Updates in the field of hereditary nonpolyposis colorectal cancer
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Introduction Up to one third of colorectal cancers show familial clustering and 5% are hereditary single-gene disorders. Hereditary non-polyposis colorectal cancer comprises DNA mismatch repair-deficient and -proficient subsets, represented by Lynch syndrome (LS) and familial colorectal cancer type X (FCCTX), respectively. Accurate knowledge of molecular etiology and genotype-phenotype correlations are critical for tailored cancer prevention and treatment.Areas covered The authors highlight advances in the molecular dissection of hereditary non-polyposis colorectal cancer, based on recent literature retrieved from PubMed. Future possibilities for novel gene discoveries are discussed.Expert commentary LS is molecularly well established, but new information is accumulating of the associated clinical and tumor phenotypes. FCCTX remains poorly defined, but several promising candidate genes have been discovered and share some preferential biological pathways. Multi-level characterization of specimens from large patient cohorts representing multiple populations, combined with proper bioinformatic and functional analyses, will be necessary to resolve the outstanding questions.Keywords:
Lynch Syndrome
Individuals with Lynch syndrome, sometimes referred to as hereditary non-polyposis colorectal cancer (HNPCC), have an increased risk of developing colorectal cancer (CRC) as well as other cancers. The increased risk is due to inherited mutations in mismatch repair (MMR) genes, which reduce the ability of cells to repair DNA damage. Screening for Lynch syndrome in individuals newly diagnosed with colorectal cancer has been proposed as part of a strategy that combines tests and interventions to reduce the risk of colorectal cancer in the relatives of the colorectal cancer patients with Lynch Syndrome.
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Lynch syndrome represents 1-7% of all cases of colorectal cancer and is an autosomal-dominant inherited cancer predisposition syndrome caused by germline mutations in deoxyribonucleic acid (DNA) mismatch repair genes. Since the discovery of the major human genes with DNA mismatch repair function, mutations in five of them have been correlated with susceptibility to Lynch syndrome: mutS homolog 2 (MSH2); mutL homolog 1 (MLH1); mutS homolog 6 (MSH6); postmeiotic segregation increased 2 (PMS2); and postmeiotic segregation increased 1 (PMS1). It has been proposed that one additional mismatch repair gene, mutL homolog 3 (MLH3), also plays a role in Lynch syndrome predisposition, but the clinical significance of mutations in this gene is less clear. According to the InSiGHT database (International Society for Gastrointestinal Hereditary Tumors), approximately 500 different LS-associated mismatch repair gene mutations are known, primarily involving MLH1 (50%) and MSH2 (40%), while others account for 10%. Much progress has been made in understanding the molecular basis of Lynch Syndrome. Molecular characterization will be the most accurate way of defining Lynch syndrome and will provide predictive information of greater accuracy regarding the risks of colon and extracolonic cancer and enable optimal cancer surveillance regimens.
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Lynch syndrome (synonymous for HNPCC = hereditary non-polyposis colorectal cancer) is characterized by the development of colorectal, endometrial, gastric, and various other cancers, and is caused by a mutation in one of the mismatch repair (MMR) genes. One of the main challenges in the clinical management of Lynch syndrome remains the broad spectrum and heterogeneity among and between affected families. To date, no clinically relevant genotype-phenotype correlation for the two main affected genes hMSH2 and hMLH1 has been established. Clinical management of familial colorectal cancer (CRC) remains a challenge for clinicians. The overlap of syndromes with different underlying genetic causes and the differentiated risk management of colorectal and associated malignancies require state-of-the-art management recommendations. Regarding the identification of Lynch syndrome, the available criteria (revised Bethesda guidelines) appear to be effective for the selection of families for analysis of tumor MMR status. To date, the significant proportion of mutation carriers in Germany are still unknown and diagnosis still relies on patients with index cancers. Taking into account the tremendous importance the identification of MMR mutation carriers implies, future directives could include routine antibody staining for MMR genes in all CRCs. Increasing evidence suggests that microsatellite instability (MSI) and/or immunohistochemical (IHC) are an important prognostic factor and may predict the response to chemotherapy, therefore a broad application of these tools is envisaged in the near future.
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The aim of this study was to compare the results of protein level of the DNA mismatch repair genes with the clinical diagnosis of Lynch syndrome according to the Amsterdam II criteria in patients 50 years and younger who underwent surgery for colorectal cancer. The subjects of analysis were 48 patients 50 years old and younger. Immunohistochemistry assays were performed to detect proteins from the DNA mismatch repair genes. Clinicopathological data and Amsterdam II criteria for the diagnosis of hereditary nonpolyposis colorectal cancer were obtained by analyzing medical records. Two (4 %) patients satisfied the Amsterdam II criteria for Lynch syndrome, and both presented levels of all of the studied mismatch repair proteins. A total of 13 (27 %) patients exhibited the absence of protein levels of the studied mismatch repair genes. None of these patients were considered suspicious for Lynch syndrome according to the Amsterdam II criteria. Screening for the level of proteins of the mismatch repair system in all colorectal cancer patients 50 years and younger can increase the identification of patients with suspicion of Lynch syndrome.
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Lynch syndrome (LS) is the most common form of hereditary colorectal cancer (CRC), and previously it was called hereditary non-polyposis colorectal cancer (HNPCC). LS is an inherited tumor predisposing condition caused by mutations in the DNA mismatch repair (MMR) genes (MLH1, MSH2, MSH6 or PMS2) or in the EPCAM gene, which inactivates MSH2 via promoter hypermethylation. The proteins produced by MLH1, MSH2, MSH6 and PMS2 form heterodimeric complexes, which play an essential role in DNA repair. Genotype–phenotype correlations are established because cancer risk depends on the mutated MMR gene. The genotype deficient in MMR genes (MMR deficient) is associated with a lifetime cancer risk of 58–75% with frequent observations of the development of synchronous/metachronous tumors. Lynch-associated CRCs behave differently than sporadic CRCs, which has significant implications for clinical management. Histopathological examination of Lynch-associated CRCs often reveals abundant lymphocytes infiltrating the tumor.
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Heterozygous carriers of a pathogenic variant in the mismatch repair genes have an increased risk to develop colorectal cancer and various other types of cancer during adulthood. This cancer predisposition syndrome is called Lynch syndrome. Children who carry a mutation on both copies of a mismatch repair gene develop malignancies during childhood or adolescence. This syndrome is called constitutional mismatch repair deficiency (CMMRD). The aim of this thesis is 1) to provide insights that may help in the identification of patients with Lynch syndrome and CMMRD, and 2) to further elucidate the phenotype and potential modifying factors that result from carrying a germline pathogenic variant in one of the mismatch repair genes. Both aims are important to further facilitate adequate detection and surveillance.
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