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    Genetics of Colorectal Cancer (PDQ®): Genetics - Health Professional Information [NCI] - Major Genetic Syndromes

    Table 10. Clinical Practice Guidelines for Colon Surveillance of BiallelicMYH-Associated Polyposis (MAP) continued...

    The study authors recommend consideration of POLE and POLD1 testing in patients with multiple or large adenomas in whom alternatives mutation testing is uninformative and surveillance akin to that afforded patients with LS or MAP.[209,210]POLE and POLD1 mutation testing is being incorporated into the new multigene CRC susceptibility panels offered commercially.

    A majority of patients with oligopolyposis involving adenomas are currently not found to have an underlying predisposition when evaluated for mutations in known predisposition genes. Such cases are generally managed as if they are at an increased risk of recurrent adenomas even when the colon can be "cleared" of polyps endoscopically.

    Oligopolyposis caused by juvenile polyposis syndrome (JPS) or PJS can readily be distinguished from adenomatous polyposis on simple endoscopic and histologic grounds. Serrated polyposis can present in highly variable fashion. The World Health Organization (WHO) criteria for serrated polyposis (≥5 serrated polyps proximal to sigmoid with 2 ≥1 cm, or any number of polyps proximal to sigmoid if there is a relative with serrated polyposis, or >20 serrated polyps anywhere in the colon) have never been validated. Furthermore, no genetic basis has been established, even in the uncommon familial cases. But cases of oligopolyposis of the serrated variety can initially be challenging to distinguish from oligoadenomatosis, particularly when there is an admixture of adenomas. Consequently, such patients are increasingly being referred for genetic counseling and for consideration of genetic testing. Occasional cases of MYH biallelic mutations have been found in patients with at least some features of serrated polyposis and serrated polyps can be seen in LS. Generally though, the genetic workup of serrated polyposis is unrewarding.[211,212,213,214,215]

    Lynch Syndrome (LS)

    Between 1900 and 1990, numerous case reports of families with apparent increases in CRC were reported. As series of such reports accumulated, certain characteristic clinical features emerged: early age at onset; high risk of second primary tumors; preferential involvement of the right colon; improved clinical outcome; and a range of associated extracolonic sites including the endometrium, ovaries, other sites in the GI tract, uroepithelium, brain, and skin (sebaceous tumors). Terms such as Lynch 1 (families with CRC only), Lynch 2 (families with CRC and extracolonic tumors), cancer family syndrome, and later, hereditary nonpolyposis colorectal cancer (HNPCC), were commonly employed.

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