Choice of management strategy for colorectal cancer based on a diagnostic immunohistochemical test for defective mismatch repair

Microsatellite instability in a population of sporadic colorectal cancers: correlation between genetic and pathological profiles

BACKGROUND

Tumours with high-frequency microsatellite instability exhibit unique genotype and phenotype features, whereas the difference between low-frequency microsatellite instability and apparently stable tumours is far from being clear.

AIMS

To identify distinctive genetic and pathological characteristics of low-frequency microsatellite instability tumours.

METHODS

Microsatellite instability status of 57 sporadic colorectal cancers and its correlation with genetic, pathological and clinical features was analysed.

RESULTS

High frequency microsatellite instability and low-frequency microsatellite instability and apparently stable cancers were different in terms of tumour localisation (p=0.015), frequency of APC mutations (p=0.012), occurrence of Crohn's-like/lymphoid reaction (p=0.0353) and morphological evidence of origin from an adenoma (p=0.0338). Specifically, in low-frequency microsatellite instability cancers, APC mutations were very frequent (76.9%, 10/13) and a Crohn's-like/lymphoid reaction was common (38.5%, 5/13). High-frequency microsatellite instability tumours were preferentially located in the right colon and exhibited a higher frequency of loss of heterozygosity at the FHIT locus compared with low-frequency microsatellite instability and apparently stable cases (p=0.0243). Dukes' stage (p=0.0021), tumour localisation (p=0.0410) and pattern of cancer growth (p=0.0374), were the only factors affecting patient survival. However, a borderline improvement was noted in overall survival in high-frequency microsatellite instability and low-frequency microsatellite instability cancer patients (p=0.062).

CONCLUSIONS

These results indicate that low-frequency microsatellite instability tumours have different genetics and histological features and suggest that they are a distinct group of colorectal cancers.

Microsatellite instability and immunostaining for MSH-2 and MLH-1 in cutaneous and internal tumors from patients with the Muir-Torre syndrome

BACKGROUND

Muir-Torre syndrome (MTS) is characterized by the co-existence of sebaceous gland tumors of the skin and internal malignancies. Currently, MTS is regarded as a variant of the hereditary non-polyposis colon cancer syndrome (HNPCC). Both MTS and HNPCC are secondary to germline mutations in DNA mismatch repair genes (mainly MSH-2 and MLH-1).

METHODS

Cutaneous (eight sebaceous adenomas, one sebaceous carcinoma and one keratoacanthoma) and internal tumors (four colonic adenocarcinomas, two endometrial carcinomas, two transitional cell carcinomas of renal pelvis and ureter, one adenocarcinoma of the small bowel, one ovarian carcinoma and one colonic tubular adenoma) were obtained from six patients with MTS and were subjected to microsatellite instability (MI) analysis, and to immunostaining for MLH-1 and MSH-2. MI was assessed by evaluating three (CA)n dinucleotide repeats (D2S123, D5S346, D17S250) and the mononucleotide tracts BAT 26 and BAT 25.

RESULTS

All cutaneous and internal tumors exhibited MI. An immunohistochemical concordance between all tumors within each single patient was obtained in five cases. In these five patients all tumors exhibited a lack of MSH-2 staining, consistent with a germline abnormality in this gene. In the one remaining case, the immunohistochemical staining in the sebaceous adenoma was negative for MLH-1 and positive for MSH-2, consistent with a germline alteration in MLH-1. However, the colonic adenocarcinoma in that patient showed positivity for MSH-2 and an equivocal positivity for MLH-1.

CONCLUSIONS

The results confirm that tumors from patients with MTS exhibit MI. Moreover, immunostaining for MLH-1 and MSH-2 may be useful to identify the most probable gene responsible for the disease in each family.

Mutations in APC, Kirsten-ras, and p53--alternative genetic pathways to colorectal cancer

Colorectal cancer is one of the most significant causes of cancer death. A genetic model for colorectal cancer has been proposed in which the sequential accumulation of mutations in specific genes, including adenomatous polyposis coli (APC), Kirsten-ras (K-ras), and p53, drives the transition from healthy colonic epithelia through increasingly dysplastic adenoma to colorectal cancer. We have characterized tumor mutation spectra in a large cohort of colorectal cancer patients. In marked contrast to the predictions of the sequential model of mutation accumulation, only 6.6% of tumors were found to contain mutations in APC, K-ras, and p53, with 38.7% of tumors containing mutations in only one of these genes. The most common combination of mutations was p53 and APC (27.1%), whereas mutations in both p53 and K-ras were extremely rare. Statistical analysis (two-sided Fisher's exact test) confirmed that mutations in K-ras and p53 co-occurred less frequently than expected by chance (P < 0.01, Fisher's exact test). This finding suggests that these mutations lie on alternate pathways of colorectal tumor development. The heterogeneous pattern of tumor mutations in our patient cohort suggests that multiple alternative genetic pathways to colorectal cancer exist and that the widely accepted genetic model of cancer development is not representative of the majority of colorectal tumors.

Hereditary colorectal cancer: keeping it in the family--the bowel cancer story

Up to 20% of colorectal cancers are thought to have a genetic component. Several familial syndromes are known to confer an increased risk for colorectal cancer. Advances in our understanding of these syndromes has improved the care delivered to, and the overall survival of, these patients. Genetic testing has great potential to further improve detection and direct subsequent preventative measures. The diagnosis, management and surveillance issues relating to some of the more commonly encountered syndromes - in particular Familial Adenomatous Polyposis and Hereditary Non-Polyposis Colorectal Cancer - are reviewed.

Prognosis and response to therapy in colorectal cancer

Colorectal cancer is Europe's second biggest cancer killer. Yet despite advances in knowledge and changes in chemotherapy practice, we have not seen great strides in improved survival. Histopathological staging is at present the most accurate prognostic factor for survival and recurrence. Improvements in staging have led to the recognition of the importance of the circumferential resection margin (CRM) and how the quality of surgery influences local recurrence rates. Further refinements in staging and increasing knowledge of tumour biology will have a large contribution to play in the future.

Is reduced expression of mismatch repair genes MLH1 and MSH2 in patients with sporadic colorectal cancer related to their prognosis?

The majority of mutations in hereditary nonpolyposis colon carcinoma (HNPCC) patients affect the mismatch-repair genes (MMRG) MLHI and MSH2. In addition, mutations of these genes were found in about 15% of sporadic colorectal carcinomas which appear to be related to microsatellite instability (MSI). However, mutations in MMRG were not found in all MSI-positive carcinomas, but MMRG mutations may be relevant for the assessment of tumor characteristics and patients' prognosis. Therefore, we investigated the relationship between expression of MMRG, tumor biology and patients' survival. In 127 patients with sporadic colorectal carcinomas and a minimum of 5 years follow-up after curative surgery immunohistochemical detection of MLHI and MSH2 was analyzed semiquantitatively. Lost expression of MLHI has been found in tumor specimens from 10 patients, whereas MSH2 expression was missing in 5 patients. This reduced expression did not correlate with tumor stage, lymph node involvement, grading or tumor invasion into blood vessels. However, a significant correlation was found for lymphovascular invasion (P = 0.02) and localization within the colorectum (P = 0.003) in MLH1-negative carcinomas. In addition, although there was a clear tendency for longer overall survival (72 vs. 63 months) for patients with MLH1-negative carcinomas, significant differences for overall and recurrence-free survival were not seen. In conclusion of our results and a critical review of literature, the prognostic importance of the MMR genes in sporadic colorectal carcinomas remains controversial.

Loss of DNA mismatch repair proteins in skin tumors from patients with Muir-Torre syndrome and MSH2 or MLH1 germline mutations: establishment of immunohistochemical analysis as a screening test

Muir-Torre syndrome (MTS) is a rare autosomal-dominant disorder characterized by the predisposition to both sebaceous skin tumors (or multiple keratoacanthomas) and internal malignancies. A subtype of MTS is allelic to hereditary nonpolyposis colorectal cancer and is caused by germline mutations in the DNA mismatch repair genes MSH2 or MLH1. In these cases both internal and skin tumors show characteristic microsatellite instability (MSI). The aim of the present study was to determine whether immunohistochemical examination of MSH2 or MLH1 protein expression in MTS-associated skin tumors can be used as a diagnostic screening tool to identify patients with germline mutations in MSH2 or MLH1. In the present study 28 skin lesions from 17 patients (20 sebaceous gland tumors, 4 sebaceous hyperplasias, 3 keratoacanthomas, and 1 squamous cell carcinoma) were tested immunohistochemically with antibodies against MSH2 and MLH1. Eighteen of these tumors were from eight patients with known MSH2 germline mutations, two tumors were from a patient with a germline mutation in MLH1, and eight microsatellite stable sporadic skin tumors served as controls. One sample had to be excluded because of a lack of immunoreactivity. All eight microsatellite stable tumors expressed both DNA repair proteins. In 15 of the tumors from MSH2 germline mutation carriers, loss of MSH2 expression was observed, one tumor showed reduced MSH2 expression, and one tumor displayed positive immunoreactivity to MSH2. Both tumors of the MLH1 germline mutation carrier showed loss of the MLH1 protein. In conclusion, our findings demonstrate that immunohistochemical testing of MTS-related skin tumors is a reliable screening method with high predictive value for the diagnosis of the DNA mismatch repair-deficient MTS.

Immunohistochemistry versus microsatellite instability testing in phenotyping colorectal tumors

PURPOSE

To compare microsatellite instability (MSI) testing with immunohistochemical (IHC) detection of hMLH1 and hMSH2 in colorectal cancer.

PATIENTS AND METHODS

Colorectal cancers from 1,144 patients were assessed for DNA mismatch repair deficiency by two methods: MSI testing and IHC detection of hMLH1 and hMSH2 gene products. High-frequency MSI (MSI-H) was defined as more than 30% instability of at least five markers; low-level MSI (MSI-L) was defined as 1% to 29% of loci unstable.

RESULTS

Of 1,144 tumors tested, 818 showed intact expression of hMLH1 and hMSH2. Of these, 680 were microsatellite stable (MSS), 27 were MSI-H, and 111 were MSI-L. In all, 228 tumors showed absence of hMLH1 expression and 98 showed absence of hMSH2 expression: all were MSI-H.

CONCLUSION

IHC in colorectal tumors for protein products hMLH1 and hMSH2 provides a rapid, cost-effective, sensitive (92.3%), and extremely specific (100%) method for screening for DNA mismatch repair defects. The predictive value of normal IHC for an MSS/MSI-L phenotype was 96.7%, and the predictive value of abnormal IHC was 100% for an MSI-H phenotype. Testing strategies must take into account acceptability of missing some cases of MSI-H tumors if only IHC is performed.

Involvement of hMSH6 in the development of hereditary and sporadic colorectal cancer revealed by immunostaining is based on germline mutations, but rarely on somatic inactivation

Germline mutations in human mismatch repair (MMR) genes yield a predisposition for the hereditary nonpolyposis colon cancer (HNPCC) syndrome. In contrast to hMLH1 and hMSH2, little is known about the overall involvement of hMSH6 in colorectal cancer. We investigated 82 tumors from patients who fulfilled the Bethesda guidelines for HNPCC as well as 146 sporadic tumors, analyzing microsatellite instability and expression of the 4 MMR proteins hMSH6, hMSH2, hMLH1 and hPMS2. Four tumors with lost expression and 1 tumor with cytoplasmic expression of hMSH6 were identified. Sequence analysis revealed germline mutations in 4 of the 5 patients, including 1 patient with sporadic disease. The lost or reduced expression of hMSH2 and hMLH1 was always identical to its heterodimerization partners, hMSH6 and hPMS2, respectively. Furthermore, hMSH2 expression was reduced upon hMSH6 deficiency. Abnormal expression of 1 or more of the 4 proteins was always associated with a high level of microsatellite instability (MSI-H). Conversely, all but 1 of the 44 MSI-H tumors had abnormal expression of 1 or more of the proteins, basically excluding additional genes associated with the MSI-H phenotype. We conclude that the involvement of somatic or epigenetic hMSH6 inactivation in colorectal cancer is rare.

Frequency of hereditary non-polyposis colorectal cancer in Danish colorectal cancer patients

BACKGROUND

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominant cancer syndrome, characterised by familial aggregation of HNPCC related cancers, germline mutations in mismatch repair genes, and/or microsatellite instability (MSI) in tumour tissue.

AIM

To estimate the frequency of HNPCC among non-selected Danish patients with colorectal cancer (CRC), and to evaluate the value of MSI analysis as a pre-screen test.

METHODS

This was a prospective population based study on consecutive CRC patients. A family history of malignancy was obtained and suspected HNPCC cases were screened for hMLH1/hMSH2 mutations and subjected to MSI analysis. Patients with germline mutations and/or those with Amsterdam criteria I or II families were categorised as HNPCC patients.

RESULTS

Among 1328 eligible CRC patients, 1200 (90.4%) completed a questionnaire. A total of 1.7% (95% confidence interval (CI) 1.0-2.4) (20 cases) were categorised as HNPCC patients. Amsterdam criteria I or II were met in 18 cases (1.5%), and in another two cases (0.2%) pathogenic hMLH1/hMSH2 mutations were detected without fulfillment of the Amsterdam criteria I or II. Among 77 patients younger than 50 years of age, 11 cases (14.3%) were categorised as HNPCC. The Amsterdam criteria I or II were met in eight of 10 gene carriers (80%). The MSI-high phenotype was demonstrated in all 10 gene carriers.

CONCLUSION

The frequency of HNPCC was approximately 1.7% among all CRC cases and 14.3% among patients younger than 50 years of age. MSI analysis is a reliable pre-screen test for hMLH1/hMSH2 mutations in families suspected of having HNPCC.

Clinicopathological and molecular genetic analysis of 4 typical Chinese HNPCC families

AIM: To study the clinicopathological and mole cular genetic characteristics of typical Chinese hereditary nonpolyposis cotorectal cancer (HNPCC) families.

METHODS: Four typical Chinese HNPCC families were analyzed using microdissection, microsatellite instability analysis, immunostaining of hMSH2 and hMLH1 proteins and direct DNA sequencing of hMSH2 and hMLH1 genes.

RESULTS: All five tumor tissues of 4 probands from the 4 typical Chinese HNPCC families showed microsatellite instability at more than two loci (MSI-H or RER+ phenotype). Three out of the 4 cases lost hMSH2 protein expression and the other case showed no hMLH1 protein expression. Three pathological germline mutations (2 in hMSH2 and 1 in hMLH1), which had not been reported previously, were identified. The same mutations were also found in other affected members of two HNPCC families, respectively.

CONCLUSION: Typical Chinese HNPCC families showed relatively frequent germline mutation of mismatch repair genes. High-level microsatellite instability and loss of expression of mismatch repair genes correlated closely with germline mutation of mismatch repair genes. Microsatellite instability analysis and immunostaining of mismatch repair gene might serve as effective screening methods before direct DNA sequencing. It is necessary to establish clinical criteria and molecular diagnostic strategies more suitable for Chinese HNPCC families.

MLH1 and MSH2 protein immunohistochemistry is useful for detection of hereditary non-polyposis colorectal cancer in young patients

AIMS

Hereditary non-polyposis colorectal cancer is related to germline mutations of DNA mismatch repair genes MLH1 and MSH2, which result in microsatellite instability and loss of protein expression of the corresponding mutated gene in the tumour tissue.

METHODS AND RESULTS

MLH1 and MSH2 protein expression was studied by immunohistochemistry in paraffin-embedded surgical samples of 100 colorectal adenocarcinomas occurring before 50 years of age. Absence of tumour cell nuclear staining with positive internal control (normal mucosa, lymphoid follicles) was considered negative. Loss of MLH1 or MSH2 expression was found in 20 cases with microsatellite instability in 15 cases. Twelve of these patients had a family history of colorectal cancer. Compared with MLH1- and MSH2-positive cases, MLH1- or MSH2-deficient colorectal adenocarcinomas were significantly associated on multivariate analysis with a younger age (38 vs. 43 years, P;0.0224), a larger tumour size (60 +/- 6 vs. 46 +/- 2 mm, P=0.0291), an expanding margin (85% vs. 51%, P=0.0159), a higher number of tumour-infiltrating lymphocytes assessed by CD3 immunostaining (202 +/- 48 vs. 33 +/- 4 CD3+ lymphocytes/10 high-power fields, P=0.0039), and a grade 2 Crohn's like lymphoid reaction (70% vs. 9%, P=0.0037). The two groups were not different for tumour site, differentiation, pTNM stage, vascular and perineural invasion, peripheral adenomatous residue, and 5-year survival rates.

CONCLUSIONS

MLH1- or MSH2-deficient colorectal carcinomas of young patients exhibit pathological and molecular features similar to hereditary non-polyposis colorectal cancer. This suggests that MLH1 and MSH2 immunohistochemistry is valuable for detecting hereditary non-polyposis colorectal cancer in young patients.

Recent pathology related advances in colorectal adenocarcinomas

This brief review addresses some new developments in the understanding of the molecular pathogenesis of colorectal cancer, including the mismatch repair protein mechanism of colorectal adenocarcinoma carcinogenesis. The second part of this review summarizes recent improvements in the pathological evaluation of colorectal resection specimens, and highlights the advantage seen in the resulting improved quality of gross dissection provided by the use of highly trained non-medical pathology assistants. Topics also covered include optimum methods of assessment of radial resection margins, the accuracy of measured margin distances, the assessment of adenocarcinoma involvement of the peritoneal serosal surface, improved methods of lymph-node recovery from colorectal adenocarcinoma resection specimens and the recently recognized adverse prognostic significance of extranodal pericolonic tumour deposits. Formats for standardized reporting of colorectal resection specimens are presented as a means to improve quality and consistency of pathological data recording and collection.

Microsatellite instability and the clinicopathological features of sporadic colorectal cancer

BACKGROUND AND AIMS

In this study, we prospectively examined the clinical significance of the microsatellite instability (MSI) phenotype in sporadic colorectal cancer, and investigated methods for effective identification of these tumours in routine pathology practice.

METHODS

DNA was extracted from 310 tumours collected from 302 consecutive individuals undergoing curative surgery for sporadic colorectal cancer. Microsatellite status was determined by polymerase chain reaction amplification using standard markers, while immunostaining was used to examine expression of MLH1, MSH2, and p53.

RESULTS

Eleven per cent of tumours showed high level instability (MSI-H), 6.8% had low level instability (MSI-L), and the remainder were stable. MSI-H tumours were significantly more likely to be of high histopathological grade, have a mucinous phenotype, and to harbour increased numbers of intraepithelial lymphocytes. They were also more likely to be right sided, occur in women, and be associated with improved overall survival. In total, 25 (8%) tumours showed loss of staining for MLH1 and a further three tumours showed absence of staining for MSH2. The positive and negative predictive value of immunohistochemistry in the detection of MSI-H tumours was greater than 95%.

CONCLUSIONS

We conclude that the MSI-H phenotype constitutes a pathologically and clinically distinct subtype of sporadic colorectal cancer. Immunohistochemical staining for MLH1 and MSH2 represents an inexpensive and accurate means of identifying such tumours.

Diagnosis of microsatellite instability-positive colorectal cancer

The continuing increase in knowledge regarding the genetic basis of carcinogenesis has led to diverse efforts to exploit this knowledge clinically, primarily in the form of predictive genetic testing. In conjunction with family history, gene tests are intended to improve individual cancer risk assessment. At present, genetic testing for colorectal cancer (CRC) risk--in the form of microsatellite instability (MSI) screening and DNA sequencing--is applied in hereditary nonpolyposis colorectal cancer (HNPCC). In this inherited colorectal tumor syndrome, determining the genetic status may result in an individually tailored surveillance program and prophylactic treatment, reducing cancer morbidity and mortality.

MLH1 and MSH2 protein expression as a pre-screening marker in hereditary and non-hereditary endometrial hyperplasia and cancer

The predictive value of MLH1 or MSH2 protein expression for the presence of truncating germline mutations was examined in benign and (pre)malignant endometrial samples from 3 patient groups: (I) 10 endometrial cancer patients from hereditary non-polyposis colorectal cancer (HNPCC) families with (n = 6) or without (n = 4) a known germline mutation; (II) 15 women from HNPCC families with (n = 7) or without (n = 8) a known germline mutation, who underwent endometrial sampling for non-malignant reasons; (III) 38 endometrial cancer patients <50 years of age, without HNPCC family history. Immunostaining for MLH1 and MSH2 was performed on paraffin-embedded sections. In group III, tumor DNA was examined for microsatellite instability (MSI) and MLH1, MSH2 and MSH6 mutation analysis was carried out. In 6/6 MLH1/MSH2 mutation carriers with endometrial cancer (group I), concordance was found between protein loss in the tumor and the corresponding mutation. In 3 MLH1 mutation carriers, MLH1 protein loss was also observed in concurrent endometrial hyperplasia. In group II, no protein loss was detected in normal endometrial tissue samples; in 3/4 patients with endometrial hyperplasia, MLH1/MSH2 protein loss was observed. In group III, protein loss was detected in 12/38 patients (9 MLH1, 3 MSH2), while in 3/11 patients with concurrent endometrial hyperplasia protein loss was also observed in the hyperplasia. MSI analysis in group III revealed 26 MSI-low and 12 MSI-high tumors. Mutation analysis in 28/38 patients showed only 1 missense MSH6 and no MLH1 or MSH2 germline mutations. In group III, loss of MLH1/MSH2 protein expression was not related to the presence of MSI or MLH1/MSH2 germline mutations. In conclusion, MLH1 or MSH2 protein loss in HNPCC-related endometrial neoplasia is strongly related to corresponding germline mutations. This relation was not clearly present in young sporadic endometrial cancer patients. Immunohistochemical pre-screening of the MLH1 and MSH2 proteins in endometrial hyperplasia or cancer can thus be helpful in HNPCC families. Frequent loss of MLH1 or MSH2 protein in endometrial hyperplasia indicates that this loss is an early event in endometrial carcinogenesis.

Colonic screening and surveillance

Screening for colorectal cancer has not obtained worldwide acceptance in spite of its proven survival benefit for average-risk persons and some high-risk groups. The incidence of and mortality from colorectal cancer are worrying in Europe as well as in the USA, Australia and Japan. The best evidence-based studies are those published on screening using faecal occult blood tests, endoscopic methods and different tumour markers having been evaluated to a lesser degree. Feasibility studies are necessary before massive screening can be undertaken because the results obtained from randomized studies may not be reproduced to a satisfactory degree in average- as well as high-risk populations. Primary prevention by dietary intervention and drugs has been studied in great detail, so far without any major breakthrough. This chapter will address different screening methods in populations with a varying risk of colorectal cancer, together with providing a short review of prevention and intervention strategies.

Role of molecular diagnostic testing in familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer families

PURPOSE

Genetic tests are available for familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer. The goal of this review was to develop an algorithm for application of molecular diagnostic techniques to the management of hereditary colorectal carcinoma and to familiarize the clinician with the vocabulary of molecular genetic testing for hereditary colorectal carcinoma.

METHODS

Studies examining the clinical use of genetic testing for hereditary colorectal carcinoma syndromes are evaluated. Recent advances in molecular genetic technology are reviewed, and clinical management as practiced here and elsewhere is outlined.

RESULTS

This review is a guide to the most reliable molecular diagnostic techniques. Three key questions are answered: who, when, and how to test.

CONCLUSIONS

When integrated with existing testing protocols for colorectal carcinoma and when applied with appropriate caveats, particularly regarding interpretation of negative results, genetic testing can result in improved management of patients and families.

Histopathological identification of colon cancer with microsatellite instability

Cancer with high levels of microsatellite instability (MSI-H) is the hallmark of hereditary nonpolyposis colorectal cancer syndrome, and MSI-H occurs in approximately 15% of sporadic colorectal carcinomas that have improved prognosis. We examined the utility of histopathology for the identification of MSI-H cancers by evaluating the features of 323 sporadic carcinomas using specified criteria and comparing the results to MSI-H status. Coded hematoxylin and eosin sections were evaluated for tumor features (signet ring cells; mucinous histology; cribriforming, poor differentiation, and medullary-type pattern; sponge-like mucinous growth; pushing invasive margin) and features of host immune response (Crohn's-like lymphoid reaction, intratumoral lymphocytic infiltrate, and intraepithelial T cells by immunohistochemistry for CD3 with morphometry). Interobserver variation among five pathologists was determined. Subjective interpretation of histopathology as an indication for MSI testing was recorded. We found that medullary carcinoma, intraepithelial lymphocytosis, and poor differentiation were the best discriminators between MSI-H and microsatellite-stable cancers (odds ratio: 37.8, 9.8, and 4.0, respectively; P = 0.000003 to < 0.000001) with high specificity (99 to 87%). The sensitivities, however, were very low (14 to 38%), and interobserver agreement was good only for evaluation of poor differentiation (kappa, 0.69). Mucinous histopathological type and presence of signet ring cells had low odds ratios of 3.3 and 2.7 (P = 0.005 and P = 0.02) with specificities of 95% but sensitivities of only 15 and 13%. Subjective interpretation of the overall histopathology as suggesting MSI-H performed better than any individual feature; the odds ratio was 7.5 (P < 0.000001) with sensitivity of 49%, specificity of 89%, and moderate interobserver agreement (kappa, 0.52). Forty intraepithelial CD3-positive lymphocytes/0.94 mm2, as established by receiver operating characteristic curve analysis, resulted in an odds ratio of 6.0 (P < 0.000001) with sensitivity of 75% and specificity of 67%. Our findings indicate that histopathological evaluation can be used to prioritize sporadic colon cancers for MSI studies, but morphological prediction of MSI-H has low sensitivity, requiring molecular analysis for therapeutic decisions.

Efficient detection of hereditary nonpolyposis colorectal cancer gene carriers by screening for tumor microsatellite instability before germline genetic testing

BACKGROUND & AIMS

The optimal strategy for the detection of hereditary nonpolyposis colorectal cancer (HNPCC) gene carriers remains uncertain. We evaluated whether microsatellite instability (MSI) analysis or MSH2 and MLH1 protein immunostaining of tumors will screen individuals efficiently for germline MSH2 and MLH1 testing.

METHODS

We performed a case-series study of 114 eligible families enrolled in our high-risk colorectal cancer (CRC) registry. Medical history data were collected on probands and relatives. MSI analysis was performed on proband tumors, and MSH2 and MLH1 protein immunostaining was assessed. Denaturing gradient gel electrophoresis was used to identify germline MSH2 or MLH1 mutations in probands found to have tumors with high-frequency MSI.

RESULTS

Tumor tissue and adequate clinical data were available in 109 of the 114 families. Amsterdam criteria and Bethesda guidelines were met by 23% and 70% of the families, respectively. High-frequency MSI was identified in the proband tumors in 47 of the 109 families (43%). Germline MSH2 and MLH1 gene testing was carried out in the probands of 32 of 47 families with MSI-H tumors. Mutations were detected in 16 families (9 in MSH2 and 7 in MLH1) and sequence variants of uncertain significance in 5 families (1 in MSH2 and 4 in MLH1). Germline mutations or sequence variants of uncertain significance were detected in 15 of 19 (79%) of our Amsterdam families and in 6 of 13 (46%) of our non-Amsterdam families with MSI-H tumors. MSH2 and MLH1 protein immunostaining was assessed in 38 of the 47 MSI-H tumors. Unequivocal loss of hMLH1 expression was found in 20 tumors and loss of MSH2 expression in 9 tumors. Corresponding loss of protein expression was seen in 17 of 18 (94%) of tumors from probands with germline mutations or variants.

CONCLUSIONS

The detection of high-frequency MSI or the loss of MSH2 or MLH1 immunostaining in CRCs are both useful criteria for selecting high-risk patients who should be tested for germline mutations in MSH2 or MLH1.

Sporadic colorectal adenocarcinomas with high-frequency microsatellite instability

BACKGROUND

Widespread microsatellite instability (MSI) occurs in nearly 15% of sporadic colorectal cancers. Large bowel carcinomas with high-frequency MSI (MSI-H) (instability at > or = 30% of microsatellite loci) are believed to display distinctive pathologic features and to behave less aggressively than microsatellite-stable (MSS) tumors and carcinomas with low-frequency MSI (MSI-L) (instability at < 30% of microsatellite loci). The aim of the current study was to accurately define the clinicopathologic and biologic features of MSI-H sporadic colorectal carcinomas.

METHODS

MSI status was evaluated in 216 large bowel adenocarcinomas using polymerase chain reaction (PCR) and 6 microsatellite markers. Tumors that showed instability with at least two microsatellite markers were classified as MSI-H, whereas the other tumors were classified as MSI-L (instability at one locus) or MSS (no instability). Expression of p53, hMLH1, and hMSH2 gene products was determined by immunohistochemistry, and DNA ploidy pattern was determined by flow cytometry. The prognostic significance of MSI status was assessed by univariate and multivariate survival analyses.

RESULTS

The significantly different pathologic features of MSI-H carcinomas were proximal location; large size; mucinous and medullary histotype; poor differentiation; expanding pattern of growth; more frequent Crohn-like conspicuous lymphoid reaction; and low incidence of extramural vein invasion. Most MSI-H tumors were DNA diploid (33 of 40 tumors; 82.5%) and p53 negative (34 of 44 tumors; 77.3%). Conversely, DNA aneuploidy and p53 overexpression were observed in 82.3% (130 of 158 tumors; P < 0.0001) and 54.1% (93 of 172 tumors; P = 0.0002) of MSI-L/MSS tumors, respectively. Loss of hMLH1 or hMSH2 expression was detected in a high fraction of MSI-H carcinomas (86. 0%). Patients with MSI-H tumors showed a better clinical outcome than patients with MSI-L/MSS tumors (P = 0.0017). Furthermore, in multivariate analysis that included conventional clinicopathologic parameters, MSI status, and p53 expression as covariates, MSI status was a significant independent prognostic indicator of disease specific survival.

CONCLUSIONS

Assessment of MSI status is an essential step in the genetic characterization of large bowel carcinomas and identifies a subset of tumors with distinct clinical, pathologic, and biologic features.

Familial colorectal cancer: pathology and molecular characteristics

Appropriate management of familial colorectal cancer revolves around the diagnosis of the underlying genetic syndrome. This necessitates an interdisciplinary approach allowing integration of clinical, morphological, and molecular evidence that may involve several members of the same family. Genetic disorders express themselves over time, whereas clinical investigation of family members is likely to be episodic. Generic features of hereditary colorectal cancer syndromes include a positive family history, early age at onset, multiple neoplasms, and extracolonic lesions of either a developmental or neoplastic nature. Deriving a complete description of a genetic disorder is hampered by the need to trace and obtain tissue samples from many institutions. This review examines the usefulness of tissue-based investigations, both morphological and molecular, in raising the suspicion of familial colorectal cancer, providing a definitive tissue diagnosis and contributing to the larger body of diagnostic evidence. The account focuses on the two most well-studied syndromes--familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC)--but consideration is also given to less well-understood syndromes. Some of these, notably hyperplastic polyposis and mixed polyposis, may closely mimic FAP or HNPCC.

Hereditary non-polyposis colorectal cancer: an updated review

INTRODUCTION

Colorectal cancer is the commonest cause of death due to malignancy in non-smokers in the western countries. The two main hereditary types of colorectal cancer are familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC), constituting approximately 10% of all cases of colorectal cancer. The main aim of this review is to reappraise the current advances in the genetics and diagnosis of HNPCC.

METHODS

A Medline search was carried out to identify papers published from 1970 to 1999 on HNPCC. Embase and Cochrane databases were also searched. Reference lists of retrieved articles were carefully searched for additional articles.

RESULTS AND CONCLUSIONS

Recent technological advances in the genetics of HNPCC have refined the criteria for diagnosis and management of HNPCC, however current policies regarding the testing of pedigrees are not clearly established. We believe that with the rapid development in this area definitive clinical guidelines will need to be available in future for the management of HNPCC.

Detection of somatic DNA alterations in azoxymethane-induced F344 rat colon tumors by random amplified polymorphic DNA analysis

Colon carcinogenesis induced in rats by azoxymethane (AOM) is a useful experimental model as it mimics the human adenoma-carcinoma sequence and allows the study of dietary variation and of the effects of chemopreventive substances. Alterations of specific oncogenes and tumor suppressor genes (APC and K-ras) play roles at different stages of this carcinogenesis process. Recently, it has been suggested that genomic instability is the necessary step for the generation of multiple mutations underlying the occurrence of cancer. We studied the frequency of K-ras and microsatellite instability (MSI) in 30 colorectal tumors induced by AOM (30 mg/kg) in F344 rats. We also used the random amplified polymorphic DNA (RAPD) method to identify genomic alterations in chemically induced aberrant crypt foci (ACF), adenomas and adenocarcinomas. K-ras mutations were identified in 16.7% of the cases (5/30; 9% in adenomas and 37.5% in adenocarcinomas) and MSI in 20% (6/30) of the tumors (only one sample exhibited instability at more than one locus). Of 21 primers used for the RAPD assay, six were very informative. All the analyzed tumors (16/16) showed at least one RAPD profile with lost or additional bands compared with the normal mucosa. A lower level of genomic alteration was present in the ACF analyzed (7/10). In conclusion, K-ras and MSI are not often involved in the AOM carcinogenesis in the rat, whereas extensive genomic instability is always present and can be detected using the RAPD analysis.

Evaluation of colonoscopic sized biopsies for microsatellite instability and adenomatous polyposis coli (APC) variants

OBJECTIVE

Knowledge of certain genetic changes associated with the development of colorectal cancer may influence surgical treatment in the future. Cancers are known to show intratumoural genetic heterogeneity. The aim of this study was to determine whether colonoscopic sized biopsies provide enough tissue to overcome the effects of tumour heterogeneity for the results of genetic analysis to be representative of the tumour as a whole.

PATIENTS AND METHODS

Using colonoscopic biopsy forceps, samples were taken from 30 resected colorectal cancers and investigated for microsatellite instability (MSI) at five loci and changes in the adenomatous polyposis coli gene (APC) by single-stranded conformational polymorphism analysis. Identical genetic analysis was carried out on larger specimens taken from each of these cancers to determine whether the molecular findings from the large specimen were the same as those from colonoscopic sized biopsies.

RESULTS

The microsatellite instability and APC status of the colonoscopic sized biopsies and those from larger specimens were completely consistent.

CONCLUSION

These results suggest that colonoscopic sized biopsies are reliable in determining the MSI status and APC variants of individual colorectal cancers.

Genetic testing

New research developments in the molecular genetics of cancer have led to the feasibility of cancer genetic testing. At present, genetic test results can better inform individuals at risk about appropriately tailored strategies for cancer screening and prevention. In the future, more persons will be eligible for genetic evaluation; in particular, if it is shown that patients with cancer who are carriers of germline mutations respond differently to treatments, genetic testing may be warranted. Consideration needs to be given to the appropriate delivery of genetic risk assessment and testing. There is a great potential for misinterpretation of gene test results and for adverse psychosocial consequences for patients. Genetic counseling is an important component in cancer risk assessment and management, particularly in helping persons at risk understand the implications of gene test results in the context of their experience with cancer and surveillance.

DNA microsatellite instability and mismatch repair protein loss in adenomas presenting in hereditary non-polyposis colorectal cancer

BACKGROUND AND AIM

Hereditary non-polyposis colorectal cancer (HNPCC), as its name implies, is associated with few adenomas, and the early evolution of colorectal neoplasia is poorly understood. In this study our aim was to clarify the genetic profiles of benign polyps in subjects with HNPCC using a combined molecular and immunohistochemical approach.

METHODS

Thirty adenomas and 17 hyperplastic polyps were obtained from 24 affected HNPCC subjects. DNA was extracted from paraffin embedded tissue by microdissection and analysed for the presence of microsatellite instability (MSI) and mutations in five genes known to be targets in mismatch repair deficiency (TGFbetaRII, IGF2R, BAX, hMSH3, and hMSH6). Serial sections were stained by immunohistochemistry for hMLH1 and hMSH2.

RESULTS

Twenty four (80%) of 30 adenomas showed MSI. Of MSI positive adenomas, 66.7% showed MSI at more than 40% of markers (high level of MSI (MSI-H)). Two of 17 hyperplastic polyps revealed MSI at one marker (low level of MSI (MSI-L)). A significant association was found between MSI-H and high grade dysplasia in adenomas (p=0.004). Eight of nine adenomas with mutations of coding sequences revealed high grade dysplasia and all nine were MSI-H. Four of the nine ranged in size from 2 to 5 mm. The presence of the hMSH6 mutation was significantly correlated with high levels of MSI (80% of markers) (p<0.02). Twenty four adenomas gave evaluable results with immunohistochemistry. One of six (17%) microsatellite stable, six of seven (86%) MSI-L, and 11 of 11 (100%) MSI-H adenomas showed loss of either hMLH1 or hMSH2.

CONCLUSIONS

Most adenomas in subjects with a definite diagnosis of HNPCC show MSI (80%). The finding of MSI-L is usually associated with loss of expression of hMLH1 or hMSH2, unlike the situation in MSI-L sporadic colorectal cancer. The transition from MSI-L to MSI-H correlated with the finding of high grade dysplasia and mutation of coding sequences and may be driven by mutation of secondary mutators such as hMSH3 and hMSH6. Advanced genetic changes may be present in adenomas of minute size.

Pathology of hereditary nonpolyposis colorectal cancer

The magnitude of the pathologist's role in the diagnosis of hereditary nonpolyposis colorectal cancer (HNPCC) is underestimated. The diagnostic features are not specific to HNPCC cancers, but relate to all cancers showing high levels of DNA microsatellite instability (MSI-H). Three major groups of MSI-H cancers can be recognized by histopathological criteria: (1) right-sided poorly differentiated cancers, (2) right-sided mucinous cancers, and (3) adenocarcinomas in any location showing tumor-infiltrating (intraepithelial) lymphocytes (TIL). The poorly differentiated cancers are relatively well circumscribed and the cells are arranged in sheets or trabeculae. TIL may be very numerous in poorly differentiated cancers. The presence of TIL as estimated in H&E sections equates with a percentage of intraepithelial T cells (CD3+) in the range of 4 to 30%. Most of the T cells are CD8+ (cytotoxic T cells). Peritumoral lymphocytes and the so-called Crohn's-like reaction are associated with TIL, but are harder to quantify. Of the 15% of colorectal cancers that are MSI-H, 13% will be sporadic and 2% will occur in the context of HNPCC. HNPCC should be suspected if the patient is young (less than 55 years) because sporadic MSI-H cancers (associated with hypermethylation of the promoter region of hMLH1) occur almost exclusively in elderly subjects. Workup of a suspected case should include DNA microsatellite testing with a panel of mononucleotide (e.g., BAT26, BAT25) and dinucleotide (e.g., D5S346, D2S123, and D177S250) markers before referral to a cancer family or clinical genetics clinic. Immunohistochemical staining for hMLH1 and hMSH2 identifies the underlying mutation in a proportion of cases. The colorectal adenoma is the usual precursor lesion in HNPCC, though serrated polyps are implicated in a small subset.

ACP Best practice no 159. Examination of large intestine resection specimens

Macroscopic examination of large intestinal resection specimens by the surgical pathologist provides important diagnostic and prognostic information. This review summarises current recommended protocols and evidence based guidelines for gross description, dissection, and histological block selection in both neoplastic and non-neoplastic colorectal disease. Specific lesions discussed include colorectal cancer, polypectomies and polyposis syndromes, and inflammatory bowel disease. Microscopic examination is briefly described, with emphasis on certain pitfalls that might be encountered in routine practice. A section covering special techniques for the investigation of occult bleeding is included.

Defective hMSH2/hMLH1 protein expression is seen infrequently in ulcerative colitis associated colorectal cancers

BACKGROUND

Ulcerative colitis is associated with an increased risk of colorectal cancer above that of the normal population. The relative risk correlates with the extent and duration of the disease but the genetic basis of ulcerative colitis associated cancer risk is not known.

AIMS

To assess the prevalence of microsatellite instability and mismatch repair gene abnormalities in ulcerative colitis associated colorectal cancer.

PATIENTS

Forty six patients with colorectal cancer, with a previous histological diagnosis of ulcerative colitis.

METHODS

The frequency of microsatellite instability and/or immunohistochemical expression of hMSH2 and hMLH1 was assessed. Thirty three cases were investigated using both approaches.

RESULTS

Although 6/41 (14.6%) cases showed microsatellite instability at one or more markers, only one case (2. 4%) exhibited high level instability (at least two markers affected). Of 38 cases which were assessed using antibodies against hMSH2 and hMLH1, only one case (2.6%) showed loss of expression. This case, which showed loss of hMSH2 expression, was the same case which exhibited high level microsatellite instability. The 33 cases which were investigated using both approaches showed that loss of expression of either hMSH2 or hMLH1 was not seen in any case which exhibited microsatellite instability in no more than one marker.

CONCLUSIONS

This study suggests that both high level microsatellite instability and loss of expression of hMSH2/hMLH1 are infrequent events in ulcerative colitis associated colorectal cancers. Low level microsatellite instability was not associated with loss of expression of either hMSH2 or hMLH1.