Double heterozygosity for BRCA1 and hMLH1 gene mutations in a 46-year-old woman with five primary tumors.

Germline mutations in BRCA1 and BRCA2 genes predispose to hereditary breast cancer, whereas carriers of mutations in any of the mismatch repair genes (MMR; hMLH1, hMSH2, hMSH6, hPMS2) are highly susceptible to Lynch syndrome. In the present study, we describe a woman affected by unilateral breast cancer at the age of 35 years. After 4 years, during the follow-up she developed synchronous (and asymptomatic) endometrial cancer, ovarian carcinoma and renal clear cell carcinoma. After 7 years (at age 46), the patient developed an infiltrating carcinoma of the contralateral breast and died in a few months of metastatic disease. Initial investigations led to the detection of a constitutional mutation in the BRCA1 gene. The extended genealogical tree disclosed a suspected history of colorectal carcinoma in the maternal branch. Endometrial cancer of the proband was investigated for microsatellite instability (MSI) and immunohistochemical expression of MLH1, MSH2 and MSH6 proteins. An high MSI status and lack of expression of MLH1 protein were detected. hMLH1 gene sequencing revealed the presence of a constitutional mutation, which was also found in the mother of the proband. Loss of the wild-type hMLH1 allele was detected in both breast tumors, thus suggesting that the MMR defect contributed to the development of the breast cancer.

Peutz-Jeghers syndrome: a systematic review and recommendations for management.

Peutz-Jeghers syndrome (PJS, MIM175200) is an autosomal dominant condition defined by the development of characteristic polyps throughout the gastrointestinal tract and mucocutaneous pigmentation. The majority of patients that meet the clinical diagnostic criteria have a causative mutation in the STK11 gene, which is located at 19p13.3. The cancer risks in this condition are substantial, particularly for breast and gastrointestinal cancer, although ascertainment and publication bias may have led to overestimates in some publications. Current surveillance protocols are controversial and not evidence-based, due to the relative rarity of the condition. Initially, endoscopies are more likely to be done to detect polyps that may be a risk for future intussusception or obstruction rather than cancers, but surveillance for the various cancers for which these patients are susceptible is an important part of their later management. This review assesses the current literature on the clinical features and management of the condition, genotype-phenotype studies, and suggested guidelines for surveillance and management of individuals with PJS. The proposed guidelines contained in this article have been produced as a consensus statement on behalf of a group of European experts who met in Mallorca in 2007 and who have produced guidelines on the clinical management of Lynch syndrome and familial adenomatous polyposis.

Recommendations to improve identification of hereditary and familial colorectal cancer in Europe.

Familial colorectal cancer (CRC) accounts for 10-15% of all CRCs. In about 5% of all cases, CRC is associated with a highly penetrant dominant inherited syndrome. The most common inherited form of non-polyposis CRC is the Lynch syndrome which is responsible for about 2-4% of all cases. Surveillance of individuals at high risk for CRC prevents the development of advanced CRC. About 1 million individuals in Western Europe are at risk for Lynch syndrome. We performed a survey to evaluate the strategies currently used to identify individuals at high risk for CRC in 14 Western European countries. Questionnaires were distributed amongst members of a European collaborative group of experts that aims to improve the prognosis of families with hereditary CRC. The survey showed that in all countries obtaining a family history followed by referral to clinical genetics centres of suspected cases was the main strategy to identify familial and hereditary CRC. In five out of seven countries with a (regional or national) CRC population screening program, attention was paid in the program to the detection of familial CRC. In only one country were special campaigns organized to increase the awareness of familial CRC among the general population. In almost all countries, the family history is assessed when a patient visits a general practitioner or hospital. However, the quality of family history taking was felt to be rather poor. Microsatellite instability testing (MSI) or immunohistochemical analysis (IHC) of CRC are usually recommended as tools to select high-risk patients for genetic testing and are performed in most countries in patients suspected of Lynch syndrome. In one country, IHC was recommended in all new cases of CRC. In most countries there are no specific programs on cancer genetics in the teaching curriculum for medical doctors. In conclusion, the outcome of this survey and the discussions within an European expert group may be used to improve the strategies to identify individuals at high risk of CRC. More attention should be given to increasing the awareness of the general population of hereditary CRC. Immunohistochemical analysis or MSI-analysis of all CRCs may be an effective tool for identifying all Lynch syndrome families. The cost-effectiveness of this approach should be further evaluated. All countries with a CRC population screening program should obtain a full family history as part of patient assessment.

Differentiated thyroid carcinoma (DTC) in a young woman with Peutz-Jeghers syndrome: are these two conditions associated?

AIMS: Peutz-Jeghers Syndrome (PJS) is a rare dominantly inherited disease characterized by hamartomatous small bowel polyposis, mucocutaneous hyperpigmentation, and increased risk of cancer. Differentiated thyroid cancers (DTCs) present mainly as sporadic, but they may have also a familial component. We present a case of PJS in a caucasian 25 years-old woman, who developed a DTC. METHODS: The patient had a palpable nodule in the right side of the thyroid region and an endocrinological evaluation, including hormonal assays, neck ultrasound (US) and fine needle aspiration (FNAB) of the nodule was performed. RESULTS: US confirmed a single nodular lesion in the right thyroid lobe (14 mm). Cytological analysis at FNAB revealed a pattern compatible with papillary thyroid carcinoma. The histological analysis after total thyroidectomy confirmed the diagnosis of a Hurtle cell variant of papillary thyroid carcinoma, with follicular architecture. CONCLUSION: Even though rare, the association between PJS and DTC can be possible. In clinical practice it must be borne in mind that the wide spectrum of possible cancer diseases occurring in PJS could also include DTC, that the latter can occur earlier in life in PJS population and with a more aggressive histological pattern. Furthermore, in patients with PJS, US of the thyroid should be performed whenever thyroid disease is suspected at physical examination or based on patient's medical history. Due to lack of established data allowing for a real esteem of the association between PJS and DTC, US of the thyroid, should not be recommended as a routine screening for all subjects with PJS.

Epidemiology of colorectal cancer: the 21-year experience of a specialised registry.

UNLABELLED: Cancer registries can be viewed as one of the main strategies for improving our understanding of cancer, as they may reveal the importance of specific trends in cancer incidence and survival; in addition, the information obtained from the registries can be translated into preventive measures that might lead to a better control of neoplasms. A colorectal cancer registry was instituted in Northern Italy in 1984. The purpose of this study is to provide a description of the main findings observed in a 21-year period of continuous registration. RESULTS: A total of 3951 malignancies of the large bowel were registered in 3817 patients, for a crude incidence rate of 75.1/100 000/year in men and 59.0 in women. Overall incidence (crude and age-adjusted) of colorectal tumours increased remarkably throughout the registration period. This increase was mainly due to early (Stage I and II) tumours and to lesions with lymph nodal involvement (Stage III). There was a tendency over time towards a progressive increase of colonic tumours, whereas the fraction of rectal neoplasms tended to decline. Colorectal cancer-specific survival increased significantly over time in each of the main TNM/Dukes classes (p<0.006 and <0.001 for Stage II and III tumours). Finally, surgery for colorectal tumours showed a tendency towards large operations (colectomy and hemicolectomy), which was parallel to a definite improvement of pathological staging. CONCLUSIONS: Despite the increasing incidence of colorectal cancer, there are several reasons for cautious optimism. Most of the lesions are now diagnosed at an early stage, and this is associated with a significant increase of survival. The disease is undoubtedly cured better than in the past; the main challenge for future years is to achieve a sustained reduction of mortality for colorectal neoplasms.

Frequency of constitutional MSH6 mutations in a consecutive series of families with clinical suspicion of HNPCC.

A large majority of constitutional mutations in hereditary non-polyposis colorectal cancer (HNPCC) are because of the MHL 1 or MSH 2 genes. In a lower fraction of cases, another gene of the mismatch repair (MMR) machinery, MSH6, may be responsible. Families with MSH6 mutations are difficult to recognize, as microsatellite instability (MSI) may not be detectable and immunohistochemistry (IHC) may give ambiguous results. In the present study, we proposed (i) to determine the frequency of MSH6 mutations in a selected population of colorectal cancer patients obtained from a tumor registry, (ii) to assess whether IHC is a suitable tool for selecting and identifying MSH6 mutation carriers. One hundred neoplasms of the large bowel from suspected HNPCC families were analyzed for MSI (BAT 25 and BAT 26 markers) and immunohistochemical expression of the MSH6 protein. We found on 12 tumors (from different families) showing instability or lack of MSH6 expression. Among these, four potentially pathogenic MSH6 mutations were detected (del A at 2984; del TT at 3119; del AGG cod 385; and del CGT cod 1242) by direct gene sequencing. These represented 12.9% of all families with constitutional mutations of the DNA MMR genes. Thus, some 5% of all HNPCC families are featured by constitutional mutation of the MSH6 gene. This appears, however, as a minimum estimate; routine use of IHC and the study of large numbers of individuals and families with little or no evidence of Lynch syndrome might reveal that mutation of this gene account for a large fraction of HNPCC.

Impact of surgery on the development of duodenal cancer in patients with familial adenomatous polyposis.

PURPOSE: Precancerous duodenal lesions in patients with familial adenomatous polyposis can be detected with duodenoscopy and treatment may prevent the development of cancer. We proposed to determine the frequency, natural history, cumulative risk, and risk factors of the precancerous duodenal lesions in a series of patients diagnosed in northern Italy. METHODS: A prospective, endoscopic, follow-up protocol was performed in 50 patients examined by gastroduodenoscopy at two years of interval or less. The presence and severity of precancerous lesions of the duodenal mucosa were evaluated by Spigelman score. Twenty-five patients (50 percent) had proctocolectomy and ileoanal anastomosis, 15 (30 percent) had colectomy and ileorectal anastomosis, and 5 (10 percent) had proctocolectomy and definitive ileostomy from 0 to 3 years before the admission to the surveillance program. All patients showed more than a thousand adenomas in the colorectal mucosa. No patients with attenuated polyposis were found. RESULTS: At the first endoscopy, duodenal adenomas could be detected in 19 of 50 patients (38 percent), whereas at the end of the follow-up, 43 (86 percent) had duodenal lesions. The final mean Spigelman score increased during the follow-up period (P<0.001 respect to baseline values). No duodenal cancer could be detected. Eleven patients had or developed severe precancerous duodenal lesions (Stage IV) treated with endoscopic or surgical resection. The distribution of patients with Stage IV according to the surgery of the colon was: 2 of 25 treated with ileoanal anastomosis and 8 of 15 with ileorectal anastomosis (P=0.0024, Fisher's exact test). CONCLUSIONS: Patients with familial adenomatous polyposis are at risk of significant neoplasia. The natural history of precancerous lesions might be related to surgical treatment of colorectal neoplasms.

A genetic model for determining MSH2 and MLH1 carrier probabilities based on family history and tumor microsatellite instability.

Mutation-predicting models can be useful when deciding on the genetic testing of individuals at risk and in determining the cost effectiveness of screening strategies at the population level. The aim of this study was to evaluate the performance of a newly developed genetic model that incorporates tumor microsatellite instability (MSI) information, called the AIFEG model, and in predicting the presence of mutations in MSH2 and MLH1 in probands with suspected hereditary non-polyposis colorectal cancer. The AIFEG model is based on published estimates of mutation frequencies and cancer penetrances in carriers and non-carriers and employs the program MLINK of the FASTLINK package to calculate the proband's carrier probability. Model performance is evaluated in a series of 219 families screened for mutations in both MSH2 and MLH1, in which 68 disease-causing mutations were identified. Predictions are first obtained using family history only and then converted into posterior probabilities using information on MSI. This improves predictions substantially. Using a probability threshold of 10% for mutation analysis, the AIFEG model applied to our series has 100% sensitivity and 71% specificity.

Attenuated familial adenomatous polyposis and Muir-Torre syndrome linked to compound biallelic constitutional MYH gene mutations.

Attenuated familial adenomatous polyposis and Muir-Torre syndrome linked to compound biallelic constitutional MYH gene mutations.Peculiar dermatologic manifestations are present in several heritable gastrointestinal disorders. Muir-Torre syndrome (MTS) is a genodermatosis whose peculiar feature is the presence of sebaceous gland tumors associated with visceral malignancies. We describe one patient in whom multiple sebaceous gland tumors were associated with early onset colon and thyroid cancers and attenuated polyposis coli. Her family history was positive for colonic adenomas. She had a daughter presenting with yellow papules in the forehead region developed in the late infancy. Skin and visceral neoplasms were tested for microsatellite instability and immunohistochemical status of mismatch repair (MMR), APC and MYH proteins. The proband colon and skin tumors were microsatellite stable and showed normal expression of MMR proteins. Cytoplasmic expression of MYH protein was revealed in colonic cancer cells. Compound heterozygosity due to biallelic mutations in MYH, R168H and 379delC, was identified in the proband. The 11-year-old daughter was carrier of the monoallelic constitutional mutation 379delC in the MYH gene; in the sister, the R168H MYH gene mutation was detected. This report presents an interesting case of association between MYH-associated polyposis and sebaceous gland tumors. These findings suggest that patients with MTS phenotype that include colonic polyposis should be screened for MYH gene mutations.

Different phenotypes in Muir-Torre syndrome: clinical and biomolecular characterization in two Italian families.

The Muir-Torre syndrome (MTS) is an autosomal dominant genodermatosis characterized by the presence of sebaceous gland tumours, with or without keratoacanthomas, associated with visceral malignancies. We describe and characterize two families in which the ample phenotypic variability of MTS was evident. After clinical evaluation, the skin and visceral tumours of one member of a family with 'classic' MTS and one member of a family with a 'peculiar' MTS phenotype without sebaceous lesions, but with only multiple keratoacanthomas, were analysed for microsatellite instability (MSI) and by immunohistochemistry. Tumours of both individuals showed MSI, with a concomitant lack of MSH2 immunostaining in all evaluated skin and visceral lesions; moreover, in the proband of family 2 a constitutional mutation (C-->T substitution leading to a stop codon) in the MSH2 gene was identified. We conclude that the diagnosis of MTS, which is mainly clinical, should take into account an ample phenotypic variability, which includes both cases with typical cancer aggregation in families and cases characterized by the association of visceral malignancies with multiple keratoacanthomas (without sebaceous lesions), without an apparent family history of cancer.

Survival differences between European and US patients with colorectal cancer: role of stage at diagnosis and surgery.

BACKGROUND: Population based colorectal cancer survival among patients diagnosed in 1985-89 was lower in Europe than in the USA (45% v 59% five year relative survival). AIMS: To explain this difference in survival using a new analytic approach for patients diagnosed between 1990 and 1991. SUBJECTS: A total of 2492 European and 11 191 US colorectal adenocarcinoma patients registered by 10 European and nine US cancer registries. METHODS: We obtained clinical information on disease stage, number of lymph nodes examined, and surgical treatment. We analysed three year relative survival, calculating relative excess risks of death (RERs, referent category US patients) adjusted for age, sex, site, surgery, stage, and number of nodes examined, using a new multivariable approach. RESULTS: We found that 85% of European patients and 92% of US patients underwent surgical resection. Three year relative survival was 69% for US patients and 57% for European patients. After adjustment for age, sex, and site, the RER was significantly high in all 10 European populations, ranging from 1.07 (95% confidence interval 0.86-1.32) (Modena, Italy) to 2.22 (1.79-2.76) (Thames, UK). After further adjustment for stage, surgical resection, and number of nodes examined (a determinant of stage), RERs ranged from 0.77 (0.62-0.96) to 1.59 (1.28-1.97). For some European registries the excess risk was small and not statistically significant. CONCLUSIONS: US-Europe survival differences in colorectal cancer are large but seem to be mostly attributable to differences in stage at diagnosis. There are wide variations in diagnostic and surgical practice between Europe and the USA.

Trend of incidence, subsite distribution and staging of colorectal neoplasms in the 15-year experience of a specialised cancer registry.

BACKGROUND: Two-thirds of colorectal malignancies are localised in the left colon and rectum. Recent studies suggest a trend towards an increase of right-sided tumours which might have important implications for screening and surveillance. A colorectal cancer registry was set up in Modena, northern Italy, with the purpose of examining incidence, subsite distribution and staging of colorectal malignancies over a 15-year period. PATIENTS AND METHODS: From 1984 to 1998, 2517 tumours in 2462 patients were detected and staged with the tumour node metastasis (TNM) system. The 'right colon' was considered from caecum to splenic flexure; the 'left colon' included descending and sigmoid colon; and the 'rectum' included rectosigmoid junction, ampulla and anus. RESULTS: Cancer incidence showed an overall increase. Considering the various subsites, an increase of 33.7% in all colonic segments was shown whereas rectal tumours tended to decline. TNM staging showed a gradual increase of localised lesions (41.2% in 1984 versus 53.3% in 1998), with a proportional reduction of advanced tumours. CONCLUSIONS: Our study indicates an increase of tumour incidence in all colonic segments more than a shift to the right colon. TNM staging tended to improve with an appreciable increase of localised lesions. These findings could be consequent to a more extensive use of colonoscopy.

Genetic testing among high-risk individuals in families with hereditary nonpolyposis colorectal cancer.

Hereditary nonpolyposis colorectal cancer (HNPCC) is frequently associated with constitutional mutations in a class of genes involved in DNA mismatch repair. We identified 32 kindreds, with germline mutations in one of three genes hMSH2, hMLH1 or hMSH6. In this study, we purposed to evaluate how many high-risk individuals in each family underwent genetic testing: moreover, we assessed how many mutation-positive unaffected individuals accepted colonoscopic surveillance and the main findings of the recommended follow-up. Families were identified through a population-based registry, or referred from other centres. Members of the families were invited for an education session with two members of the staff. When a kindred was consistent with HNPCC, neoplastic tissues were examined for microsatellite instability (MSI) and immunohistochemical expression of MSH2, MLH1 and MSH6 proteins. Moreover, constitutional mutations were searched by SSCP or direct sequencing of the whole genomic region. Of the 164 subjects assessed by genetic testing, 89 were gene carriers (66 affected - that is, with HNPCC-related cancer diagnosis - and 23 unaffected) and 75 tested negative. Among the 23 unaffected gene carriers, 18 (78.3%) underwent colonoscopy and four declined. On a total of 292 first degree at risk of cancer, 194 (66.4%) did not undergo genetic testing. The main reasons for this were: (a) difficulty to reach family members at risk, (b) lack of collaboration, (c) lack of interest in preventive medicine or 'fatalistic' attitude towards cancer occurrence. The number of colorectal lesions detected at endoscopy in gene carriers was significantly (P<0.01) higher than in controls (noncarriers). We conclude that a large fraction of high-risk individuals in mutation-positive HNPCC families does not undergo genetic testing, despite the benefits of molecular screening and endoscopic surveillance. This clearly indicates that there are still barriers to genetic testing in HNPCC, and that we are unable to provide adequate protection against cancer development in these families.

Aetiology of colorectal cancer and relevance of monogenic inheritance.

BACKGROUND AND AIMS: Although diet and lifestyle are associated with the development of colorectal malignancies, the only clearly identified aetiological factors in colorectal cancer are inheritance (hereditary non-polyposis colorectal cancer (HNPCC) and familial polyposis), inflammatory bowel diseases, papillomavirus, and acquired immunodeficiency syndrome (AIDS). Our aim was to determine what proportion of colorectal neoplasms could be attributed to these specific factors. PATIENTS AND METHODS: Data from a colorectal cancer registry were analysed over a 15 year period, during which nearly 2500 cases were recorded. In patients with suspected HNPCC, microsatellite instability and immunohistochemical expression of proteins encoded by the main DNA mismatch repair genes were assessed. In families with unstable neoplasms, constitutional mutations of the mismatch repair genes hMSH2, hMLH1, and hMSH6 were evaluated by single strand conformation polymorphism analysis and sequencing. RESULTS: Inflammatory bowel diseases, familial polyposis, and AIDS were rare causes of colorectal cancer (three, three, and one case, respectively). Anal squamous carcinoma developed in 27 patients (1.0%) and could be attributed to papillomavirus infection. In 58 patients (from 34 families) a clinical diagnosis of HNPCC was established (2.4%). In total, cases with a known aetiology were 92 (3.7% of all patients). Microsatellite instability was detected in 15 cancers from HNPCC families, and germline mutations in six families (12 patients, 0.5% of the total). Families with unstable tumours, with or without mutations, were clinically similar, suggesting the involvement of the mismatch repair system even when mutations were not detected. CONCLUSIONS: The study suggests that the aetiology of colorectal malignancies remains elusive in the large majority of cases. Among specific causes, HNPCC represents the most frequent. However, with a population based approach, constitutional mutations of the main genes involved in HNPCC can be detected in only 20% of cases.

The role of hPMS1 and hPMS2 in predisposing to colorectal cancer.

Hereditary nonpolyposis colorectal cancer (HNPCC) is attributable to a deficiency of mismatch repair. Inactivation of DNA mismatch repair underlies the genesis of microsatellite instability in colorectal cancer. Germline mutations in three DNA mismatch repair genes, hMSH2, hMLH1, and hMSH6, have been found to segregate in HNPCC and HNPCC-like families. The two DNA mismatch repair genes hPMS1 and hPMS2 have also been suggested to predispose to HNPCC. In this study, 84 HNPCC and HNPCC-like kindreds without known mutations in the other three known DNA mismatch repair genes were screened for germline mutations in the hPMS1 or hPMS2 gene. No clear-cut pathogenic mutations were identified. Conversion technology was used to detect a large hMSH2 deletion in two affected members of the kindred in which the hPMS1 mutation was originally reported, whereas the hPMS1 mutation was only present in one of these two individuals. Since the hPMS1 and hPMS2 genes were first reported, germline mutations in hPMS2 have been demonstrated primarily in patients with Turcot's syndrome. However, no mutation in any of the two genes has been found to segregate in HNPCC families. Until there is better evidence for an increased colorectal cancer risk associated with germline mutations in these genes, a conservative interpretation of the role of mutations in these genes is advised.

Phenotype-genotype correlations in an extended family with adenomatosis coli and an unusual APC gene mutation.

PURPOSE: Genotype-phenotype correlations in familial adenomatous polyposis are only partially understood and, in particular, little is known about the biomolecular characteristics of desmoid tumors, which are one of the most serious and frequent manifestations of familial adenomatous polyposis. In the present study, we describe a family with familial adenomatous polyposis, with peculiar clinical characteristics (i.e., frequency and severity of desmoid neoplasms) associated with an unusual mutation of the adenomatosis polyposis coli gene. If confirmed by other investigations, these findings might help to understand the biologic mechanisms by which specific adenomatosis polyposis coli mutations predispose to desmoid tumors. METHODS: The family with familial adenomatous polyposis, living in southern Italy, was studied from 1985 to the end of 1999; at this date, 15 individuals have been affected by histologically verified familial adenomatous polyposis, 11 of whom had desmoid tumors. A total of 19 family members were studied for adenomatosis polyposis coli gene mutations; 13 of them tested positive and 6 negative. The analytical procedure-previously described-consisted of the extraction of peripheral blood cell DNA, amplification of exon 15 by polymerase chain reaction, single-strand conformation polymorphism analysis, and direct sequencing of the DNA fragment containing the mutation. RESULTS: The main clinical features of the family were 1) a high frequency of desmoid tumors and, consequently, a high penetrance of the desmoid trait in all branches of the family and in 11 (73.3 percent) of 15 affected individuals and 2) severity of desmoids in at least 4 family members, 2 of whom died for causes related to the presence of these tumors. The molecular basis of the disease was an uncommon mutation of the adenomatosis polyposis coli gene, consisting of a large deletion of 310 base pairs at codon 1,464, with duplication of the breakpoint (4,394ins15del310), leading to a stop codon at position 1,575. CONCLUSIONS: The present study shows that a truncating mutation in the adenomatosis polyposis coli gene at the beginning of the region frequently associated with desmoids induced a familial adenomatous polyposis phenotype featured by a high penetrance of the desmoid trait, with severe disease in several affected members of both sexes. The study may help to understand the biologic mechanisms of genotype-phenotype correlations in adenomatosis coli.

Molecular screening for hereditary nonpolyposis colorectal cancer: a prospective, population-based study.

PURPOSE: Germline mutations in mismatch repair genes predispose to hereditary nonpolyposis colorectal cancer (HNPCC). To address effective screening programs, the true incidence of the disease must be known. Previous clinical investigations reported estimates ranging between 0.5% and 13% of all the colorectal cancer (CRC) cases, whereas biomolecular studies in Finland found an incidence of 2% to 2.7% of mutation carriers for the disease. The aim of the present report is to establish the frequency of the disease in a high-incidence area for colon cancer. PATIENTS AND METHODS: Through the data of the local CRC registry, we prospectively collected all cases of CRC from January 1, 1996, through December 31, 1997 (N = 391). Three hundred thirty-six CRC cases (85.9% of the incident cases) were screened for microsatellite instability (MSI) with six to 12 mono- and dinucleotide markers. MSI cases were subjected to MSH2 and MLH1 germline mutation analysis and immunohistochemistry; the methylation of the promoter region was studied for MLH1. RESULTS: Twenty-eight cases (8.3% of the total) showed MSI. MSI cases differed significantly from microsatellite-stable (MSS) cases for their proximal location (P <.01), high mucinous component (P <.01), and poor differentiation (P =.002). Of MSI cases studied (n = 12), only one with a family history compatible with HNPCC had a germline mutation (in MSH2). Five other patients with a family history of HNPCC (two with MSI and three with MSS tumors) did not show germline mutations. CONCLUSION: We conclude that the incidence of molecularly confirmed HNPCC (one [0.3%] of 336) in a high-incidence area for CRC is lower than in previous biomolecular and clinical estimates.