Investigations

1st investigations to order

genetic testing

Test
Result
Test

Predictive genetic testing for at-risk patients (i.e., patients with a family history of familial adenomatous polyposis [FAP]) and patients with suspected FAP is required for diagnosis.[9][12][24][28][30]

Most cases of FAP are caused by a germline mutation in the tumour-suppressor gene adenomatous polyposis coli, but some cases result from germline mutations in POLD1, POLE, or GREM1.[16][17][18][19]​​ If the pathogenic variant is already known, patients should undergo genetic testing for the identified familial pathogenic variant.[9] Where there are no known pathogenic variants in any polyposis genes, the National Comprehensive Cancer Network (NCCN) recommends germline multigene panel testing.[9] Germline testing is important to differentiate between other aetiologies of adenomatous polyposis (e.g., MUTYH-associated polyposis) for the consideration of extracolonic screening, as well as counselling, risk assessment, and testing of family members.[9] While the identification of a pathogenic variant confirms the diagnosis, FAP should not be excluded even where a pathogenic variant cannot be identified.[24]

Result

germline mutations in APC, POLD1, POLE, or GREM1 genes

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