Insights into familial colon cancer: The plot thickens

Abstract

Evidence indicates that colorectal cancer (CRC) risk is conferred by both genetic and environmental factors. A well-described sequence of molecular genetic changes accompany the development and progression of precursor lesions to invasive malignancy.1Chung D.C. Rustgi A.K. DNA mismatch repair and cancer.Gastroenterology. 1995; 109: 1685-1689Abstract Full Text PDF PubMed Scopus (140) Google Scholar Two major pathways of tumorigenesis have been described and include the chromosomal instability (CIN) pathway that is associated with frequent chromosomal allelic loss and aneuploidy.2Fearon E.R. Volgelstein B. A genetic model for colorectal tumorigenesis.Cell. 1990; 61: 759-767Abstract Full Text PDF PubMed Scopus (9879) Google Scholar The other pathway is characterized by microsatellite instability (MIN; referred to here as MSI). MSI results in numerous mutations that occur in microsatellite sequences consisting of mono- and dinucleotide repeats scattered throughout the genome.3Ionov Y. Peinado M.A. Malkhosyan S. et al.Ubiquitous somatic mutations in simple repeated sequences reveal a new mechanism for colonic carcinogenesis.Nature. 1993; 363: 558-561Crossref PubMed Scopus (2387) Google Scholar The promoter regions of the following genes frequently are mutated and include proapoptotic BAX, transforming growth factor β type II receptor, and insulin growth factor receptor type II.3Ionov Y. Peinado M.A. Malkhosyan S. et al.Ubiquitous somatic mutations in simple repeated sequences reveal a new mechanism for colonic carcinogenesis.Nature. 1993; 363: 558-561Crossref PubMed Scopus (2387) Google Scholar Sporadic colon cancers with MSI show right-sided colon predominance, as do tumors arising in the syndrome of hereditary nonpolyposis colorectal cancer (HNPCC).4Thibodeau S.N. Bren G. Schaid D. Microsatellite instability in cancer of the proximal colon.Science. 1993; 260: 816-819Crossref PubMed Scopus (2781) Google Scholar MSI is the hallmark of the syndrome of HNPCC, where it occurs as a consequence of a germline mutation in 1 of 4 DNA mismatch repair genes (hMLH1, hMSH2, hMSH6, and PMS2), with the great majority of mutations occurring in hMLH1 and hMSH2 genes.5Marra G. Boland C.R. Hereditary nonpolyposis colorectal cancer the syndrome, the genes, and historical perspectives.J Natl Cancer Inst. 1995; 87: 1114-1125Crossref PubMed Scopus (478) Google Scholar HNPCC accounts for 3%–6% of all CRC cases and familial adenomatous polyposis (FAP), owing to germline mutation in APC, accounts for 1% of incident CRCs.5Marra G. Boland C.R. Hereditary nonpolyposis colorectal cancer the syndrome, the genes, and historical perspectives.J Natl Cancer Inst. 1995; 87: 1114-1125Crossref PubMed Scopus (478) Google Scholar Despite these well-known syndromes, the mechanism(s) underlying the much larger group of suspected familial colon cancer not associated with FAP or HNPCC remains unexplained.Importantly, MSI has also been detected in approximately 15%–20% of sporadic human CRCs, where it is caused by promoter hypermethylation of the hMLH1 gene.6Cunningham J.M. Christensen E.R. Tester D.J. et al.Hypermethylation of the hMLH1 promoter in colon cancer with microsatellite instability.Cancer Res. 1998; 58: 3455-3460PubMed Google Scholar This is an epigenetic event that results in gene silencing and is believed to be nonheritable. These sporadic tumors displaying MSI share certain clinicopathologic features in common with HNPCCs that include proximal colon predominance, poor differentiation, and diploid DNA content.4Thibodeau S.N. Bren G. Schaid D. Microsatellite instability in cancer of the proximal colon.Science. 1993; 260: 816-819Crossref PubMed Scopus (2781) Google Scholar Unlike HNPCC, however, they do not show an early age of onset and are not associated with synchronous tumors or extracolonic malignancies. Retrospective studies suggest that colon cancers with MSI have better stage-adjusted survival rates relative to MSI stable tumors.7Gryfe R. Kim H. Hsieh E.T.K. et al.Tumor microsatellite instability and clinical outcome in young patients with colorectal cancer.N Engl J Med. 2000; 342: 69-77Crossref PubMed Scopus (1161) Google Scholar In addition, a CpG island methylator phenotype (ie, CIMP) is a recently described mechanism for tumorigenesis in colorectal carcinomas and adenomas characterized by methylation of multiple genes rich in CpG islands. CIMP frequently includes the promoter region of the hMLH1 gene and evidence indicates that a significant proportion of sporadic MSI-H colon cancers have CIMP.8Toyota M. Ahuja N. Ohe-Toyota M. et al.CpG island methylator phenotype in colorectal cancer.Proc Natl Acad Sci U S A. 1999; 96: 8681-8686Crossref PubMed Scopus (2098) Google Scholar At present, the causes of CIMP are unknown. More recently, an oncogenic mutational hotspot within the BRAF gene has been found in sporadic colon cancers with MSI.9Rajagopalan H. Bardelli A. Lengauer C. et al.RAF/RAS oncogenes and mismatch-repair status.Nature. 2002; 418: 934Crossref PubMed Scopus (1050) Google Scholar, 10Davies H. Bignell G.R. Cox C. et al.Mutations of the BRAF gene in human cancer.Nature. 2002; 417: 949-954Crossref PubMed Scopus (8142) Google Scholar BRAF is a kinase-encoding gene from the Ras/Raf/MAPK (mitogen-activated protein kinase) pathway that is activated upon mutation. Data indicate, however, that few, if any, HNPCC cancers show BRAF mutations, suggesting that this event may be useful in distinguishing HNPCC from sporadic colon cancers with MSI.11Domingo E. Laiho P Ollikainen M. et al.BRAF screening as a low-cost effective strategy for simplifying HNPCC genetic testing.J Med Genet. 2004; 41: 664-668Crossref PubMed Scopus (291) Google ScholarIn this month’s issue of Clinical Gastroenterology and Hepatology, Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar report the clinical and pathologic features of a proposed new familial CRC syndrome characterized by colonic tumors with variable levels of MSI (defined as any family in which 2 or more CRCs were discordant for MSI), a high rate of BRAF mutations, and the presence of methylation of the MINT31 (methylated in tumor) CpG island. Cases were obtained from the Queensland, Australia, large-bowel family registry for non-FAP kindreds. Families chosen for study had variable levels of MSI evaluated using a panel of 10 microsatellite markers with categorization as high frequency (MSI-H), low frequency (MSI-L), and microsatellite stable (MSS).13Boland C.R. Thibodeau S.N. Hamilton S.R. et al.A National Cancer Institute workshop on microsatellite instability for cancer detection and familial predisposition development of international criteria for the determination of microsatellite instability in colorectal cancer.Cancer Res. 1998; 58: 5248-5257PubMed Google Scholar All patients with MSI met revised Bethesda guidelines14Umar A. Boland C.R. Terdiman J.P. et al.Revised Bethesda Guidelines for hereditary nonpolyposis colorectal cancer (Lynch syndrome) and microsatellite instability.J Natl Cancer Inst. 2004; 96: 261-268Crossref PubMed Scopus (2420) Google Scholar and 55% fulfilled the Amsterdam I criteria.15Vasen H.F.A. Watson P. Mecklin J.-P. et al.New clinical criteria for hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) proposed by the international collaborative group on HNPCC.Gastroenterology. 1999; 116: 1453-1456Abstract Full Text Full Text PDF PubMed Scopus (2048) Google Scholar Tumors analyzed in this study included polyps and cancers from 43 subjects belonging to 11 families. Colorectal tumors were subjected to MSI testing and DNA mismatch repair protein expression (analyzed by immunohistochemistry); germline testing for mutations in DNA mismatch repair genes was not performed. CRC cases showed an early age of onset and methylation of the MINT31 CpG island, a gene found to be hypermethylated frequently in colon cancers with CIMP,8Toyota M. Ahuja N. Ohe-Toyota M. et al.CpG island methylator phenotype in colorectal cancer.Proc Natl Acad Sci U S A. 1999; 96: 8681-8686Crossref PubMed Scopus (2098) Google Scholar in 8 of 10 tumors. Promoter methylation of the hMLH1 gene was not evaluated specifically in this study. A mutational hotspot in the BRAF gene, determined using an allele-specific polymerase chain reaction-based assay, was found in 63% of polyps and 70% of cancers, whereas none were found in HNPCC cases, and a frequency of 15% was detected in unselected CRCs. In a larger series of colon cancers reported by Domingo et al,11Domingo E. Laiho P Ollikainen M. et al.BRAF screening as a low-cost effective strategy for simplifying HNPCC genetic testing.J Med Genet. 2004; 41: 664-668Crossref PubMed Scopus (291) Google Scholar a lower frequency of BRAF hotspot mutations was found in that 40% (82 of 206) of MSI-H sporadic colon cancers showed mutations, whereas all 111 HNPCC cases lacked such events. Overall, Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar found the presence of the BRAF mutation in a high proportion of cases and MINT31 hypermethylation in 80% of cancers, which represents strong evidence against HNPCC in the study population. The finding of frequent MINT31 methylation is consistent with CIMP-positive colon cancers as described by Toyota et al.8Toyota M. Ahuja N. Ohe-Toyota M. et al.CpG island methylator phenotype in colorectal cancer.Proc Natl Acad Sci U S A. 1999; 96: 8681-8686Crossref PubMed Scopus (2098) Google Scholar Interestingly, Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar found that 40% of tumors examined in their study showed a serrated architecture, suggesting a link to the serrated adenoma pathway of CRC.16Jass J.R. Serrated adenoma of the colorectum a lesion with teeth.Am J Pathol. 2003; 162: 705-708Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar Serrated adenomas are characterized by a saw-toothed growth pattern with epithelial dysplasia. Evidence suggests that hyperplastic polyps in the right colon and serrated adenomas may be precursors to sporadic colon carcinomas with MSI and in CIMP-positive cases.17Park S.J. Rashid A. Lee J.H. et al.Frequent CpG island methylation in serrated adenomas of the colorectum.Am J Pathol. 2003; 162: 815-822Abstract Full Text Full Text PDF PubMed Scopus (205) Google Scholar, 18Hawkins N.J. Ward R.L. Sporadic colorectal cancers with microsatellite instability and their possible origin in hyperplastic polyps and serrated adenomas.J Natl Cancer Inst. 2001; 93: 1282-1283Crossref PubMed Scopus (305) Google Scholar The data of Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar further support the relationship of MSI, CIMP, and serrated polyps in non-HNPCC patients. Furthermore, these data support the argument that the serrated pathway is a precursor of colon cancers with DNA hypermethylation.At the moment, the provocative findings in the study by Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar may best be described as a potential familial variant of the CIMP pathway. Confirmation of results reported by Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar in a larger study is eagerly awaited. Although their data suggest that the affected families may indeed have CIMP, examination of other genes rich in CpG islands for promoter methylation including hMLH1 will establish CIMP more fully in such cases. The data of Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar add to the growing body of evidence showing that detection of a BRAF mutational hotspot is associated strongly with MSI and CIMP and argues against HNPCC. Specifically, the presence of the BRAF mutational hotspot makes a diagnosis of HNPCC unlikely. Accordingly, mutational analysis of the BRAF hotspot has been advocated as a useful test in the evaluation of patients with suspected HNPCC and may simplify genetic testing.The data of Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar and other recent data19Frazier M.L. Xi L. Zong J. et al.Association of the CpG island methylator phenotype with family history of cancer in patients with colorectal cancer.Cancer Res. 2003; 63: 4805-4808PubMed Google Scholar, 20Ricciardiello L. Goel A. Mantovani V. et al.Frequent loss of hMLH1 by promoter hypermethylation leads to microsatellite instability in adenomatous polyps of patients with a single first-degree member affected by colon cancer.Cancer Res. 2003; 63: 787-792PubMed Google Scholar demonstrate a familial clustering of colon cancers with DNA methylation or CIMP, and frequent BRAF mutations and a potential origin in the serrated hyperplastic polyp/adenoma pathway. The most critical piece of this interesting puzzle is certainly the identification of the gene(s) responsible for this apparent syndrome that can link genetic and epigenetic events during colorectal tumorigenesis. Taken together, the findings of Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar suggest that an expansion of our existing knowledge of familial non-HNPCC colon cancer is on the horizon. Efforts to fill in the missing pieces of the familial colon cancer puzzle are reaping rewards and, clearly, the best is yet to come. Evidence indicates that colorectal cancer (CRC) risk is conferred by both genetic and environmental factors. A well-described sequence of molecular genetic changes accompany the development and progression of precursor lesions to invasive malignancy.1Chung D.C. Rustgi A.K. DNA mismatch repair and cancer.Gastroenterology. 1995; 109: 1685-1689Abstract Full Text PDF PubMed Scopus (140) Google Scholar Two major pathways of tumorigenesis have been described and include the chromosomal instability (CIN) pathway that is associated with frequent chromosomal allelic loss and aneuploidy.2Fearon E.R. Volgelstein B. A genetic model for colorectal tumorigenesis.Cell. 1990; 61: 759-767Abstract Full Text PDF PubMed Scopus (9879) Google Scholar The other pathway is characterized by microsatellite instability (MIN; referred to here as MSI). MSI results in numerous mutations that occur in microsatellite sequences consisting of mono- and dinucleotide repeats scattered throughout the genome.3Ionov Y. Peinado M.A. Malkhosyan S. et al.Ubiquitous somatic mutations in simple repeated sequences reveal a new mechanism for colonic carcinogenesis.Nature. 1993; 363: 558-561Crossref PubMed Scopus (2387) Google Scholar The promoter regions of the following genes frequently are mutated and include proapoptotic BAX, transforming growth factor β type II receptor, and insulin growth factor receptor type II.3Ionov Y. Peinado M.A. Malkhosyan S. et al.Ubiquitous somatic mutations in simple repeated sequences reveal a new mechanism for colonic carcinogenesis.Nature. 1993; 363: 558-561Crossref PubMed Scopus (2387) Google Scholar Sporadic colon cancers with MSI show right-sided colon predominance, as do tumors arising in the syndrome of hereditary nonpolyposis colorectal cancer (HNPCC).4Thibodeau S.N. Bren G. Schaid D. Microsatellite instability in cancer of the proximal colon.Science. 1993; 260: 816-819Crossref PubMed Scopus (2781) Google Scholar MSI is the hallmark of the syndrome of HNPCC, where it occurs as a consequence of a germline mutation in 1 of 4 DNA mismatch repair genes (hMLH1, hMSH2, hMSH6, and PMS2), with the great majority of mutations occurring in hMLH1 and hMSH2 genes.5Marra G. Boland C.R. Hereditary nonpolyposis colorectal cancer the syndrome, the genes, and historical perspectives.J Natl Cancer Inst. 1995; 87: 1114-1125Crossref PubMed Scopus (478) Google Scholar HNPCC accounts for 3%–6% of all CRC cases and familial adenomatous polyposis (FAP), owing to germline mutation in APC, accounts for 1% of incident CRCs.5Marra G. Boland C.R. Hereditary nonpolyposis colorectal cancer the syndrome, the genes, and historical perspectives.J Natl Cancer Inst. 1995; 87: 1114-1125Crossref PubMed Scopus (478) Google Scholar Despite these well-known syndromes, the mechanism(s) underlying the much larger group of suspected familial colon cancer not associated with FAP or HNPCC remains unexplained. Importantly, MSI has also been detected in approximately 15%–20% of sporadic human CRCs, where it is caused by promoter hypermethylation of the hMLH1 gene.6Cunningham J.M. Christensen E.R. Tester D.J. et al.Hypermethylation of the hMLH1 promoter in colon cancer with microsatellite instability.Cancer Res. 1998; 58: 3455-3460PubMed Google Scholar This is an epigenetic event that results in gene silencing and is believed to be nonheritable. These sporadic tumors displaying MSI share certain clinicopathologic features in common with HNPCCs that include proximal colon predominance, poor differentiation, and diploid DNA content.4Thibodeau S.N. Bren G. Schaid D. Microsatellite instability in cancer of the proximal colon.Science. 1993; 260: 816-819Crossref PubMed Scopus (2781) Google Scholar Unlike HNPCC, however, they do not show an early age of onset and are not associated with synchronous tumors or extracolonic malignancies. Retrospective studies suggest that colon cancers with MSI have better stage-adjusted survival rates relative to MSI stable tumors.7Gryfe R. Kim H. Hsieh E.T.K. et al.Tumor microsatellite instability and clinical outcome in young patients with colorectal cancer.N Engl J Med. 2000; 342: 69-77Crossref PubMed Scopus (1161) Google Scholar In addition, a CpG island methylator phenotype (ie, CIMP) is a recently described mechanism for tumorigenesis in colorectal carcinomas and adenomas characterized by methylation of multiple genes rich in CpG islands. CIMP frequently includes the promoter region of the hMLH1 gene and evidence indicates that a significant proportion of sporadic MSI-H colon cancers have CIMP.8Toyota M. Ahuja N. Ohe-Toyota M. et al.CpG island methylator phenotype in colorectal cancer.Proc Natl Acad Sci U S A. 1999; 96: 8681-8686Crossref PubMed Scopus (2098) Google Scholar At present, the causes of CIMP are unknown. More recently, an oncogenic mutational hotspot within the BRAF gene has been found in sporadic colon cancers with MSI.9Rajagopalan H. Bardelli A. Lengauer C. et al.RAF/RAS oncogenes and mismatch-repair status.Nature. 2002; 418: 934Crossref PubMed Scopus (1050) Google Scholar, 10Davies H. Bignell G.R. Cox C. et al.Mutations of the BRAF gene in human cancer.Nature. 2002; 417: 949-954Crossref PubMed Scopus (8142) Google Scholar BRAF is a kinase-encoding gene from the Ras/Raf/MAPK (mitogen-activated protein kinase) pathway that is activated upon mutation. Data indicate, however, that few, if any, HNPCC cancers show BRAF mutations, suggesting that this event may be useful in distinguishing HNPCC from sporadic colon cancers with MSI.11Domingo E. Laiho P Ollikainen M. et al.BRAF screening as a low-cost effective strategy for simplifying HNPCC genetic testing.J Med Genet. 2004; 41: 664-668Crossref PubMed Scopus (291) Google Scholar In this month’s issue of Clinical Gastroenterology and Hepatology, Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar report the clinical and pathologic features of a proposed new familial CRC syndrome characterized by colonic tumors with variable levels of MSI (defined as any family in which 2 or more CRCs were discordant for MSI), a high rate of BRAF mutations, and the presence of methylation of the MINT31 (methylated in tumor) CpG island. Cases were obtained from the Queensland, Australia, large-bowel family registry for non-FAP kindreds. Families chosen for study had variable levels of MSI evaluated using a panel of 10 microsatellite markers with categorization as high frequency (MSI-H), low frequency (MSI-L), and microsatellite stable (MSS).13Boland C.R. Thibodeau S.N. Hamilton S.R. et al.A National Cancer Institute workshop on microsatellite instability for cancer detection and familial predisposition development of international criteria for the determination of microsatellite instability in colorectal cancer.Cancer Res. 1998; 58: 5248-5257PubMed Google Scholar All patients with MSI met revised Bethesda guidelines14Umar A. Boland C.R. Terdiman J.P. et al.Revised Bethesda Guidelines for hereditary nonpolyposis colorectal cancer (Lynch syndrome) and microsatellite instability.J Natl Cancer Inst. 2004; 96: 261-268Crossref PubMed Scopus (2420) Google Scholar and 55% fulfilled the Amsterdam I criteria.15Vasen H.F.A. Watson P. Mecklin J.-P. et al.New clinical criteria for hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) proposed by the international collaborative group on HNPCC.Gastroenterology. 1999; 116: 1453-1456Abstract Full Text Full Text PDF PubMed Scopus (2048) Google Scholar Tumors analyzed in this study included polyps and cancers from 43 subjects belonging to 11 families. Colorectal tumors were subjected to MSI testing and DNA mismatch repair protein expression (analyzed by immunohistochemistry); germline testing for mutations in DNA mismatch repair genes was not performed. CRC cases showed an early age of onset and methylation of the MINT31 CpG island, a gene found to be hypermethylated frequently in colon cancers with CIMP,8Toyota M. Ahuja N. Ohe-Toyota M. et al.CpG island methylator phenotype in colorectal cancer.Proc Natl Acad Sci U S A. 1999; 96: 8681-8686Crossref PubMed Scopus (2098) Google Scholar in 8 of 10 tumors. Promoter methylation of the hMLH1 gene was not evaluated specifically in this study. A mutational hotspot in the BRAF gene, determined using an allele-specific polymerase chain reaction-based assay, was found in 63% of polyps and 70% of cancers, whereas none were found in HNPCC cases, and a frequency of 15% was detected in unselected CRCs. In a larger series of colon cancers reported by Domingo et al,11Domingo E. Laiho P Ollikainen M. et al.BRAF screening as a low-cost effective strategy for simplifying HNPCC genetic testing.J Med Genet. 2004; 41: 664-668Crossref PubMed Scopus (291) Google Scholar a lower frequency of BRAF hotspot mutations was found in that 40% (82 of 206) of MSI-H sporadic colon cancers showed mutations, whereas all 111 HNPCC cases lacked such events. Overall, Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar found the presence of the BRAF mutation in a high proportion of cases and MINT31 hypermethylation in 80% of cancers, which represents strong evidence against HNPCC in the study population. The finding of frequent MINT31 methylation is consistent with CIMP-positive colon cancers as described by Toyota et al.8Toyota M. Ahuja N. Ohe-Toyota M. et al.CpG island methylator phenotype in colorectal cancer.Proc Natl Acad Sci U S A. 1999; 96: 8681-8686Crossref PubMed Scopus (2098) Google Scholar Interestingly, Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar found that 40% of tumors examined in their study showed a serrated architecture, suggesting a link to the serrated adenoma pathway of CRC.16Jass J.R. Serrated adenoma of the colorectum a lesion with teeth.Am J Pathol. 2003; 162: 705-708Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar Serrated adenomas are characterized by a saw-toothed growth pattern with epithelial dysplasia. Evidence suggests that hyperplastic polyps in the right colon and serrated adenomas may be precursors to sporadic colon carcinomas with MSI and in CIMP-positive cases.17Park S.J. Rashid A. Lee J.H. et al.Frequent CpG island methylation in serrated adenomas of the colorectum.Am J Pathol. 2003; 162: 815-822Abstract Full Text Full Text PDF PubMed Scopus (205) Google Scholar, 18Hawkins N.J. Ward R.L. Sporadic colorectal cancers with microsatellite instability and their possible origin in hyperplastic polyps and serrated adenomas.J Natl Cancer Inst. 2001; 93: 1282-1283Crossref PubMed Scopus (305) Google Scholar The data of Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar further support the relationship of MSI, CIMP, and serrated polyps in non-HNPCC patients. Furthermore, these data support the argument that the serrated pathway is a precursor of colon cancers with DNA hypermethylation. At the moment, the provocative findings in the study by Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar may best be described as a potential familial variant of the CIMP pathway. Confirmation of results reported by Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar in a larger study is eagerly awaited. Although their data suggest that the affected families may indeed have CIMP, examination of other genes rich in CpG islands for promoter methylation including hMLH1 will establish CIMP more fully in such cases. The data of Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar add to the growing body of evidence showing that detection of a BRAF mutational hotspot is associated strongly with MSI and CIMP and argues against HNPCC. Specifically, the presence of the BRAF mutational hotspot makes a diagnosis of HNPCC unlikely. Accordingly, mutational analysis of the BRAF hotspot has been advocated as a useful test in the evaluation of patients with suspected HNPCC and may simplify genetic testing. The data of Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar and other recent data19Frazier M.L. Xi L. Zong J. et al.Association of the CpG island methylator phenotype with family history of cancer in patients with colorectal cancer.Cancer Res. 2003; 63: 4805-4808PubMed Google Scholar, 20Ricciardiello L. Goel A. Mantovani V. et al.Frequent loss of hMLH1 by promoter hypermethylation leads to microsatellite instability in adenomatous polyps of patients with a single first-degree member affected by colon cancer.Cancer Res. 2003; 63: 787-792PubMed Google Scholar demonstrate a familial clustering of colon cancers with DNA methylation or CIMP, and frequent BRAF mutations and a potential origin in the serrated hyperplastic polyp/adenoma pathway. The most critical piece of this interesting puzzle is certainly the identification of the gene(s) responsible for this apparent syndrome that can link genetic and epigenetic events during colorectal tumorigenesis. Taken together, the findings of Young et al12Young J. Barker M.A. Simms L.A. et al.Evidence for BRAF mutation and variable levels of microsatellite instability in a syndrome of familial colorectal cancer.Clin Gastroenterol Hepatol. 2005; 3: 254-263Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar suggest that an expansion of our existing knowledge of familial non-HNPCC colon cancer is on the horizon. Efforts to fill in the missing pieces of the familial colon cancer puzzle are reaping rewards and, clearly, the best is yet to come.