Serrated polyposis syndrome: diagnosis, bowel cancer risk and surveillance

The NHS describes bowel polyps as small growths on the lining of the large intestine or rectum that are very common and not usually serious, although sometimes they can lead to bowel cancer. Most people with polyps will have no symptoms and will not know they have them. Polyps come in different types. Serrated polyps are those with a saw-toothed appearance under the microscope, according to NHS England's genomics education programme.

Having a single serrated polyp does not mean serrated polyposis syndrome. The syndrome is defined by having many such polyps, of a particular size and distribution, and carries a higher risk of bowel cancer than having the occasional polyp.

SPS is a clinical diagnosis. The 2019 updated World Health Organization criteria, as summarised in the NHS England genomics resource, are at least five serrated lesions or polyps proximal to the rectum, all 5mm or greater in size with two or more 10mm or greater; or more than 20 serrated lesions or polyps of any size distributed throughout the large bowel, with at least five proximal to the rectum.

Polyps are found and confirmed through colonoscopy, in which a long, thin flexible tube with a camera is passed into the bowel. The NHS says a colonoscopy should not be painful but can feel uncomfortable, and polyps are usually removed during the procedure with a wire loop in a painless step called a polypectomy. The removed tissue is sent to a laboratory to check whether the polyp has been fully removed and whether there are any cancerous changes.

NHS England's genomics education programme states that patients with SPS have an overall lifetime risk of colorectal cancer of between 7% and 70%, and that the risk is increased in first-degree relatives. The range is very wide because the condition is varied. Your own specialist team's assessment matters more than the headline range.

The same source explains that colonoscopic surveillance is highly effective in managing cancer risk and that surgery to remove part of the bowel is rarely indicated. The NHS adds that most polyps never become cancerous and that the few that do usually take many years, which is the reason regular removal works.

Although there is clearly a familial component, the genomics resource says SPS is rarely due to a single-gene condition, with only a very small proportion of cases, about 1 in 300, caused by pathogenic variants in the RNF43 gene. Other polyposis syndromes may present with serrated lesions, so genomic testing can help tell SPS apart from other inherited polyposis conditions.

Under the NHS England test directory, testing is available to a living affected person with a clinical diagnosis if they are younger than 50, have an affected first-degree relative with SPS, or have dysplasia within any polyp. A genetic diagnosis of an RNF43-related form does not change surveillance for the affected person, but it matters for testing relatives. If no variant is found, genetic testing is not recommended for unaffected relatives, although enhanced bowel surveillance may be.

Following the British Society of Gastroenterology guideline as summarised by NHS England's genomics programme, patients with SPS should have colonoscopic surveillance yearly once the colon has been cleared of all lesions greater than 5mm in size. If no polyps of 10mm or more are identified at subsequent examinations, the interval can be extended to once every two years.

People with a confirmed heritable form are referred to the regional genetics service and to a specialist polyposis service. Between colonoscopies the NHS advises seeing a GP if you have mucus or blood in your poo for 3 weeks or more, a change in bowel habit, constipation that is not improving, or noticeable weight loss without trying. Ask for an urgent appointment or call NHS 111 for diarrhoea lasting more than 7 days, black or dark red poo or bloody diarrhoea, and go to A&E or call 999 for non-stop bleeding from the bottom or a lot of blood.

The risk of bowel cancer and polyps is increased in close relatives. NHS England's genomics resource recommends that first-degree relatives are offered a first colonoscopy at the age of 40, or 10 years before the age at diagnosis of the affected person, whichever is earlier. Where a gene variant has been found in the family, relatives may be offered a predictive test, and each child or sibling of a carrier has a 50% chance of having the same variant.

The NHS also notes that you may be more likely to develop bowel polyps if a family member has had polyps or bowel cancer, you are over 50, you have inflammatory bowel disease, or you are overweight or smoke. Reducing the last two is within your control.