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Cancer Health Center

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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...

Mutational testing for germline alterations has been somewhat disappointing, as no more than half of suspected HNPCC cases have detectable pathologic mutations. Because of this, and the lack of sufficiently specific clinical features, various genetic screening strategies have emerged to improve the yield of genetic testing. A sufficiently compelling family history, ideally complemented by the presence of MSI, warrants mutational testing, and most clinical practice guidelines provide for such an approach. The Bethesda guidelines are a combination of clinical, pathologic, and family history features that are sufficiently predictive to warrant MSI/IHC screening. Computer risk-assessment profiles have been developed to do this same work more quantifiably and can estimate mutation risk likelihood with or without the intermediate step of using MSI/IHC.

Against this background of potential clinical selection criteria for mutation testing, population studies have emerged that can estimate HNPCC frequency (1%-3%) and determine the performance characteristics of these same selection tools when implemented in otherwise unselected cases.

The combination of genetic counseling/testing strategies with clinical screening/treatment measures has led to the development of consensus clinical practice guidelines. These guidelines can be used by providers and patients alike to better understand the available options and key decision-points that exist. (Refer to Table 11 for more information about practice guidelines for diagnosis and colon surveillance in LS.)

Terminology related to familial CRC has certainly evolved. Most in the field use the term Lynch syndrome (LS) as a preferred synonym over HNPCC, since HNPCC is both excessively wordy and misleading-many patients have polyps and many have tumors other than CRC. In addition, entities such as Muir-Torre syndrome are now recognized as phenotypic variants of LS. Even Turcot syndrome, which was initially thought to only be an FAP variant, is now known to be an LS variant when it presents with glioblastomas and an FAP variant when it presents with medulloblastomas. It has been suggested that the term LS be applied to cases in which the genetic basis can be confidently linked to a germline mutation in a DNA MMR gene (either a germline mutation is present or can be confidently inferred based on the clinical presentation combined with MSI/IHC).[216]

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