Clinical implications of genetic testing in familial intermediate and late-onset colorectal cancer.

The genetic background of familial, late-onset colorectal cancer (CRC) (i.e., onset > age 50 years) has not been studied as thoroughly as other subgroups of familial CRC, and the proportion of families with a germline genetic predisposition to CRC remains to be defined. To define the contribution of known or suggested CRC predisposition genes to familial late-onset CRC, we analyzed 32 well-established or candidate CRC predisposition genes in 75 families with late-onset CRC. We identified pathogenic or likely pathogenic variants in five patients in MSH6 (n = 1), MUTYH (monoallelic; n = 2) and NTHL1 (monoallelic; n = 2). In addition, we identified a number of variants of unknown significance in particular in the lower penetrant Lynch syndrome-associated mismatch repair (MMR) gene MSH6 (n = 6). In conclusion, screening using a comprehensive cancer gene panel in families with accumulation of late-onset CRC appears not to have a significant clinical value due to the low level of high-risk pathogenic variants detected. Our data suggest that only patients with abnormal MMR immunohistochemistry (IHC) or microsatellite instability (MSI) analyses, suggestive of Lynch syndrome, or a family history indicating another cancer predisposition syndrome should be prioritized for such genetic evaluations. Variants in MSH6 and MUTYH have previously been proposed to be involved in digenic or oligogenic hereditary predisposition to CRC. Accumulation of variants in MSH6 and monoallelic, pathogenic variants in MUTYH in our study indicates that digenic or oligogenic inheritance might be involved in late-onset CRC and warrants further studies of complex types of inheritance.

Double somatic mismatch repair gene pathogenic variants as common as Lynch syndrome among endometrial cancer patients.

OBJECTIVE: Lynch syndrome is the most common cause of inherited endometrial cancer, attributable to germline pathogenic variants (PV) in mismatch repair (MMR) genes. Tumor microsatellite instability (MSI-high) and MMR IHC abnormalities are characteristics of Lynch syndrome. Double somatic MMR gene PV also cause MSI-high endometrial cancers. The aim of this study was to determine the relative frequency of Lynch syndrome and double somatic MMR PV. METHODS: 341 endometrial cancer patients enrolled in the Ohio Colorectal Cancer Prevention Initiative at The Ohio State University Comprehensive Cancer Center from 1/1/13-12/31/16. All tumors underwent immunohistochemical (IHC) staining for the four MMR proteins, MSI testing, and MLH1 methylation testing if the tumor was MMR-deficient (dMMR). Germline genetic testing for Lynch syndrome was undertaken for all cases with dMMR tumors lacking MLH1 methylation. Tumor sequencing followed if a germline MMR gene PV was not identified. RESULTS: Twenty-seven percent (91/341) of tumors were either MSI-high or had abnormal IHC indicating dMMR. As expected, most dMMR tumors had MLH1 methylation; (69, 75.8% of the dMMR cases; 20.2% of total). Among the 22 (6.5%) cases with dMMR not explained by methylation, 10 (2.9% of total) were found to have Lynch syndrome (6 MSH6, 3 MSH2, 1 PMS2). Double somatic MMR PV accounted for the remaining 12 dMMR cases (3.5% of total). CONCLUSIONS: Since double somatic MMR gene PV are as common as Lynch syndrome among endometrial cancer patients, paired tumor and germline testing for patients with non-methylated dMMR tumor may be the most efficient approach for LS screening.

Molecular Features and Clinical Management of Hereditary Gynecological Cancers.

Hereditary gynecological cancers are caused by several inherited genes. Tumors that arise in the female reproductive system, such as ovaries and the uterus, overlap with hereditary cancers. Several hereditary cancer-related genes are important because they might lead to therapeutic targets. Treatment of hereditary cancers should be updated in line with the advent of various new methods of evaluation. Next-generation sequencing has led to rapid, economical genetic analyses that have prompted a concomitant and significant paradigm shift with respect to hereditary cancers. Molecular tumor profiling is an epochal method for determining therapeutic targets. Clinical treatment strategies are now being designed based on biomarkers based on tumor profiling. Furthermore, the National Comprehensive Cancer Network (NCCN) guidelines significantly changed the genetic testing process in 2020 to initially consider multi-gene panel (MGP) evaluation. Here, we reviewed the molecular features and clinical management of hereditary gynecological malignancies, such as hereditary breast and ovarian cancer (HBOC), and Lynch, Li-Fraumeni, Cowden, and Peutz-Jeghers syndromes. We also reviewed cancer-susceptible genes revealed by MGP tests.

Comparison of two Lynch screening strategies in endometrial cancer in a California health system.

OBJECTIVE: Compare detection of Lynch syndrome in endometrial cancer between regions of a health care system with different screening strategies. METHODS: A retrospective study of endometrial cancer (EC) cases from 2 regions of an integrated health care system (Kaiser Permanente Northern (KPNC) and Southern (KPSC) California). Within KPNC, immunohistochemistry tumor screening (IHC) was physician ordered and risk-based; within KPSC, IHC was universal and automated. Clinical risk factors associated with abnormal IHC and Lynch Syndrome (LS) were identified. RESULTS: During the study, there were 2045 endometrial cancers: 1399 in the physician-order group and 646 in the universal testing group. In the physician-order group: among women < age 60, 34% underwent IHC; 9.6% were abnormal, and 3% were possible LS after methylation testing; among women ≥60, 11% underwent IHC, 3% were abnormal and <1% were possible LS. In the universal group, 87% of women age <60 had IHC, 19.4% were abnormal, and 6% were possible LS; Among women age ≥60, 82% underwent IHC, 26% were abnormal, and 2% were possible LS. There were no differences in LS cases between the physician-order group and the universal group in either age strata (<60: 3% vs. 3.6%, p=0.62; ≥60: <1% vs. 1%, p=0.63) Factors associated with LS were younger age (odds ratio (OR) 0.11, 95% confidence interval (CI) 0.04-0.29) and lower body mass index (BMI), (OR 0.38 95% CI 0.18-0.80). CONCLUSIONS: Universal IHC screening did not result in increased LS detection in EC.

A Novel Germline MLH1 In-Frame Deletion in a Slovenian Lynch Syndrome Family Associated with Uncommon Isolated PMS2 Loss in Tumor Tissue.

The diagnostics of Lynch syndrome (LS) is focused on the detection of DNA mismatch repair (MMR) system deficiency. MMR deficiency can be detected on tumor tissue by microsatellite instability (MSI) using molecular genetic test or by loss of expression of one of the four proteins (MLH1, MSH2, MSH6, and PMS2) involved in the MMR system using immunohistochemistry (IHC) staining. According to the National Comprehensive Cancer Network (NCCN) guidelines, definitive diagnosis of LS requires the identification of the germline pathogenic variant in one of the MMR genes. In the report, we are presenting interesting novel MLH1 in-frame deletion LRG_216t1:c.2236_2247delCTGCCTGATCTA p.(Leu746_Leu749del) associated with LS. The variant appears to be associated with uncommon isolated loss of PMS2 immunohistochemistry protein staining (expression) in tumor tissue instead of MLH1 and PMS2 protein loss, which is commonly seen with pathogenic variants in MLH1. The variant was classified as likely pathogenic, based on segregation analysis and molecular characterization of blood and tumor samples. According to the American College of Medical Genetics (ACMG) guidelines, the following evidence categories of PM1, PM2, PM4, and PP1 moderate have been used for classification of the novel variant. By detecting and classifying the novel MLH1 variant as likely pathogenic, we confirmed the LS in this family.

Microsatellite instability in colorectal cancer: overview of its clinical significance and novel perspectives.

Microsatellite instability (MSI) is a key biomarker in colorectal cancer (CRC), with crucial diagnostic, prognostic, and predictive implications. Testing for mismatch repair deficiency (MMR-D)/MSI is recommended during screening for Lynch syndrome, an autosomal-dominant hereditary disease that is characterized by germline mutations in the MMR genes and associated with an increased risk for several types of cancer. Additionally, MSI-high (MSI-H) status is associated with a better prognosis in early-stage CRC and a lack of benefit from adjuvant treatment with 5-fluorouracil in stage II disease. More recently, MSI has emerged as a predictor of sensitivity to immunotherapy-based treatments. The groundbreaking success of checkpoint inhibitors in MMR-D metastatic CRC has opened a new therapeutic scenario for patients with these tumors. MSI-H CRC, in both the sporadic and hereditary settings, is characterized by distinctive molecular and clinicopathologic features and represents a unique subset of CRC that is the object of growing interest and fervent research efforts. This article, an overview of the expanding role of MSI in CRC, covers its clinical significance, the available data on molecular profiling, novel perspectives on MSI testing, biomarkers in MSI-H CRC, immunotherapy resistance, and novel immunotherapy strategies.

Recording of family history is associated with colorectal cancer stage.

BACKGROUND: Colorectal cancer (CRC) associated with Lynch syndrome usually presents at a relatively young age. The Revised Bethesda Guidelines advise screening for Lynch syndrome in patients diagnosed with CRC and a positive family history (FH) of CRC and other Lynch-related cancers. OBJECTIVE: To evaluate recording of the FH and identify factors associated with recording in young patients with CRC. PATIENTS AND METHODS: In one academic and two nonacademic hospitals, of all patients diagnosed with CRC at the age of 60 years or younger between 1999 and 2007, electronic medical records were evaluated for a recorded FH of CRC and other Lynch-related cancers. Patient and tumor characteristics were retrieved from the Dutch Comprehensive Cancer Centre and the Dutch Pathological Archive. RESULTS: A total of 676 patients were identified. FH was recorded in 395/676 (58%) patients. From 1999 to 2007, recording improved with an odds ratio (OR) of 1.10 [95% confidence interval (CI) 1.03-1.17] per year. Stage III CRC (OR 1.71, 95% CI 1.07-2.75) and administration of chemotherapy (OR 1.84, 95% CI 1.17-2.89) were associated with recording in multivariate analysis. Other factors, including age at diagnosis, sex, surgery, radiotherapy, proximal tumor localization, poor differentiation, and mucinous histology, were not associated with recording. CONCLUSION: A FH of CRC and other Lynch-related cancers was not recorded in ∼40% of young CRC patients and recording improved only slightly over the years. As a first step in the identification of Lynch-related cancer families, physicians should be trained to record a detailed FH in the work-up of all newly diagnosed CRC patients.

Reflex immunohistochemistry and microsatellite instability testing of colorectal tumors for Lynch syndrome among US cancer programs and follow-up of abnormal results.

PURPOSE: Immunohistochemistry (IHC) for MLH1, MSH2, MSH6, and PMS2 protein expression and microsatellite instability (MSI) are well-established tools to screen for Lynch syndrome (LS). Although many cancer centers have adopted these tools as reflex LS screening after a colorectal cancer diagnosis, the standard of care has not been established, and no formal studies have described this practice in the United States. The purpose of this study was to describe prevalent practices regarding IHC/MSI reflex testing for LS in the United States and the subsequent follow-up of abnormal results. MATERIALS AND METHODS: A 12-item survey was developed after interdisciplinary expert input. A letter of invitation, survey, and online-survey option were sent to a contact at each cancer program. A modified Dillman strategy was used to maximize the response rate. The sample included 39 National Cancer Institute-designated Comprehensive Cancer Centers (NCI-CCCs), 50 randomly selected American College of Surgeons-accredited Community Hospital Comprehensive Cancer Programs (COMPs), and 50 Community Hospital Cancer Programs (CHCPs). RESULTS: The overall response rate was 50%. Seventy-one percent of NCI-CCCs, 36% of COMPs, and 15% of CHCPs were conducting reflex IHC/MSI for LS; 48% of the programs used IHC, 14% of the programs used MSI, and 38% of the programs used both IHC and MSI. One program used a presurgical information packet, four programs offered an opt-out option, and none of the programs required written consent. CONCLUSION: Although most NCI-CCCs use reflex IHC/MSI to screen for LS, this practice is not well-adopted by community hospitals. These findings may indicate an emerging standard of care and diffusion from NCI-CCC to community cancer programs. Our findings also described an important trend away from requiring written patient consent for screening.

[Lynch syndrome and microsatellite instability: a review]. / Le syndrome de Lynch et l'instabilité des microsatellites: revue de littérature.

Microsatellite instability (MSI) phenotype occurs in approximately 15 to 24% of colorectal cancer (CRC) patients and may be sporadic or hereditary. It reflects a mutator phenotype in the tumor due to a lack of mismatch repair system. MSI is indeed one of the characteristics of CRCs occurring in Lynch syndrome and some sporadic cases. CRCs with MSI have a better prognosis than CRCs with microsatellite stability (MSS). This is explained partly by a more important anti-tumor immune response and by apoptosis of tumor cells in which mutations accumulate. However, in some retrospective studies, microsatellite instability in stage II CRCs was associated with no benefit to or even a deleterious effect of 5-FU alone based adjuvant therapy. Nevertheless, results obtained in stage III CRCs with FOLFOX type adjuvant chemotherapy remain favorable in retrospective studies.

Microsatellite instability and colorectal cancer.

CONTEXT: About 15% of colorectal cancers are characterized by genomic microsatellite instability, and of these, about 1 in 5 (2%-4% overall) are due to Lynch syndrome, a dominantly inherited condition predisposing the patient to cancers of multiple organ systems, including the gastrointestinal tract. Identification of individuals with Lynch syndrome allows for increased surveillance of the affected individual and of potentially affected family members. OBJECTIVE: To review the literature on microsatellite instability in colorectal cancer and current laboratory diagnostic testing strategies for the detection of Lynch syndrome. DATA SOURCES: This review is based on peer-reviewed literature, published guidelines from professional organizations (Evaluation of Genomic Applications in Practice and Prevention Working Group, National Comprehensive Cancer Network), and information from clinical laboratories performing microsatellite instability testing. CONCLUSIONS: Universal screening for Lynch syndrome in all individuals affected with colorectal cancer has been recommended by the Evaluation of Genomic Applications in Practice and Prevention Working Group. Preliminary screening tests can identify individuals unlikely to be affected by Lynch syndrome, thereby reducing the need for full gene analysis. Immunohistochemistry and polymerase chain reaction-based tests for microsatellite instability have similar clinical sensitivity and specificity, and each method has advantages and limitations. BRAF and MLH1 methylation testing are useful reflex tests for those with a defect in MLH1 identified by immunohistochemistry. Emerging technologies, such as high-throughput sequencing, may substantially affect diagnostic algorithms in the future.

[Microsatellite instability. A new predictive marker (?)]. / Mikrosatelliteninstabilität. Ein neuer prädiktiver Marker (?).

Microsatellite instability (MSI) is a hallmark of hereditary non-polyposis colorectal cancer (HNPCC), but also occurs in about 12%-15% of sporadic colorectal cancer (CRC) where it is a consequence of an epigenetic inactivation of MLH1. High frequency MSI (MSI-H; i.e. at least two of five specified microsatellite markers show instability) was shown in a large meta-analysis and in recent trials to be a positive prognostic marker for overall survival in CRC. MSI-H or mismatch repair deficiency (MMRD) was also shown to be a marker for ineffectiveness of adjuvant 5-fluorouracil (5-FU) based chemotherapy in CRC. At present, there are no guidelines defining the need for microsatellite analysis before chemotherapy. However, studies published to date provide data suggesting that MSI-H CRC patients should not receive adjuvant chemotherapy, with the exception of patients with other factors or poor prognosis (e.g. T4 tumors, G3/G4 status, blood or lymphatic vessel invasion). MSI or MMRD testing can contribute to a more individualized therapy of CRC and should be performed prior to planned 5-FU monotherapy or adjuvant chemotherapy in a non-metastatic setting.

Bowel preparation and colonoscopy technique to detect non-polypoid colorectal neoplasms.

Colonoscopy is considered the gold standard for colon cancer screening. In a recent study, however, 0.3% to 0.9% patients developed colorectal cancer within 3 years after removal of adenomas. Some reasons for the development of interval colorectal cancers include missed or incompletely removed lesions during the initial colonoscopy. Non-polypoid colorectal neoplasms are a potential contributor to the pool of missed lesions because they can be easily missed as a result of inadequate colon preparation or examination technique. This article discusses the methods that are useful to improve the quality of bowel preparation and examination technique.

Development of expertise in the detection and classification of non-polypoid colorectal neoplasia: Experience-based data at an academic GI unit.

At its core, quality improvement in gastrointestinal (GI) practice relies on continuous training, education, and information among all health care providers, whether gastroenterologists, GI trainees, endoscopy nurses, or GI pathologists. Over the past few years, it became clear that objective criteria are needed to assess the quality of colonoscopy, such as cecum intubation rate, quality of bowel preparation, withdrawal time, and adenoma detection rate. In this context, development of competence among practicing endoscopists to adequately detect and treat non-polypoid colorectal neoplasms (NP-CRNs) deserves special attention. We describe a summary of the path to develop expertise in detection and management of NP-CRNs, based on experience at our academic GI unit.

Exploring the potential chemopreventative effect of aspirin and rofecoxib on hereditary nonpolyposis colorectal cancer-like endometrial cancer cells in vitro through mechanisms involving apoptosis, the cell cycle, and mismatch repair gene expression.

Women in hereditary nonpolyposis colorectal cancer (HNPCC) families have up to a 71% lifetime risk for developing endometrial cancer (EC). This compares to the female lifetime risk for colorectal cancer (CRC) in HNPCC of 60%. The basis of HNPCC is an inherited mutation in a mismatch repair gene (MMR). Aspirin and COX2 inhibitors seem to have a chemoprotective effect on CRC in the general population and are the subject of prospective clinical studies in patients at high risk for CRC including HNPCC. There is no evidence that these agents have any protective effect against EC in the general population. This study investigated the effect of aspirin and a COX2 inhibitor (rofecoxib) on an HNPCC EC cell line model (Ishikawa) by assessing the effect on proliferation, apoptosis, the cell cycle, and MMR gene expression. Aspirin inhibits EC cell proliferation by inducing apoptosis and changes in the cell cycle. This effect is not mediated by changes in MMR gene (hMSH2) expression as assessed by quantitative reverse transcription-polymerase chain reaction. Rofecoxib inhibits EC cell proliferation; this did not appear to be mediated by induction of apoptosis, by alterations of the cell cycle, or by changes in MMR gene expression.

An appendix carcinoid tumor in a patient with hereditary nonpolyposis colorectal cancer.

Gastrointestinal carcinoid tumors are often associated with other tumors, particularly colon adenocarcinomas; but the association between carcinoid tumors and hereditary nonpolyposis colorectal cancer (HNPCC) syndrome has not yet been explored. We report an unusual case of a 28-year-old woman with HNPCC who underwent surgery for a transverse colon adenocarcinoma in whom an appendix carcinoid tumor was incidentally found. To assess whether the carcinoid tumor displayed the characteristic molecular features of HNPCC tumors, we investigated the expression of mismatch-repair (MMR) proteins and microsatellite instability (MSI) status in both tumors. Both tumors demonstrated normal expression of the MMR proteins hMLH1, hMSH2, hMSH6, and hPMS2. Interestingly, the adenocarcinoma exhibited an MSI phenotype but the carcinoid tumor did not, indicating that these 2 tumors arose through different molecular pathways.

Survival after adjuvant 5-FU treatment for stage III colon cancer in hereditary nonpolyposis colorectal cancer.

In vitro studies suggest that a deficient mismatch repair (MMR) system reduces 5-Fluorouracil cytotoxicity. Colon cancer (CC) in hereditary nonpolyposis colorectal cancer (HNPCC) is due to a dysfunctioning MMR gene that leads to microsatellite instability (MSI). Clinical studies on the efficacy of 5-Fluorouracil (5-FU) in MSI high tumours are contradictory. In a retrospective study, we compared the survival of subjects with stage III CC from HNPCC families that were treated with and without adjuvant 5-FU. The Dutch HNPCC family registry was used. Information on adjuvant chemotherapy for stage III CC was obtained from subjects of families with a mutation and/or who fulfilled the AMS criteria or who were strongly suspicious for HNPCC. CC specific survival was calculated. Observation time was measured either until the date of death, date of a second primary CC or until the closing date of the study, i.e., June 1, 2001. Statistical analysis was done by Kaplan-Meier survival analysis. A total of 92 subjects with stage III CC were included. Twenty-eight of them (17 males) had adjuvant treatment with 5-FU. The median follow-up was 4 (range: 1-17) years; 8 subjects died of CC. The 5-year survival was 70% (95% Cl: 49-90). Sixty-four subjects (36 males) did not have adjuvant therapy. Their median follow-up was 6 (range: 0-23) years. Twenty of them died of CC. The 5-year survival in this group was also 70% (95% Cl: 59-83). To date, the selection of patients with CC for 5-FU treatment is based on the stage rather than the biology of the tumour. In our study, the 5-year survival of subjects treated with and without adjuvant 5-FU did not differ. Further studies are necessary to elucidate the role of MSI in 5-FU treatment of MSI-H tumours in HNPCC.

Colon polyps and cancer.

During 1999-2000, a number of important issues related to endoscopy and colorectal polyps and cancer were investigated. Several papers consider whether flat adenomas with high malignant potential are as common in the West as in Japan. Clinical series indicate that signs of rectal bleeding are more predictive of colorectal cancer than gastrointestinal symptoms. Colonoscopy is more accurate than double-contrast barium enema for detecting polyps, and virtual colonoscopy is a promising new diagnostic and screening technique. Primary prevention dietary studies using adenoma recurrence as an end point yield negative results. Surveillance colonoscopy protects individuals in families with hereditary nonpolyposis colorectal cancer, but gastroenterologists continue to perform cancer surveillance in patients with ulcerative colitis in an inconsistent manner. Screening for colorectal neoplasia with fecal occult blood tests and flexible sigmoidoscopy is being better defined and promoted, although many now advocate direct colonoscopy screening based on increasing indirect evidence of efficacy. Better methods of treating large sessile neoplasms are being developed and evaluated, and follow-up surveillance for adenoma patients increasingly is being tailored to individual patient risk.

Randomized, double-blinded, placebo-controlled intervention study with supplemental calcium in families with hereditary nonpolyposis colorectal cancer.

BACKGROUND: A high-fat diet has been recognized for some time as a major risk factor for colorectal cancer. It is thought that fat promotes this disease by increasing the levels of fatty and bile acids within the colon. These acids irritate and damage the epithelial cells of the colon. As a result of this cellular destruction, an increase in the rate of cellular proliferation occurs. Oral calcium supplementation has been proposed as a dietary intervention for individuals at high risk of colorectal cancer because of its ability to reduce rectal epithelial cell proliferation through the binding of fatty and bile acids. Placebo-controlled studies, however, have yielded varying results. PURPOSE: We conducted a randomized, double-blinded, placebo-controlled trial to test oral calcium supplementation in patients at high risk of developing hereditary nonpolyposis colorectal cancer. METHODS: Thirty subjects at risk for this cancer, with an increased epithelial cell proliferation along the colon and rectum, were randomly assigned to either a placebo group (n = 15) or a treatment group (n = 15). They received either oral calcium carbonate (CaCO3) supplements (1.5 g) or placebo (cellulose and starch) three times a day during a 12-week period. Colonic biopsy specimens (rectal, sigmoidal, and descending) were obtained prior to and after the intervention trial, during endoscopy, for determination of labeling index (LI) of whole crypts and crypt compartments by 5-bromo-2'-deoxyuridine incorporation and immunohistochemistry. Proportional bile acid compositions in duodenal bile and cytolytic activity of fecal water were also determined. All P values represent two-tailed tests of statistical significance. RESULTS: Statistically significant reductions, comparing before with after intervention, in rectal whole-crypt LI after receiving either calcium supplements (from 10.9% +/- 5.2% [mean +/- SD] to 6.2% +/- 1.5%; P < .02) or placebo (from 11.7% +/- 4.7% to 8.2% +/- 3.1%; P < .05) were observed. In the three bowel segments, no statistically significant differences were observed between the supplemental calcium and placebo groups. A statistically significant reduction in cytolytic activity was determined during calcium supplementation (from 57% +/- 41% to 32% +/- 30%; P < .05), whereas in the placebo group, it did not change (from 42% +/- 41% to 36% +/- 27%; P > .10). CONCLUSIONS: Oral calcium supplementation was shown to cause only a minor nonstatistically significant reduction of epithelial cell proliferation in the rectum, compared with placebo, and to have no effect on the same parameter in the sigmoid and descending colon in first-degree relatives of hereditary nonpolyposis colorectal cancer patients. IMPLICATION: These results cast doubt on the value of calcium supplementation in the prevention of colorectal cancer, especially in individuals already consuming an adequate amount of dietary calcium.

Screening for hereditary non-polyposis colorectal cancer: a study of 22 kindreds in The Netherlands.

PURPOSE: Identification of the hereditary non-polyposis colorectal carcinoma syndrome (HNPCC) is a basis for secondary prevention. The objectives of this study are to investigate the natural history of HNPCC and to assess the effect of screening. PATIENTS AND METHODS: Screening for colorectal carcinoma was performed in 22 HNPCC families (colonoscopy or double-contrast barium enema and sigmoidoscopy). The patients were subdivided into two groups. Group A comprised patients with colorectal cancer who were referred because they were symptomatic. Group B included family members of these patients who were found to have a colorectal lesion by screening. We compared these groups with respect to the stage of tumor growth. RESULTS: Histologic examination of the tumors in Group A (87 patients) revealed Dukes A carcinomas in six patients, Dukes B carcinomas in 37, Dukes C carcinomas in 21, and Dukes D carcinomas in 10 patients (classification unknown in 13 patients). In Group B (20 patients), adenoma was found in 14 and carcinoma in six patients (Dukes A in two and Dukes B in four patients). A total of 93 patients, including those whose tumors were detected by screening, had a colorectal carcinoma. The age at diagnosis ranged from 24 to 81 years (mean age: 46 years). The location of the colonic tumors was proximal in 60 percent. Multiple primary tumors were found in 26 percent. CONCLUSION: These results suggest that screening leads to the early detection of colorectal carcinomas and adenomas in asymptomatic members of HNPCC families. Screening should be initiated at the age of 20 and continued during the life of the individual. Careful examination of the right colon is indicated because of the frequent occurrence of tumors in the proximal colon. A subtotal colectomy is indicated at the time of diagnosis of the initial colon cancer because of the risk of multiple primary tumors.