Tests

1st tests 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 polyposis are caused by a germline mutation in the tumor-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 etiologies of adenomatous polyposis (e.g., MUTYH-associated polyposis) for the consideration of extracolonic screening, as well as counseling, 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]

If there are existing genetic test results, do not order a duplicate test unless there is uncertainty about the existing result, e.g., the result is inconsistent with the patient’s clinical presentation or the test methodology has changed.[31]

Result

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

Use of this content is subject to our disclaimer