Serrated Polyposis Syndrome (SPS)

Key Points

  • Serrated Polyposis Syndrome (SPS) is a syndrome in which multiple hyperplastic or serrated polyps are identified in the large bowel.  
  • It is estimated that I in 3000 people may have this condition.  
  • This syndrome has been identified in recent years to be associated with an increased risk of developing bowel cancer. Other cancers are not usually associated with this syndrome apart from possibly pancreatic cancer at older ages.  
  • Regular bowel screening by colonoscopy ( with removal of polyps) can prevent bowel cancers developing  
  • Colonoscopy is usually performed yearly in the initial years after a diagnosis of SPS. This is to ensure that the polyps can be controlled by removal at colonoscopy. After a few years the interval between procedures may lengthen.  
  • Occasionally bowel surgery is required when polyps are multiple, large and show early signs of bowel cancer.  
  • Cigarette smoking is associated with increased polyp numbers.  
  • SPS is more common in individuals of European or Celtic descent   
    Up to 50% of individuals with SPS may have a family history of bowel cancer suggesting a possible genetic or inherited cause but this has not been confirmed. Genetic testing is not available.  
  • First degree relatives of individuals with SPS i.e. mother, father, sister, brother, children, have been shown in studies to have a 5 fold increase in their life time risk of developing bowel cancer when compared with the general population.  
  • First degree relatives also have an increased risk of developing SPS  
  • First degree relatives are advised to have 5 yearly bowel screening by colonoscopy from the from the age of 40 years or from an age 10 years younger than the youngest age at which bowel cancer or SPS was identified in the family.   
  • The aim of the NZFGICS is to reduce the number of cancers occurring in families by facilitating the required bowel screening


New Zealand has a high incidence of bowel cancer with approximately 6% of New Zealanders (1 in every 16) developing bowel cancer by the age of 75 years.  Most bowel cancer (90%)  occurs over the age of 50 years and in most individuals, it develops over a 5 to 10 year period from a particular type of bowel polyp - an adenoma.  A polyp is an outgrowth from the bowel but there can be various types of polyps.  The commonest classes of polyps are adenomas and serrated polyps.  

Approximately 20% of New Zealanders over 50 would be identified at colonoscopy to have a small adenoma-type polyp and 5% will have a serrated polyp.  The vast majority of these polyps will not go on to develop into bowel cancer, particularly if they are small in size and number and do not show advanced changes under the microscope.

Hyperplastic or serrated polyps have been recognized for many years. Commonly a few small (less than 5mm) hyperplastic polyps are seen in the lower bowel - the rectum or back-passage – and have been considered to be of no concern.  Some serrated polyps may progress to bowel cancer and this risk is increased if hyperplastic or serrated polyps are present throughout the whole large bowel – not just in the rectum. On the basis of their appearance under the microscope, serrated polyps have been sub-categorized to try and identify the types of serrated polyps that may be associated with progression to bowel cancer. Often more “advanced” serrated polyps occur in the proximal large bowel or right side of the colon, and may be quite flat and difficult to find during colonoscopy.  

A diagnosis of Serrated Polyposis Syndrome (SPS) is made when an individual has over 20 serrated polyps throughout the colon, or where there are at least five serrated polyps but two are large - 10 mm or more in size.  Sometimes, during a colonoscopy performed for another indication, there may be a suspicion that a diagnosis of SPS is likely but there aren’t that many polyps.  For this reason in making a diagnosis of SPS, we add up the number of polyps removed over several colonoscopies.  

Approximately 30 to 50% of patients with SPS present with bowel cancer but we are uncertain just how many of the 1:3000 people in the population with SPS will develop bowel cancer. Risk factors for developing cancer are being identified, and in some a 30% lifetime risk of bowel cancer has been estimated. Work to better define these risk factors is ongoing but a number of studies have already documented that SPS patients undergoing frequent colonoscopy with polyp removal are much less likely to develop bowel cancer.  Colonoscopy is usually offered every one to two years, once ‘control’ of the polyps has been achieved - in other words when there aren’t many polyps developing in between colonoscopy procedures. Sometimes colonoscopy may be performed more frequently in the first few years to ensure all the larger polyps are removed.   Serrated polyps can be very hard to detect during colonoscopy because even when large, they are very flat and often have a mucous cap hiding them.  It is therefore very important that when you present for colonoscopy your bowel is as clean as possible - this gives the endoscopist the best chance of finding these polyps.  For this reason it is important that you strictly follow the bowel preparation instructions provided to you before your colonoscopy and if you notice that you are still passing brown or murky stool before you are due to arrive for the colonoscopy, call ahead to see if an enema or more preparation can be offered to help clear your bowel completely.

If SPS patients have new bowel symptoms between colonoscopies like bleeding from the back passage; or their bowel pattern becomes more frequent; or their stool becomes consistently looser; or they develop unexplained abdominal pain, they should discuss this with their doctor promptly.

On occasions it is not possible to remove all the bowel polyps at colonoscopy because they are too big, too numerous or polyp biopsies show that they have already developed advanced features. In these situations a small percentage of patients with SPS may be advised to have bowel surgery.  This does not usually involve a permanent stoma (colostomy/ileostomy).  

A genetic predisposition to developing SPS is suspected because up to 50% of individuals with SPS may have a family history of bowel cancer. It is possible that SPS may be “weakly inherited” requiring a number of minor genetic predispositions, from both parents, to be inherited together. SPS is certainly much more common in individuals of European or Celtic descent.  

Genetic “spelling mistakes” – or mutations – have been reported in the RNF43 gene in several SPS patients, although these reported RNF43 variants do not account for the majority of people with SPS.  Multi-gene panel testing in people with confirmed SPS very rarely identifies a mutation that helps make a diagnosis or that changes management advice.

We are involved in a study seeking to identify the genetics associated with this condition and if you were diagnosed with the Serrated Polyposis Syndrome under the age of 70y, you may be offered involvement in this study.

First degree relatives (mother, father, siblings or children) of individuals with the Serrated Polyposis Syndrome have been shown in studies to have a five-fold increase in their lifetime risk of developing bowel cancer when compared to the general population.  For this reason, it is recommended that first degree relatives (i.e. father, mother, sister, brother or children) be offered screening by colonoscopy every five years, from 10 years younger than the earliest age at which SPS was diagnosed in the family, but no later than age 40.  If first degree relatives have any concerning bowel symptoms, like bleeding from the back passage, persistent diarrhoea or unexplained abdominal pain, they should discuss this with their doctor promptly.

Smoking increases the number of both adenomatous and hyperplastic polyps but it appears to particularly increase the number of serrated polyps.  We recommend avoiding smoking for this reason.  

There are no known means by which one can reduce the development of serrated-type polyps, but we recommend a standard healthy diet, maintenance of ideal body weight, and regular exercise.  The Ministry of Health has produced a helpful eating and activity guidelines available on their website: