than raised) and are easily overlooked. Serrated lesions range in size from small (<5 mm) to large, and often have a "mucous cap" overlying the polyp. Serrated lesions are frequently located on the folds of the colon (haustral folds). Pathophysiology
SPS is not caused by a single gene mutation. Several genetic abnormalities are associated with the condition, and a familial or inherited pattern may occur. Key genetic abnormalities include mutations in BRAF, abnormal CpG island methylator phenotype, and microsatellite instability.