Somatic BRAF-V600E mutations in familial colorectal cancer.

The BRAF gene is mutated in 4% to 12% of unselected colorectal cancers, particularly those with high microsatellite instability and in premalignant lesions, such as serrated adenomas and hyperplastic polyps. However, it has been shown that activating BRAF mutations are almost never found in tumors from hereditary nonpolyposis colorectal cancer patients. To evaluate the role of oncogenic BRAF mutations in non-hereditary nonpolyposis colorectal cancer/non-familial adenomatous polyposis familial colorectal cancer, we did a mutation screening of the most common BRAF mutation, the V600E mutation, in 194 colorectal tumors from patients with a positive family history of the disease. The BRAF-V600E mutation was identified in 100% (8 of 8) of microsatellite-unstable tumors and in 9.7% (18 of 186) of microsatellite-stable tumors. Interestingly, families with extracolonic tumors showed a much higher mutation frequency (17.5%) compared with families with colonic cancer only (3.5%; P = 0.009). In addition, we studied colonoscopic results from 448 family members who had been under colonoscopic surveillance for several years. Subjects from families where the V600E mutation was identified had less adenomas compared with those from families where no BRAF mutation had been found (odds ratio, 8.5; 95% confidence interval, 1.1-64.6). These findings indicate that adenomas might be less important in the cancer development in the group of families with BRAF-V600E mutations and indirectly support a previous hypothesis that tumors might develop through the hyperplastic polyp-serrated adenoma pathway. In conclusion, our results suggest that BRAF-V600E mutations are mainly involved in colorectal cancer families characterized by an increased risk of other common malignancies.     

Current approaches in familial colorectal cancer: a clinical perspective

Individuals with a family history of colorectal cancer or colorectal adenomas have an increased risk for colorectal cancer. When no hereditary syndrome is evident, screening is based on empiric risk estimates. The risk is greatest for individuals with specific inherited cancer-predisposing disorders. When conditions such as familial adenomatous polyposis or hereditary nonpolyposis colorectal cancer are diagnosed, specific neoplasm risk estimates can usually be performed based on advances in molecular genetics. These estimates lead to more straightforward and cost-effective approaches to surveillance and management. The National Comprehensive Cancer Center Network (NCCN) and other groups have provided detailed guidelines for evaluating patients based on recognition of clinical syndrome characteristics, followed by appropriate genetic counseling, genetic testing, and optimal surveillance. The NCCN guidelines are used as a frame of reference for this discussion of selected recent advances in human cancer genetics as they apply to clinical practice.     

Cancer screening guidelines and prevention factors for high-risk patients with a family history of colorectal cancer

Family history of colorectal cancer or of adenomas may confer significant risk of colorectal cancer. Ideally, diagnosis of an inherited syndrome such as familial adenomatous polyposis (FAP) or hereditary nonpolyposis colorectal cancer (HNPCC) enables a molecular biology-driven approach to screening and management. When no hereditary syndrome can be established, clinicians must rely on empiric risk estimates and offer screening accordingly. Detailed rationale and guidelines for use of syndrome characteristics including genetic testing, counseling, and selection of surveillance tools are discussed.     

Microsatellite instability of cancers and concomitant adenomas in synchronous multiple colorectal cancer patients

The precise role of microsatellite instability (MSI) in the development of multiple colorectal cancers has not been elucidated. In the present study, the authors examined MSI and the clinicopathological features of both cancers and concomitant adenomas in nonfamilial multiple synchronous colorectal cancer (multiple CC) patients. Fifty adenomas and 108 cancers were obtained from the surgically resected specimens of 51 multiple CC patients. Nine microsatellite markers were used to determine MSI by polymerase chain reaction (PCR). The frequency of MSI-H adenomas in multiple CC patients was higher than that in single CC patients, while MSI-H frequency of cancers was similar to that in single CC patients. There was a tendency that, in multiple CC patients, when a patient has an MSI-H adenoma, he/she also has MSI-H cancer. The clinicopathological features of multiple CC were similar to those of single CC except the ratio of mucinous cancer and concomitant adenomas. According to this study, in some multiple CC patients, genetic instability seems to play an important role in the development of cancers as well as adenomas. We regard MSI testing for multiple CC patients is useful to distinguish "MSI-related" multiple CC from "MSI-unrelated" multiple CC, and MSI-related multiple CC should be followed up carefully as hereditary nonpolyposis colorectal cancer (HNPCC) patients.     

Microsatellite instability and mismatch-repair protein expression in hereditary and sporadic colorectal carcinogenesis

Aberrant crypt foci (ACF) are microscopic clusters of altered colonic crypts considered premalignant lesions in the large bowel. Genomic instability at short tandem repeats in the DNA, referred to as microsatellite instability (MSI) is the hallmark of hereditary nonpolyposis colorectal carcinoma (HNPCC) caused by mutations in DNA mismatch-repair genes, mostly hMLH1 and hMSH2. In this study, we evaluated for MSI ACF (n = 16), adenomas (n = 18), carcinomas (n =22), and lymph node metastases (n = 3) from 17 patients with colorectal cancer positive for MSI. Ten patients were members of HNPCC families; 7 patients had no family history of cancer. MSI was found in 7 of 7 (100%) ACF and 11 of 12 (91%) adenomas from patients with HNPCC. MSI was not related to histology and size of ACF. A progressive increase in instability as estimated by the number of shifted bands was observed along the ACF-adenoma-carcinoma sequence. In contrast, two of nine (22%) ACF and none of six adenomas from patients with MSI sporadic carcinoma were unstable at microsatellite loci. hMLH1 or hMSH2 protein expression was altered only in MSI-positive premalignant lesions (ACF and/or adenomas), but not in all MSI-positive lesions in patients with HNPCC. These observations provide evidence of the premalignant nature of ACF in HNPCC and suggest that MSI is a very early event both in HNPCC and in sporadic colorectal carcinogenesis, although in the latter it seems infrequent.     

A case of Muir-Torre syndrome associated with mucinous hepatic cholangiocarcinoma and a novel germline mutation of the <Emphasis Type="Italic">MSH2</Emphasis> gene

Muir-Torre syndrome (MTS) is a rare cancer-predisposing syndrome that is autosomal dominantly inherited and characterized by the development of sebaceous skin lesions (adenomas, epitheliomas, basaliomas and carcinomas). These lesions are typically associated with tumors that belong to the spectrum of hereditary nonpolyposis colorectal cancer (HNPCC) (i.e. tumors of the colorectum, endometrium, stomach or ovary). Biliary malignancy in association with MTS has only rarely been reported. We report a case of Muir-Torre syndrome associated with intrahepatic cholangiocarcinoma, a location not previously described, and associated with a novel missense mutation of the MSH2 gene (c.2026T > C), predicted to disrupt the function of the gene.     

Screening and surveillance for colorectal cancer.

Colorectal cancer is the second most common cause of cancer death among American men and woman. Currently available screening and surveillance techniques are effective in detecting early-stage colorectal cancer and its premalignant precursor lesion, the adenomatous polyp (adenoma). Removal of adenomas by colonoscopic polypectomy significantly reduces the incidence of colorectal cancer. Appropriate screening and surveillance recommendations should be based on the individual's colorectal cancer risk stratification. High-risk groups, such as patients with hereditary nonpolyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP), should be offered genetic counseling and specialized screening recommendations for colorectal and associated extracolonic malignancies.     

Hereditary nonpolyposis colorectal cancer associated with duodenal carcinoma: a case report

Hereditary nonpolyposis colorectal cancer is an autosomal, dominantly inherited disease, characterized by an early age of onset, right colon predominance and an association with various extracolorectal malignancies. We present a case of a 47-year-old woman who met the clinical criteria for the diagnosis of hereditary nonpolyposis colorectal cancer from her past and family histories. She had undergone operations for uterine cancer (histology not confirmed) at age 35 and for advanced cancer of the ascending colon at age 45. Gastroendoscopy revealed a flat elevated lesion, 20 mm in size, with a protrusion (type IIa + Is) in the second portion of the duodenum in March 1996. Additionally, colonoscopy showed a flat elevated lesion, 30 mm in size, with an irregular and nodular surface (type IIa, laterally spreading tumor) in the descending colon. After the operation, the resected specimen of the duodenum histologically showed a well-differentiated adenocarcinoma associated with a tubulo-villous adenoma which had invaded the submucosal layer. The tumor of the colon was histologically confirmed to be a moderately-differentiated adenocarcinoma with submucosal invasion. A high frequency of replication error positivity (4/5 loci) was detected in both of the tumors. Reports of early cancer of the duodenum, associated with extracolorectal malignancies in hereditary nonpolyposis colorectal cancer, are very rare in the literature. Although it is difficult to determine which extracolorectal tumor sites should be taken into consideration by screening programs, we believe that careful observation by upper gastrointestinal endoscopy, which includes the duodenum, is necessary for patients with hereditary nonpolyposis colorectal cancer.      

The case for a genetic predisposition to serrated neoplasia in the colorectum: hypothesis and review of the literature.

In recent years, an alternative pathway of colorectal cancer development has been described in which serrated polyps replace the traditional adenoma as the precursor lesion. Importantly, serrated polyps and a subset of colorectal cancer show largely nonoverlapping mutation profiles to those found in adenomas and the majority of colorectal cancer. These genetic alterations include activating mutation of the BRAF proto-oncogene and widespread gene promoter hypermethylation (CpG island methylator phenotype or CIMP). Up to 15% of colorectal cancer is likely to develop on the basis of a strong genetic predisposition. The two most well-characterized syndromes, familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer (Lynch syndrome), both develop via the adenoma-carcinoma pathway and together account for approximately one third of familial colorectal cancer. We have recently described 11 families in which there is evidence that the genetic predisposition to autosomal dominant colorectal cancer is linked to the serrated pathway. This condition, serrated pathway syndrome, and the related condition, hyperplastic polyposis, the presentation of which suggests a recessive mode of inheritance, represent two syndromes in which BRAF mutation and methylation co-occur within serrated precursor lesions. Further, CIMP is observed in the normal colonic mucosa of individuals with hyperplastic polyposis consistent with a field defect in epigenetic regulation. The spectrum of serrated neoplasia may also implicate the apparently sporadic and later onset subset of colorectal cancer with high levels of microsatellite instability. The tendency for these lesions to be multiple, associated with smoking, and to show frequent BRAF mutation and CIMP points to a defect that may result from interactions between the environment and a weakly penetrant genetic alteration.     

Patient and tumor characteristics of colon cancers with microsatellite instability: a population-based study.

Molecular screening for microsatellite instability (MSI) in colon cancers has been proposed to identify individuals with hereditary nonpolyposis colorectal cancer. To date, most reports of MSI in colorectal cancer have been based on studies of clinical case series or high-risk families. We examined the proportion of incident colon cancers in the general population that exhibit MSI by patient and tumor characteristics. We interviewed 201 colon cancer cases ascertained by the New Mexico Tumor Registry in the metropolitan Albuquerque area for demographic information, lifestyle factors, medical history, and family cancer history. Paired normal and tumor tissue specimens were obtained for each case. Three microsatellite markers were used; instability was defined as observed alteration at two or more loci. Overall, 37 of 201 (18%) colon cancers exhibited instability. MSI was more common among cases >70 years (26%) and most common among cases >80 years (38%). MSI was significantly associated with tumors in the proximal colon and with later stage and poor differentiation among cases >70 years. MSI was not associated with a history of polyps. Family history of colorectal cancer was associated with MSI only among cases <50 years. When all factors were analyzed jointly in a regression model, proximal subsite and poor differentiation remained significantly associated with MSI. One patient, whose tumor exhibited MSI, fulfilled the Amsterdam Criteria for hereditary nonpolyposis colorectal cancer. Our study provides a population-based estimate of MSI in colon tumors and a representative estimate of the proportion of colorectal cancer patients in the general population who consent to be interviewed for family cancer history and to have biological samples analyzed.     

Molecular biology in the development of colorectal cancer

In 1988, Vogelstein and colleagues published a paper entitled "Genetic alterations during colorectal-tumor development." This marked the beginning of a series of advances in our understanding of how colorectal cancer develops. This paper also provided evidence for the adenoma-carcinoma sequence. Furthermore, the importance of DNA mismatch repair genes in hereditary nonpolyposis colorectal cancer has been recognized. We herein discuss the development of colorectal cancer on the basis of molecular biology, including specific abnormalities of related genes.     

A homozygous mutation in MSH6 causes Turcot syndrome.

Heterozygous mutations in one of the DNA mismatch repair genes cause hereditary nonpolyposis colorectal cancer (MIM114500). Turcot syndrome (MIM276300) has been described as the association of central nervous system malignant tumors and familial colorectal cancer and has been reported to be both a dominant and recessive disorder. Homozygous and compound heterozygous mutations in APC, MLH1, MSH2, and PMS2 genes have been reported in five families. Here we describe a nonconsanguineous Pakistani family, including a son with lymphoma and colorectal cancer diagnosed at ages 5 and 8, respectively, and an 8-year-old daughter with glioblastoma multiforme. Both children had features of neurofibromatosis type 1 including atypical café au lait spots and axillary freckling without a family history consistent with neurofibromatosis type 1, familial adenomatous polyposis, or hereditary nonpolyposis colorectal cancer. Mutational analysis was done for MLH1, MSH2, and MSH6 using denaturing high-performance liquid chromatography and sequencing of a blood sample from the daughter. A novel homozygous single base insertion mutation was identified (3634insT) resulting in a premature stop at codon 1,223 in exon 7 of the MSH6 gene. Both parents were found to be heterozygous for the 3634insT mutation. Microsatellite instability testing showed instability in the glioblastoma sample. We report here the first identification of a homozygous mutation in MSH6 in a family with childhood-onset brain tumor, lymphoma, colorectal cancer, and neurofibromatosis type 1 phenotype. Our findings support a role for MSH6 in Turcot syndrome and are consistent with an autosomal recessive mode of inheritance.     

Familial pancreatic cancer

Pancreatic cancer is the fourth leading cause of cancer death in both men and women in the United States and will be responsible for an estimated 28,900 deaths in 2001. Relatively little is known of its etiology, and the only well-established risk factor is cigarette smoking. Studies over the past 3 decades have shown that 4%-16% of patients with pancreatic cancer have a family history of the disease. A small fraction of this aggregation can be accounted for in inherited cancer syndromes, including familial atypical multiple-mole melanoma, Peutz-Jeghers syndrome, hereditary breast-ovarian cancer, hereditary pancreatitis, and hereditary nonpolyposis colorectal cancer. These syndromes arise as a result of germline mutations in the BRCA2, pl6 (familial atypical multiple-mole melanoma), mismatch repair (hereditary nonpolyposis colorectal cancer), and STK11 (Peutz-Jeghers syndrome) genes. In addition, hereditary plays a role in predisposing certain patients with apparently sporadic pancreatic cancer. Many patients with pancreatic cancers caused by a germline mutation in a cancer-causing gene do not have a pedigree that is suggestive of a familial cancer syndrome. A recent prospective analysis of the pedigrees in the National Familial Pancreatic Tumor Registry found that individuals with a family history of pancreatic cancer in multiple first-degree relatives have a high risk of pancreatic cancer themselves. The identification of such high-risk individuals will help clinicians target screening programs and develop preventive interventions with the hope of reducing the mortality of pancreatic cancer in these families.     

Levels of colorectal ornithine decarboxylase activity in patients with colon cancer, a family history of nonpolyposis hereditary colorectal cancer, and adenomas.

Ornithine decarboxylase (ODC), a key enzyme in mammalian polyamine biosynthesis, has been proposed to be a marker of colonic epithelial cell proliferation and risk for colorectal cancer. We investigated the basal levels of ODC activity in sigmoid and rectal mucosae, and basal and tumor promoter 12-O-tetradecanoylphorbol-13-acetate-induced levels of skin ODC activity in individuals with a personal history of colon cancer (n = 9 colon; n = 58 skin), a family history of nonpolyposis hereditary colorectal cancer (n = 49; n = 42), adenomas (n = 16; n = 40), and healthy, family history-negative control subjects (n = 40; n = 79). Using a fresh tissue assay and samples obtained after a standard colon lavage preparation, colon mucosal ODC levels ranged from 0 to 192 pmol/mg/h (sigmoid, 0-163 pmol/mg/h; mean, 36 +/- 32 pmol/mg/h; rectum, 0-192 pmol/mg/h; mean, 35 +/- 32 pmol/mg/h). No differences among the four groups of subjects were found for either colon or skin ODC levels, and there were no sex differences overall or in any group. These results are not compatible with the suggestion that ODC levels are a useful marker of risk for colorectal cancer.     

Working through a diagnostic challenge: colonic polyposis,Amsterdam criteria,and a mismatch repair mutation

The two most common causes of hereditary colorectal cancer are Lynch syndrome and familial adenomatous polyposis (FAP). The phenotype of Lynch syndrome, also known as hereditary nonpolyposis colorectal cancer (HNPCC), is differentiated in part from FAP by the lack of profuse colonic polyposis. Here we describe a proband who presented with greater than 50 adenomatous colonic polyps prior to developing cancer of the colon and urinary bladder, and a family history that fulfills the Amsterdam criteria. Germline analyses of APC and MYH in the proband did not reveal any mutations. Comprehensive analysis of the mismatch repair genes associated with Lynch syndrome revealed a germline hMSH6 missense mutation 2314C>T (arg772trp) and normal sequencing for hMSH2 and hMLH1. We outline evidence supporting the pathogenicity of the identified hMSH6 mutation (arg772trp) and suggest possible etiologies for the unexplained colonic adenomatous polyposis.     

Genetics of colorectal cancer

Approximately 6% of colorectal cancers can be attributed to recognizable heritable germline mutations. Familial adenomatous polyposis is an autosomal dominant syndrome classically presenting with hundreds to thousands of adenomatous colorectal polyps that are caused by mutations in the APC gene. Adenomas typically develop in the midteens in these patients, and colorectal cancer is a virtual certainty if this condition is untreated. A low-penetrance susceptibility allele that is common in Jews from Eastern Europe, APC 11307K, confers a two-fold increased risk of colorectal cancer without the full expression of familial adenomatous polyposis. Biallelic mutations in the MYH gene are associated with an attenuated familial adenomatous polyposis phenotype. Lynch syndrome (hereditary nonpolyposis colorectal cancer) is an autosomal dominant disorder characterized by early onset of colorectal cancer with microsatellite instability. Mutations in mismatch repair genes lead to a lifetime colon cancer risk of 85% in these patients; carcinomas of the endometrium, ovary, and other organs also occur with increased frequency. Although adenomas are not characteristic of the hamartomatous polyp syndromes such as juvenile polyposis and Peutz-Jeghers syndrome, individuals with these diseases have a markedly increased risk of colorectal cancer relative to the general population. In this review, we will describe the phenotypes, genotypes, diagnosis, and management of hereditary colon cancer syndromes.     

Hereditary nonpolyposis colorectal cancer: preventive management

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common form of hereditary colorectal cancer. Inherited mutations in the mismatch repair genes associated with this syndrome have an approximate 80% lifetime risk of colorectal cancer. Since there are no premonitory signs of susceptibility to HNPCC, family history is the initial method for identifying those at increased risk. At risk individuals should undergo genetic counseling and testing. Although an algorithmic indication for genetic testing in at risk HNPCC patients is yet to be determined, many advocate initial screening for microsatellite instability (MSI) of the cancer specimen in individuals suspected of carrying HNPCC mutations. Those who test positive for MSI can then undergo further testing for mutations in the associated germline mismatch repair genes. Techniques for detecting these mutations currently include in vitro synthesized-protein assay, single-strand conformational polymorphism, and DNA sequencing. Given the aggressive nature of HNPCC adenomas, individuals who test positive for HNPCC mutations are recommended to undergo yearly colonoscopic surveillance starting at the age of 25. A reasonable alternative to lifetime colonoscopic surveillance for the prevention of colorectal cancer in these individuals is prophylactic colectomy. The prevention of colorectal cancer through pharmacological means is under investigation as another option in the management of HNPCC patients. Specifically, chemoprevention trials are currently ongoing to evaluate the efficacy of COX-2 inhibitors in the prevention of colorectal cancer in HNPCC and familial adenomatous polyposis patients.     

Meat consumption and meat preparation in relation to colorectal adenomas among sporadic and HNPCC family patients in The Netherlands

Meat consumption and meat preparation methods are thought to be associated with the risk of sporadic colorectal cancer, and possibly adenomas. As the same somatic mutations occur in sporadic adenomas and hereditary non-polyposis colorectal cancer (HNPCC)-related adenomas, similar exogenous factors may play a role in the development of both types of adenoma. In a case control study among 57 sporadic colorectal adenoma cases and 62 adenoma cases from HNPCC families (and 148 adenoma-free controls) from the Netherlands, we examined whether meat consumption and preparation are similarly associated with sporadic and suspected HNPCC colorectal adenomas. Frequency of meat consumption was not significantly associated with adenoma risk in our population of sporadic and HNPCC family cases and controls (Odds Ratios (OR) for high versus low consumption were 1.0 and 0.6, respectively). Interestingly, consumption of red meat and specific preparation methods (i.e., "not adding any water" and " closed lid with most meat types") slightly, but non-significantly, increased the risk of adenomas in the sporadic group only (OR, 95% Confidence Interval (CI): 4.1, 0.7-23.0, 2.0, 0.6-6.5 and 2.6, 0.9-7.2, respectively). This is the first study to examine possible differences or similarities in risk factors for sporadic and HNPCC colorectal carcinogenesis. Our results do not provide support for meat consumption as a risk factor for adenoma formation in HNPCC family members. Some characteristics of habitual meat preparation in the Netherlands may, however, increase the risk of sporadic adenomas.