Sporadic colorectal adenocarcinomas with high-frequency microsatellite instability: Pathobiologic features, hMLH1 and hMSH2 expression, and clinical outcome

Lymph node counts, rates of positive lymph nodes, and patient survival for colon cancer surgery in Ontario, Canada: a population-based study

BACKGROUND AND OBJECTIVES

This study assessed lymph node counts, lymph node status (positive or negative), and survival among patients undergoing colon cancer surgery in Ontario, Canada.

METHODS

We obtained data from the Ontario Cancer Registry on 960 patients who underwent a major colon cancer resection in years 1991-1993. Patients and hospitals were ranked by lymph node count to correlate lymph node counts and lymph node status. For node-negative patients we assessed the influence of patient, hospital, and tumor factors on lymph node counts and survival.

RESULTS

The rate of node-positive patients was similar among the lymph node count groups. For example, the odds ratio of a patient being node positive if the lymph node count was 10-36 versus 1-3 was 1.0 (CI 0.6-1.6, P = 0.42). Among node-negative patients, survival was improved for patients with a high (10-36) versus low (1-3) lymph node count (HR 0.6, CI 0.4-1.0, P = 0.03). No patient, hospital, or tumor factors predicted both a higher lymph node count and improved survival.

CONCLUSIONS

In this population-based study of patients undergoing colon cancer surgery, higher lymph node counts did not correlate with increased rates of node-positive status.

Chromosomal aberrations and microsatellite instability of malignant peripheral nerve sheath tumors: a study of 10 tumors from nine patients

Malignant peripheral nerve sheath tumor (MPNST) is an uncommon soft tissue neoplasm with a poor prognosis, occurring sporadically or associated with neurofibromatosis type 1 (NF1); however, the histogenesis of MPNST remains unclear, especially in sporadic tumors. There are two major forms of genomic instability in human cancer: chromosomal instability (CIN) and microsatellite instability (MSI). An inverse relationship has recently been demonstrated between CIN and MSI in colorectal cancers. CIN and MSI are suggested to be individual pathways, which are involved in the pathogenesis and which may lead to specific clinical and pathological characteristics. To elucidate the chromosomal aberration as a consequence of CIN and MSI status of MPNST, we karyotyped 10 MPNSTs from nine patients, and examined the MSI of seven microsatellite markers using high-resolution fluorescence microsatellite analysis; 2 out of 10 cases (20%) had normal karyotypes, and 8 out of 10 cases (80%) revealed structural and numerical chromosomal aberrations. Three of the 10 cases (30%) showed near triploidy. The most frequent aberration was -22 (40%), followed by +2, +14, -13, -17, and -18 (30% each). An MSI-low status was observed in 30% of cases; the remaining cases showed microsatellite stability. These findings suggest that chromosomal aberration as a consequence of CIN has a greater role in the pathogenesis of MPNST than does that due to MSI.

Genomic instability and tissue expression of angiogenic growth factors in sporadic colorectal cancer

BACKGROUND

Chromosomal instability evidenced by a loss of heterozygosity (LOH) is implicated as a predictor of poor survival in patients with colorectal cancer, whereas microsatellite instability (MSI) is associated with improved survival rates. We investigated the relationship between tumor expression of angiogenic growth factors and genomic alterations in colorectal cancer.

METHODS

Two genotypes, LOH and MSI, determined by microsatellite markers in the 4 cancer-related chromosomes 2p, 3p, 17p, and 18q, were analyzed in 73 patients with colorectal cancer. The tumor-specific expression of vascular endothelial growth factor and hepatocyte growth factor (HGF) were quantified, and the interleukin-6 network also was evaluated.

RESULTS

MSI-positive neoplasms showed a lesser expression of both tumor growth factors and interleukin-6. In contrast, LOH-positive neoplasms showed a greater expression of HGF and a lesser expression of interleukin-1-receptor antagonist. MSI neoplasms were correlated with favorable prognosis in agreement with previous findings.

CONCLUSIONS

The suppressed production of angiogenic growth factors in MSI cancers partly might explain the better prognosis in MSI-positive patients. The interleukin-6 network, which upregulates production of vascular endothelial growth factor and HGF, might be involved in this mechanism.

Mucinous colorectal cancers with chromosomal instability: a biologically distinct and aggressive subtype

Colorectal cancers can progress through 2 pathways of genomic instability: microsatellite instability (MSI) and chromosomal instability (CSI). We investigated the influence of CSI and MSI on clinicopathological features and survival of 35 patients affected by mucinous colorectal cancers (MCRC). MSI status was determined by PCR amplification using 5 standard markers. Evidence for CSI was gathered by identifying loss of heterozygosity (LOH) of 4 loci (2p, 5q, 17p, 18q). We defined "MSI-MCRC" as those that showed MSI-H, and "CSI-MCRC" as those that showed LOH at 1 or more of these sites but did not show MSI-H. Among 35 cases, 18 cases (51.4%) were CSI-MCRC, whereas 11 cases (31.4%) were MSI-MCRC. Significant differences were found between CSI-MCRC and MSI-MCRC regarding the following clinicopathological features: tumor location (P=0.00026), lymph node metastasis (P=0.026), and TNM stage (P=0.026). Kaplan-Meier survival curves and log-rank analysis demonstrated that MSI-MCRC was associated with better prognosis than CSI-MCRC, although no significant difference was found (P=0.10). CSI-MCRC correlates more strongly with lymph node metastasis and advanced stage than MSI-MCRC. This indicates that CSI-MCRC is an aggressive subtype.

Relationship between genetic alterations and prognosis in sporadic colorectal cancer

Because chromosomal chromosomal instability (CIN) and microsatellite instability (MSI) are important genetic alterations in colorectal cancers, we classified the sporadic colorectal cancers (CRC) on the status of the CIN and MSI and explored their molecular profiles. A total of 213 colorectal tumors were collected for analysis of DNA ploidy, MSI, loss of heterozygosity (LOH), mutation of p53 (exons 5 to 9), Ki-ras (exons 1 and 2) and BRAF (V599E). Relationships between clinicopathological variables and molecular analyses were analyzed with the chi(2) test (Yates' correction). Kaplan-Meier survival curves were compared using log-rank test. Variables with p < 0.1 were entered into the Cox regression hazard model for multivariate analysis. High microsatellite instability (MSI-H) existed in 19 tumors (8.9%), which were more likely to be right-sided (31.6%) with poor differentiation (26.3%). Seventy-one (33.3%) tumors were diploid and 142 (66.7%) were aneuploid. Mutations in p53, Ki-ras and BRAF were found in 45.1%, 41.8% and 4.2% of tumors, respectively. Based on MSI, and CIN, 3 classes were defined: (i) High microsatellite instability MSI-H tumors: young age, high carcinoembryonic antigen (CEA) level, right colon, poorly differentiated, mucin production, high BRAF mutation, lower allelic loss and relatively good prognosis; (ii) Microsatellite stability (MSS) diploid tumors: right colon, poorly differentiated, less infiltrative tumor, mucin production, lower allelic loss and low p53, BRAF mutation; (iii) MSS aneuploid tumors: more infiltrative invasion, greater allelic loss and high p53 mutation. According to multivariate analysis, tumor stage and p53 mutation were significantly associated with disease progression. The MSS diploid and MSS aneuploid CRCs could be subtyped with p53 mutation and had different prognostic outcome and molecular profiles. The 4-year disease-free survival (DFS) of patients with MSS-diploid, wild-type p53 tumors was 67% and significantly higher than those of patients with MSS-diploid, mutant p53 CRC (30%, p = 0.003). The same trend was found in patients with MSS-aneuploid CRC(wild p53 vs. mutant p53, 64% vs. 41%, p = 0.009). We concluded that CIN, MSI and p53 mutation status might be used as a multiple parameter profile for the prognosis of sporadic colorectal cancer.

Immunohistochemical Mismatch Repair Proteins Expression in Colorectal Cancer

Immunohistochemical (IHC) assessment of the mismatch repair proteins has been proposed as an alternative strategy to molecular biology for evaluating the unstable phenotype of tumors. With the aim of introducing IHC analysis as a routine diagnostic test, the authors compared the expression of MLH1 and MSH2 proteins with a PCR-based microsatellite assay. The concordance rate between the two methods was 90% after IHC evaluation of two different areas of each tumor. These results show that IHC may be as efficient as PCR in detecting unstable phenotype by using only one surgical or biopsy sample.

Contribution of microdissection for the detection of microsatellite instability in colorectal cancer

The determination ofmicrosatellite instability (MSI) is an important step in the identification of familial colorectal cancer such as hereditary nonpolyposis colon cancer. It could also be of interest in the therapeutic management of sporadic cancer. International criteria for the determination of MSI have been published, recommending the use of microdissection. The aim of this work was to evaluate the impact of contaminant normal DNA in tumor samples for MSI assessment in colorectal cancer using a microdissection technique. We performed a comparative analysis of the microsatellite status between total DNA (DNA extracted from whole tumor samples) and microdissected DNA in 3 different regions from 23 cases of colorectal cancer. Six microsatellites were amplified using fluorescent polymerase chain reaction. We analyzed 9 cases with MSI and 14 cases without instability, with similar results between total DNA and microdissected DNA. Moreover, within a same tumor, the MSI phenotype was observed regardless of the region analyzed. Thus, this work shows the reproducibility of the MSI phenotype throughout a tumor. However, we observed a regional heterogeneity of the MSI profile, consisting of variations in the number and the size of unstable alleles within different regions. This result reflects the genetic heterogeneity of colorectal cancer with MSI. In the 14 cases without instability, we observed an increase of more than 60% in the loss of heterozygosity detection rate after microdissection. Thus, this work confirms the contribution of microdissection for loss of heterozygosity assessment.

A novel logistic model based on clinicopathological features predicts microsatellite instability in colorectal carcinomas

High-frequency microsatellite instability has been reported to be associated with good prognosis in colorectal adenocarcinoma. However, methods to assess microsatellite instability (MIN) are based on genetic assays and are not ideally suited to most histopathology laboratories. The aim of the present study was to develop a model for prediction of MIN status in colorectal cancer based on phenotypic characteristics. Clinicopathological features of a cohort of 204 patients with primary colon cancer were retrospectively reviewed following predetermined criteria. Genetic assessment of MIN status was performed on DNA extracted from sections of formalin-fixed, paraffin-embedded specimens by testing a panel of 11 microsatellite markers. Logistic regression analysis generated a mathematical tool capable of identifying colorectal tumors displaying MIN status with a sensitivity of 77.8% and a specificity of 96.8%. Features associated with instability included the proximal location of the lesions, occurrence of solid and/or mucinous differentiation, absence of cribriform structures, presence of peritumoral Crohn-like reaction, expansive growth pattern, high Ki67 proliferative index, and p53-negative phenotype. This approach predicts microsatellite instability in colorectal carcinoma with an overall assigned accuracy of 95.1% and a negative predictive value of 97.8%. Implementation of this tool to routine histopathological studies could improve the management of patients with colorectal cancer, especially those presenting with stage II and III of the disease. It will also assist in identifying a subset of patients likely to benefit from adjuvant chemotherapy.

Microsatellite instability and colorectal cancer prognosis

PURPOSE

Many studies have evaluated the role of high levels of microsatellite instability (MSI) as a prognostic marker and predictor of the response to chemotherapy in colorectal cancer (CRC); however, the results are not conclusive. The aim of this study was to analyze the prognostic significance of high levels of MSI (MSI-H) in CRC patients in relation to fluorouracil-based chemotherapy.

EXPERIMENTAL DESIGN

In three different institutions, 1,263 patients with CRC were tested for the presence of MSI, and CRC-specific survival was then analyzed in relation to MSI status, chemotherapy, and other clinical and pathologic variables.

RESULTS

Two hundred and fifty-six tumors were MSI-H (20.3%): these were more frequently at a less advanced stage, right-sided, poorly differentiated, with mucinous phenotype, and expansive growth pattern than microsatellite stable carcinomas. Univariate and multivariate analyses of 5-year-specific survival revealed stage, tumor location, grade of differentiation, MSI, gender, and age as significant prognostic factors. The prognostic advantage of MSI tumors was particularly evident in stages II and III in which chemotherapy did not significantly affect the survival of MSI-H patients. Finally, we analyzed survival in MSI-H patients in relation to the presence of mismatch repair gene mutations. MSI-H patients with hereditary non-polyposis colorectal cancer showed a better prognosis as compared with sporadic MSI-H; however, in multivariate analysis, this difference disappeared.

CONCLUSIONS

The type of genomic instability could influence the prognosis of CRC, in particular in stages II and III. Fluorouracil-based chemotherapy does not seem to improve survival among MSI-H patients. The survival benefit for patients with hereditary non-polyposis colorectal cancer is mainly determined by younger age and less advanced stage as compared with sporadic MSI-H counterpart.

Determination of TP53 Mutation Is More Relevant Than Microsatellite Instability Status for the Prediction of Disease-Free Survival in Adjuvant-Treated Stage III Colon Cancer Patients

Purpose

Microsatellite instability (MSI), TP53 mutation, and KRAS mutation status have been reported as prognostic factors in colon cancer. Most studies, however, have included heterogeneous groups of patients with respect to cancer stage. We determined the prognostic relevance of high-frequency MSI (MSI-H), TP53 mutations, and KRAS mutations in a well-defined group of patients with stage III colon cancer (N = 391), randomly assigned for adjuvant treatment with fluorouracil-based chemotherapy.

Methods

Three hundred ninety-one tumor specimens were available. MSI was determined in 273 specimens, and mutation analyses of TP53 and KRAS were performed in 220 and 205 specimens, respectively.

Results

In a univariate analysis, MSI-H (44 of 273; 16%) was associated with a longer disease-free survival (DFS; P = .038), but in a multivariate model adjusting for nodal involvement, histology, invasion, and grade of tumor, the association of MSI status with DFS did no longer reach statistical significance, though the risk estimate for microsatellite stability versus MSI-H tumors did not change much. Mutant TP53, found in 116 (53%) of 220 tumors, was associated with a shorter DFS, both in univariate (P = .009) and multivariate analyses (P = .018), whereas KRAS mutations (58 of 205; 28%) did not show any prognostic significance.

Conclusion

Both mutant TP53 and MSI-H seem to be prognostic indicators for disease-free survival, but only TP53 retains statistical significance after adjusting for clinical heterogeneity. Thus, in adjuvantly treated patients with stage III colon cancer, presence or absence of a TP53 mutation should be considered as a better predictor for DFS than MSI status.

Differential Expression of α-Methylacyl Coenzyme A Racemase in Adenocarcinomas of the Small and Large Intestines

Alpha-methylacyl coenzyme A racemase (AMACR), a novel immunomarker for prostatic adenocarcinoma, has recently been shown to be expressed in a number of malignancies including colorectal adenocarcinoma. In the current study, 59 surgically resected primary small intestinal adenocarcinomas (34 ampullary and 25 non-ampullary) were immunohistochemically examined for AMACR expression and compared with 66 colorectal adenocarcinomas (including 24 secondary tumors involving the small intestine by direct extension or metastasis). The results show that no AMACR immunoreactivity was detected in normal-appearing small and large intestinal mucosa. While 41 of 66 (62%) colorectal adenocarcinomas exhibited a variable degree of cytoplasmic staining, only 1 of 25 (4%) non-ampullary and 2 of 34 (6%) ampullary small intestinal adenocarcinomas showed positive AMACR immunoreactivity (P < 0.0001). Interestingly, AMACR appeared to be less frequently expressed in mucinous or poorly differentiated colorectal adenocarcinomas when compared with non-mucinous or better-differentiated counterparts, suggesting an association with microsatellite instability status. These results extend our previous observations that small intestinal adenocarcinomas differ markedly from colorectal adenocarcinomas despite their morphologic similarity. The different AMACR expression patterns may not only provide an additional diagnostic tool in the distinction between adenocarcinomas of the small and large intestinal origins but may also shed light on further understanding of intestinal tumorigenesis.

Microsatellite instability testing in colorectal carcinoma: choice of markers affects sensitivity of detection of mismatch repair-deficient tumors

PURPOSE

Microsatellite instability (MSI) is found in 10% to 15% of sporadic colorectal tumors and is usually caused by defects in DNA mismatch repair (MMR). In 1997, a panel of microsatellite markers including mononucleotide and dinucleotide repeats was recommended by a National Cancer Institute workshop on MSI. We investigated the relationship between instability of these markers and MMR protein expression in a cohort of sporadic colorectal cancer patients.

EXPERIMENTAL DESIGN

Paraffin sections of normal and tumor tissue from 262 colorectal cancer patients were examined for MSI status by PCR amplification and for MMR protein expression using antibodies against hMLH1, hPMS2, hMSH2, and hMSH6.

RESULTS

Twenty-six (10%) of the patients studied had tumors with a high level of MSI (MSI-H). The frequencies of MSI were the same in African-American and Caucasian patients. Each of the MSI-H tumors had mutations in both mononucleotide and dinucleotide repeats and had loss of MMR protein expression, as did two tumors that had low levels of MSI (MSI-L). These two MSI-L tumors exhibited mutations in mononucleotide repeats only, whereas eight of the other nine MSI-L tumors had mutations in just a single dinucleotide repeat. There was not a statistically significant difference in outcomes between patients whose tumors were MMR-positive or MMR-negative, although there was a slight trend toward improved survival among those with MMR-deficient tumors.

CONCLUSIONS

The choice of microsatellite markers is important for MSI testing. Examination of mononucleotide repeats is sufficient for detection of tumors with MMR defects, whereas instability only in dinucleotides is characteristic of MSI-L/MMR-positive tumors.

Impairment of stromelysin-1 transcriptional activity by promoter mutations in high microsatellite instability colorectal tumors

Colorectal tumorigenesis is characterized by the sequential inactivation of a series of tumor suppressor genes (microsatellite-stable tumors) and genetic or epigenetic alterations in mismatch repair genes in nonpoliposic hereditary tumours and 13% to 15% of sporadic colorectal cancer [high microsatellite instability (MSI-H) tumors]. We hypothesized a molecular mechanism for MSI-H colorectal tumors related to matrix metalloproteinase 3 (MMP-3) promoter mutations, down-regulation of MMP-3 expression, and impairment of MMP-9 activation. We have now analyzed the 2.2-kb full MMP-3 promoter to assess the mutation distribution. The mutations found are restricted to the polymorphic region that includes the zinc-binding protein (ZBP-89) binding element. To show that these alterations were the cause of the low expression of this gene, we have generated three constructs with different MMP-3 promoters (wild type and two mutants) and we have expressed them in SW480 human colorectal cells. The basal transcriptional activity of wild-type MMP-3 promoter was much higher than the mutants activity. In addition, 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced transcriptional activity of wild-type MMP-3 promoter was 10-fold higher than the mutants activity. Dexamethasone inhibited the basal transcriptional activity of wild-type MMP-3 promoter and of the two mutants found in the MSI-H subgroup of colorectal tumors. Significantly, dexamethasone almost completely blunted the TPA-induced effect on wild-type MMP-3 promoter transcriptional activity and on the mutants, even below their basal activity. Our data show that mutations found in the polymorphic region of the MMP-3 promoter from MSI-H colorectal tumors impair its basal and induced transcriptional activity, which may contribute to their better clinical outcome.

Microsatellite instability in colorectal cancer is associated with local lymphocyte infiltration and low frequency of distant metastases

Colorectal carcinomas (CRCs) with high microsatellite instability (MSI-H) share clinicopathological features distinctly different from their microsatellite stable (MSS) counterparts. Unlike MSS cancers, MSI-H CRCs occur predominantly in the right-sided colon and are often characterised by a strong lymphocyte infiltration. A poor differentiation pattern is found in most MSI-H CRCs, even though patients with MSI-H carcinomas seem to have a significantly longer survival after surgical resection. To clarify which factors contribute to the obvious paradoxon of a more favourable prognosis of MSI tumours, several clinical and histopathological features as well as the microsatellite status were evaluated in 120 colorectal cancer cases fulfilling clinical criteria (Bethesda) indicative for familial colorectal cancer. Microsatellite instablity status and lymphocyte infiltration were related to tumour stage and patients' follow-up. Statistical analysis confirmed well-known relations, such as enhanced lymphocyte infiltration accompanied by Crohn's like reaction (CLR) in MSI-H cancers (CLR+ in 27 out of 47 MSI-H vs 14 out of 71 MSS CRCs, P<0.001). However, after stratification for depth of local invasion and penetration of the primary tumour, T3 tumours displaying MSI had a significantly lower rate of distant metastases (M1 in four out of 35 MSI-H vs 20 out of 41 MSS CRCs, P<0.001). A similar tendency was observed for CLR-positive CRCs (M1 in six out of 29 CLR+ vs 17 out of 45 CLR− CRCs, P=0.13). In a logistic regression model, the MSI-H phenotype and the presence of CLR were independent predictors of a low UICC stage (P=0.006 and 0.04, respectively). These data, together with the recent definition of highly immunogenic neo-antigens expressed in MSI-H tumour cells, suggest that MSI-H CRCs elicit a protective host response that may prevent metastasis formation.

Predictive factors for response to chemotherapy in colorectal cancer patients

Colorectal cancer represents a major health problem in the western world. A lot of drugs have been employed in treatment of this disease, but only few data are available about predictive factors for response to anticancer treatments in colorectal cancer. Aim of this paper is to review the main data about this investigation field. Using a Medline database search (1966-2003) we reviewed all the relevant papers that investigate clinical and molecular predictors for response to the main drugs used in the treatment of colorectal cancer patients, both in adjuvant and in advanced setting. Moreover we comprehensively reviewed all the data published in abstract form during the most significant international meetings. Our review put in evidence the most important predictive factors for response in colorectal cancer patients treated with anticancer chemotherapy both in adjuvant and in advanced setting. The predictive factors are clustered on the basis of the different anticancer drugs. The results of this review provide the rationale basis for personalizing anticancer treatment in colorectal cancer patients by molecular and clinical features, aiming to improve response rate and reduce toxicities.

Systematic review of microsatellite instability and colorectal cancer prognosis

PURPOSE

A number of studies have investigated the relationship between microsatellite instability (MSI) and colorectal cancer (CRC) prognosis. Although many have reported a better survival with MSI, estimates of the hazard ratio (HR) among studies differ. To derive a more precise estimate of the prognostic significance of MSI, we have reviewed and pooled data from published studies.

METHODS

Studies stratifying survival in CRC patients by MSI status were eligible for analysis. The principal outcome measure was the HR. Data from eligible studies were pooled using standard techniques.

RESULTS

Thirty-two eligible studies reported survival in a total of 7,642 cases, including 1,277 with MSI. There was no evidence of publication bias. The combined HR estimate for overall survival associated with MSI was 0.65 (95% CI, 0.59 to 0.71; heterogeneity P = .16; I(2) = 20%). This benefit was maintained restricting analyses to clinical trial patients (HR = 0.69; 95% CI, 0.56 to 0.85) and patients with locally advanced CRC (HR = 0.67; 95% CI, 0.58 to 0.78). In patients treated with adjuvant fluorouracil (FU) CRCs with MSI had a better prognosis (HR = 0.72; 95% CI, 0.61 to 0.84). However, while data are limited, tumors with MSI derived no benefit from adjuvant FU (HR = 1.24; 95% CI, 0.72 to 2.14).

CONCLUSION

CRCs with MSI have a significantly better prognosis compared to those with intact mismatch repair. Additional studies are needed to further define the benefit of adjuvant chemotherapy in locally advanced tumors with MSI.

Two colons-two cancers: paradigm shift and clinical implications

Embryological and physiological data suggest that proximal (in relation to the splenic flexure) and distal parts of the colon represent distinct anatomical and functional entities. Since 1990, molecular biologists have identified two distinct pathways, microsatellite instability (MSI) and chromosomal instability (CIN), which are involved in the pathogenesis of colon cancer (CC). Thus, a new paradigm has emerged with the discovery that CC is a heterogeneous disease; furthermore recent data have demonstrated that these two distinct pathways in colorectal carcinogenesis are characterized by a different clinical outcome. The implications for the clinicians are twofold; (1) tumors originating from the proximal colon have a better prognosis due to a high percentage of MSI-positive lesions; and (2) location of the neoplasm in reference to the splenic flexure should be documented before group stratification in ongoing trials of adjuvant chemotherapy for CC. In the future, clinical decision-making regarding adjuvant chemotherapy might be stratified according to the MSI status of cancers located proximally to the splenic flexure.

Prognostic implications of hMLH1 and p53 immunohistochemical status in right-sided colon cancer

PURPOSE

Extensive research into the molecular biology of colorectal cancer has identified a plethora of molecular markers reputed to provide independent prognostic information. p53 mutational status has been associated with both improved and reduced survival; however, tumors expressing a particular phenotype associated with defective mismatch repair consistently do better. This study was designed to examine site-specific survival implications of p53 and mismatch repair status.

METHODS

Mismatch repair (hMLH1 and hMSH2) and p53 status was investigated immunohistochemically in 111 proximal colon cancers along with tumor TNM stage, grade, and extramural vascular invasion. Fisher's exact test was used to assess categoric data; univariate and multivariate models compared survival between the respective tumor phenotypes.

RESULTS

Thirty-two percent of tumors showed loss of expression of hMLH1 and in a multivariate analysis were associated with a significant survival advantage after adjustment for tumor stage, p53 status, and extramural vascular invasion (hazard ratio, 0.29; 95 percent confidence interval, 0.1-0.87; P = 0.027). Only two tumors showed loss of expression of hMSH2, which was not related further to survival. Aberrant p53 expression was detected in 39 percent of tumors. Such expression was found to be associated with a significantly reduced survival in univariate analysis (P = 0.037, log-rank test) but not in a multivariate model. Subgroup analysis showed no association between survival and p53 expression in mismatch repair proficient tumors.

CONCLUSIONS

Loss of hMLH1 expression is an independent predicator of improved survival in this series and perhaps the underlying cause of the observed survival difference associated with p53 expression.

Defective mismatch repair in the pathogenesis of low-grade appendiceal mucinous neoplasms and adenocarcinomas

Defective DNA mismatch repair has been proposed as a second pathway for colonic carcinogenesis, particularly in tumors arising in the right colon. We investigated whether tumors arising in the appendix are associated with defective DNA mismatch repair using immunohistochemistry for mismatch repair enzymes hMLH-1, hMSH-2, hMSH-6, and hPMS-2. These immunoassays have been shown to be highly sensitive and specific for defective DNA mismatch repair in sporadic and familial adenocarcinomas. Sporadic adenocarcinomas with defective DNA mismatch repair essentially always show loss of hMLH-1, while loss of hMSH-2, hMSH-6, or hPMS-2 is almost always due to germline mutation. In all, 35 cases of appendiceal epithelial neoplasms were evaluated, comprising 18 low-grade appendiceal mucinous neoplasms confined to the appendix; eight low-grade appendiceal mucinous neoplasms with extra-appendiceal spread (five peritoneum and ovaries, two peritoneum, one ovaries only); and nine invasive adenocarcinomas (three with metastatic disease). All immunohistochemical slides were reviewed by two pathologists. One (11%) invasive adenocarcinoma showed absent expression of hMSH-2 and hMSH-6, but preserved hMLH-1 and hPMS-2 expression. This case was a 26-year-old female with a history of synovial sarcoma who presented with acute appendicitis and appendiceal perforation (median age for other invasive carcinomas, 62 years; range 38-76 years). The appendiceal tumor was a moderately differentiated, colonic-type adenocarcinoma without significant extracellular mucin or tumor-infiltrating lymphocytes. The remaining invasive carcinomas and low-grade appendiceal mucinous neoplasms demonstrated preserved expression of all mismatch repair enzymes, including the seven cases in which extra-appendiceal tumor was also evaluated. We conclude that defective DNA mismatch repair does not play a role in the pathogenesis of low-grade appendiceal mucinous neoplasms. Defective DNA mismatch was found in 11% of invasive carcinomas, likely due to a germline mutation. These findings suggest that sporadic appendiceal neoplasia rarely arises through the defective DNA mismatch repair (mutator) pathway.

Genetic Alterations in Locally Advanced Stage II/III Colon Cancer: A Search for Prognostic Markers

Heterogeneity in advanced colon cancer leads to different results from adjuvant chemotherapy. To identify groups of patients who may need adjuvant treatment, molecular staging and correlation with clinical data may be helpful in classifying histologically similar tumors. Colon cancer develops through a multistep process with an accumulation of multiple genetic alterations that are often the cause of a form of genomic instability. The 2 best known mechanisms of genomic instability are chromosomal instability (CIN) and microsatellite instability (MSI). The CIN phenotype is found in approximately 85% of sporadic colon cancers and is characterized by aneuploidy, multiple chromosomal rearrangements, and an accumulation of somatic mutations in oncogenes such as K-ras and tumor suppressor genes such as TP53 and APC. The MSI phenotype is associated with small insertions and deletions mainly in repetitive sequences (microsatellites) and is found in approximately 15% of cases. This instability, often referred to as high-frequency MSI (MSI-H), is caused by defects of the mismatch repair system, which is involved in repairing DNA errors that arise during DNA replication. Clear-cut correlations between the somatic genetic alterations in tumors and the clinical behavior of the tumor are rare. Only a few markers, such as MSI-H and TP53, seem to have a prognostic value. Mutations in the TP53 gene are associated with an aggressive tumor growth and subsequent reduced survival, whereas MSI-H seems to be correlated with a favorable outcome. In general, predicting biologic behavior of in particular stage III colon cancers is difficult and remains a great clinical problem.

Association between recurrence of sporadic colorectal cancer, high level of microsatellite instability, and loss of heterozygosity at chromosome 18q

PURPOSE

Microsatellite instability and loss of heterozygosity of chromosomes 18q, 8p, and 4p are genetic alterations commonly found in colorectal cancer. We investigated whether these genetic markers allow for the stratification of patients with Stage II to III colorectal cancer into groups with different recurrence risks, and with different prognoses.

METHODS

Tumors of 113 patients were evaluated for loss of heterozygosity of chromosomes 18q, 8p, and 4p and for microsatellite instability by use of six microsatellite markers. Genetic alterations involving each of these genetic markers were examined for association with disease recurrences and survival.

RESULTS

Loss of heterozygosity of chromosomes 18q, informative in 96 percent of cases, in Stage III tumors was associated with higher risk of overall recurrence ( P< 0.001), local recurrence ( P< 0.001), distant metastases ( P< 0.001), decreased overall survival ( P= 0.002), and disease-free survival ( P< 0.001). The recurrence rates and survival rates among patients with Stage II colorectal cancer were independent of loss of heterozygosity of chromosome 18q. Stage III and loss of heterozygosity of chromosome 8p also were associated with a higher risk of recurrences when these factors were considered individually. In multivariate analysis, only loss of heterozygosity of chromosome 18q was independently associated with risk of recurrences ( P < 0.001) and with disease-free survival ( P= 0.001). No correlation was observed between microsatellite instability and recurrence rates. However, microsatellite instability was associated with improved overall survival ( P= 0.04) and with a longer disease-free interval ( P= 0.002). Only in five cases (16.7 percent) was it possible to perform resection of recurrences; two of these patients had microsatellite instability tumor. In no cases was it possible to resect recurrence of tumors with loss of heterozygosity of chromosome 18q.

CONCLUSIONS

Loss of heterozygosity of chromosome 18q is an informative genetic marker, which in resected Stage III colorectal cancer can be used to predict recurrences and survival. Microsatellite instability identified cases that, even in the case of recurrence, have a more favorable prognosis.

Reduced expression of cytokeratin 20 in colorectal carcinomas with high levels of microsatellite instability

High levels of microsatellite instability (MSI-H) result from abnormal nucleotide mismatch repair in a subset of sporadic colorectal carcinomas (CRC) and in most CRC of hereditary non-polyposis colorectal cancer syndrome. CRC with MSI-H have distinctive clinical-pathologic features, but the immunophenotype has not been studied extensively. We evaluated immunohistochemical expression of cytokeratin 7 (CK7), cytokeratin 20 (CK20), and pancytokeratin (panCK) in 44 CRC from 22 paired MSI-H and microsatellite-stable (MSS) cases matched for clinical-pathologic characteristics. The mean percentage of CK20+ tumor cells was 84 +/- 6% in MSS CRC but only 37 +/- 8% in MSI-H CRC (P = 0.0007). Thirty-two percent (7/22, 95% confidence interval 14-55%) of MSI-H CRC were CK20-, as contrasted with 9% (2/22, 95% CI 1-29%, P = 0.13) of MSS CRC. CK20 expression was inversely correlated with levels of MSI (rs = -0.45, P = 0.006). CK7+ was infrequent (16%, 7/44, 95% CI 7-30%) and panCK+ was universal, with no significant differences between MSI-H and MSS CRC. Our study shows that decreased or even absent CK20 expression is a phenotypic characteristic of MSI-H CRC and that MSI-H explains much of the subset of CRC that lack CK20 expression. Our results also indicate that regulation of CK20 gene expression involves molecular pathways that are altered by MSI-H.

Clinicopathological significance of microsatellite instability and mutated RIZ in colorectal cancer

BACKGROUND

Several studies have shown that microsatellite instability (MSI) is related to favourable survival in colorectal cancer patients but there are controversial results. Tumour suppressor gene RIZ is a susceptible mutational target of MSI. However, its clinicopathological significance has not been investigated. We investigated the prognostic significance of MSI in Swedish colorectal cancer patients and the clinicopathological significance of RIZ mutations.

PATIENTS AND METHODS

We analysed 438 colorectal adenocarcinomas for MSI by microsatellite analysis. Among them, 29 MSI and 28 microsatellite stable (MSS) tumours were examined for RIZ mutations by DNA sequencing.

RESULTS

MSI (13% of 438 cases) was not associated with survival (rate ratio = 0.97, 95% confidence interval = 0.57-1.64, P = 0.90), although it was related to proximal tumour (P <0.001), poor differentiation and mucinous carcinomas (P <0.001), multiple tumours (P = 0.01) and negative/weak expression of hMLH1 (P = 0.03). RIZ mutations were detected in 31% of 29 MSI tumours but in none of the 28 MSS tumours. The mutations were related to female (P = 0.01), proximal tumour (P = 0.01), stage B (P = 0.01) and poor differentiation (P = 0.047).

CONCLUSIONS

MSI was not a prognostic factor in the Swedish patients included in this study. Clinicopathological variables associated with RIZ mutations might be a consequence of the MSI characteristics.

Primary epithelial neoplasms and other epithelial lesions of the appendix (excluding carcinoid tumors)

Epithelial tumors of the appendix range from low-grade mucosal-based tumors which, when confined to the appendix, have an excellent prognosis but, once outside the appendix, have a fair prognosis and often a prolonged disease course, to high grade invasive carcinomas that are rapidly fatal. Low grade mucinous neoplasms may rupture and spread to the peritoneum as pseudomyxoma peritonei, and the nomenclature of these tumors has been the subject of considerable disagreement among pathologists; the designation "low grade appendiceal mucinous neoplasm" has recently been proposed for reasons discussed herein. Demonstrating rupture of these neoplasms may require particularly diligent gross and microscopic evaluation as the rupture site often heals over leaving only subtle evidence of its presence. Invasive adenocarcinomas are often mucinous and may also spread to the peritoneum. Against this backdrop, the clinical and pathologic features of low grade appendiceal mucinous neoplasms and mucinous adenocarcinomas, as well as other types such as typical colorectal type and signet-ring cell type, are reviewed. In addition, emerging entities, serrated polyps and serrated adenomas, whose significance is only beginning to be understood, are considered. Retention cysts, hyperplastic polyps, and diffuse mucosal hyperplasia, although not necessarily neoplastic, are reviewed here as they may enter into the differential diagnosis of appendiceal mucinous neoplasms.

Hypermethylation of the hMLH1 promoter with absent hMLH1 expression in medullary-type poorly differentiated colorectal adenocarcinoma in the elderly

To clarify the significance of hMLH1 promoter hypermethylation in the development of medullary-type poorly differentiated colorectal adenocarcinoma, we studied the status of promoter methylation and hMLH1 expression in 23 medullary-type and 12 pleomorphic-type carcinomas, as well as the pathology and microsatellite status. In medullary-type carcinomas, the percentages of cases with promoter methylation (83%) and an absence of hMLH1 expression (91%) were significantly higher than in pleomorphic-type carcinomas (14 and 17%), respectively. The rate of microsatellite instability in the medullary type was significantly higher than that of the pleomorphic type (87 vs 40%, P<0.01). Compared with pleomorphic-type carcinomas, medullary-type carcinomas were significantly associated with hMLH1 promoter methylation, absent expression of hMLH1 protein, microsatellite instability, as well as a proximal location, a Crohn's-like lymphoid reaction, a low incidence of lymph node metastasis, and a favorable outcome. Medullary-type carcinomas accumulated with advancing age, especially in the female. These results indicated that hMLH1 hypermethylation, concurrent with a lack of its protein expression, may play an important role in the development of medullary-type poorly differentiated colorectal adenocarcinomas in the elderly.

Inactivation of p16INK4a by CpG hypermethylation is not a frequent event in colorectal cancer

BACKGROUND AND OBJECTIVES

Gene promoter hypermethylation is common in colorectal cancer and is associated with transcriptional silencing. However, the clinicopathological significance of p16(INK4a) gene silencing with hypermethylation is unknown. Therefore, the aim of this study was to analyze loss of p16 expression and its relationship to hypermethylation in sporadic colorectal cancer.

METHODS

Tissue from 426 colorectal cancers underwent histological analysis. Immunohistochemistry was performed for p16 expression. Fresh tumor DNA was analyzed for microsatellite instability (MSI) and the presence of K-ras mutations. In addition, DNA was bisulphite-modified and analyzed for p16(INK4a) promoter methylation by methylation-specific PCR.

RESULTS

There were 25% of tumors with p16(INK4a) promoter hypermethylation. These tumors were associated with older patients, right-sidedness, MSI and were poorly differentiated, mucinous, and had intraepithelial and peritumoral lymphocytes and a Crohn's-type lymphocytic reaction (P < 0.05). However, only right-sidedness was significant on multivariate analysis (P < 0.001). Only 8.1% of tumors did not express p16, and this was associated with hypermethylation (P < 0.05).

CONCLUSION

p16(INK4a) promoter methylation, although common in colorectal cancer, does not result in a clinicopathologically distinct subgroup of tumors and infrequently results in transcriptional silencing. This suggests that p16(INK4a) gene inactivation does not have an important role in the pathogenesis of sporadic colorectal cancer.

Histopathology and mismatch repair status of 458 consecutive colorectal carcinomas

Defects in the mismatch repair (MMR) genes hMLH1 and hMSH2 have been found in 10% to 20% of sporadic colorectal carcinomas and also many cases of hereditary nonpolyposis colorectal cancer syndrome. Patients with these tumors have an improved prognosis and may show greater sensitivity to chemotherapy. We examined 458 resected colorectal carcinomas from 430 consecutive patients and used immunohistochemistry to determine which tumors lacked expression of these genes (MMR-d). We correlated the status of MMR-d or "intact" expression with stage, site, and histology. Eighty-nine of 458 tumors (19.4%) were MMR-d, including 80 hMLH1 and 9 hMSH2 tumors. A total of 6% of patients had synchronous tumors, and 37.7% of these were MMR-d (P=0.0008). A high proportion of patients with previous breast cancer (4 of 6 patients) had hMLH1-defective colorectal carcinomas. MMR-d tumors presented at an earlier stage than intact tumors, and the node-positive MMR-d tumors were less likely than intact tumors to have pericolonic extranodal tumor deposits (18.2% vs. 44%). The proportion of tumors at each site that were MMR-d increased progressively from cecum (32%) to ascending (35%) to transverse colon, where 41% of all tumors were defective. The proportions then rapidly decreased, reaching the lowest rate (4.7%) in the rectum. Both types of MMR-d tumors more often had expansive borders, intraepithelial lymphocytosis, peritumoral lymphoid, and Crohn's-like lymphoid responses than the intact tumors; the frequencies of these features diminished with advancing stage. Tumor budding was less common in stage II and III MMR-d tumors than in intact tumors. Keloid and myxoid type stromas correlated with stage and vascular invasion and were not related to mismatch repair status. Significant differences existed between the hMLH1 and hMSH2 tumors. The reported right-sided preponderance of MMR-d tumors is due to most hMLH1, but not hMSH2, tumors being found there (87.5% vs. 44.4%). hMSH2 tumors were most common in the rectum (55.6%). Mucinous tumors were common in hMLH1 tumors (36.3%) but not in hMSH2 tumors (11.1%). hMLH1 tumors were most likely to be poorly differentiated (70%), which was uncommon with hMSH2 tumors (22.2%). hMSH2 tumors were more likely to be confined to the wall (66.7%) than hMLH1 (20%) or intact tumors (23%). We conclude that hMLH1 and hMSH2-defective tumors have distinctly differing histologic features from each other.

Colorectal cancer relapse: allelic alterations associated with tumour marker overexpression

The objective of the present study was to assess the prognostic value of allelic alterations in comparison with clinical prognostic factors (age and gender, clinical stage, lymph node involvement, tissue tumour marker expression) and clinical outcomes (disease relapse and overall survival time) in colorectal cancer patients. Polymerase chain reaction was performed on the DNA of 72 colorectal samples (from 36 colorectal cancer patients) using primers D17S513 and D17S514. Carbohydrate antigen 19-9 (CA 19-9) marker was determined in tumour sections by enzyme immunoassay. Tumours were considered to exhibit allelic alterations if the microsatellite region adjacent to the p53 locus in chromosome 17 either gained or lost repeated sequences. Allelic alterations were detected in 44% of tumour samples. Patients with more than 3 involved lymph nodes had more frequent allelic alterations (p < 0.002). The allelic alteration status was compared with tumour CA 19-9 expression, which showed statistically significantly higher values within the allelic alterations group (p < 0.005). Multivariate analyses confirmed that tumours with allelic alterations had a higher probability of disease relapse (odds ratio 7.3, p = 0.01). This is the first report showing an association between allelic alteration and overexpression of a tissue tumour marker protein and established risk factors. These results could be considered useful additional prognostic information for colorectal cancer.

Prognostic molecular markers for planning adjuvant chemotherapy trials in Dukes' B colorectal cancer patients: how much evidence is enough?

The benefit of postoperative adjuvant chemotherapy in patients with Dukes' B colorectal cancer is still uncertain and its routine use is not recommended. Prognostic biomarkers may be useful for identifying high-risk patients with resected, node-negative disease, and this stratification may represent an innovative strategy for designing adjuvant chemotherapy trials. Featured prognostic molecular markers can be divided into the following categories: cell proliferation indices (Ki-67, Mib-1, proliferating cell nuclear antigen); oncogenes/tumor suppressor genes [p53, K-ras, Deleted in Colorectal Cancer (DCC), Bcl-2, c-erbB2]; DNA repair (microsatellite instability); markers of angiogenesis (vascular count, vascular endothelial growth factor); markers of invasion/metastasis (plasminogen-related molecules, matrix metalloproteinases); and biochemical markers (thymidylate synthase). Studies that have investigated their prognostic role in Dukes' B colorectal cancer patients are reviewed here. Current data do not provide sufficient evidence for the incorporation of available prognostic biomarkers into clinical practice. However, a biomarker-based approach could be an effective strategy for improving results of postoperative adjuvant treatments in high-risk Dukes' B colorectal cancer patients. Markers of altered DCC function have shown promising prognostic role and sufficient prevalence in retrospective investigations and they deserve further assessment in prospective studies.

Sporadic colorectal cancers with defective mismatch repair display a number of specific morphological characteristics: relationship between the expression of hMLH1 and hMSH2 proteins and clinicopathological features of 273 adenocarcinomas

AIMS

The aim of this study was to assess the independent value of pathological criteria in the diagnosis of mismatch repair (MMR)-defective sporadic colorectal cancers.

METHODS AND RESULTS

Resected colorectal adenocarcinomas (n = 273) were reviewed in order to identify a number of specific morphological features of MMR-defective carcinomas. Of the 273 cases, 35.2% were right-sided and 5.9% were poorly differentiated. Focal extracellular mucin secretion was seen in 5.1% of cases and a stromal follicular reaction in 4.6%. The expression of the two major MMR proteins hMLH1 and hMSH2 was studied by immunohistochemistry. Carcinomas were considered deficient in the MMR system when a loss of nuclear signal in neoplastic cells was observed for one of the proteins. Such an extinction was seen in 37 of the cases (13.6%). The hMLH1 protein was the one most frequently altered (86.5%). After multivariate analysis, three independent factors were significantly associated with MMR deficiency: proximal location [odds ratio (OR) = 9.30; 95% confidence interval (CI) 2.79, 30.98], the presence of a true stromal follicular reaction (OR = 13.60; 95% CI 2.98, 62.00) and poor differentiation (OR = 8.33; 95% CI 1.63, 40.32).

CONCLUSIONS

These results confirm that sporadic colorectal MMR-defective adenocarcinomas display certain specific morphological characteristics. However, these pathological features are not sufficiently predictive and immunohistochemistry is needed to identify such tumours accurately.

[Clinical, pathological and molecular prognostic factors in colorectal carcinomas]

Various aspects of the progression and prognosis of colorectal carcinoma have been investigated in numerous publications during recent years. An exact macroscopic and microscopic examination is still of basic importance but different factors of the molecular pathogenesis of colorectal carcinoma could be described by immunohistochemistry and molecular biology. Furthermore, they have been evaluated regarding their importance for the course of disease and prognosis and in particular, the different pathways of carcinogenesis and microsatellite instability were included. The detection of micrometastasis was investigated applying mostly molecular genetic methods. Numerous oncogenes, tumor suppressor genes and regulators of the cell cycle, markers of proliferation and apoptosis, cell adhesion antigens and angiogenetic factors were characterized with regard to their prognostic potential. In the future, so-called response predictors will presumably gain a certain relevance in the context of neoadjuvant (radiotherapy) chemotherapy. The present review summarizes these results and discusses the future clinical relevance.

High-frequency microsatellite instability predicts better chemosensitivity to high-dose 5-fluorouracil plus leucovorin chemotherapy for stage IV sporadic colorectal cancer after palliative bowel resection

The influence of MSI on treatment outcome of colorectal cancers remains unclear and deserves further investigation. We recruited 244 patients with stage IV sporadic colorectal cancers for our study, based on appropriate eligibility criteria. Patients were nonrandomly allocated to 2 treatment groups of either with or without high-dose 5-FU plus leucovorin chemotherapy (HDFL, 5-FU 2,600 mg/m(2) leucovorin 300 mg/m(2) maximum 500 mg). Each treatment group was further divided into 2 subgroups according to high-frequency MSI (MSI-H) status. MSI-H was defined as the appearance of MSI in at least 2 of the 5 examined chromosomal loci (BAT-25, BAT-26, D5S346, D2S123, D17S250). We compared clinicopathologic parameters, p53 overexpression and overall survival between the groups. In addition, 4 subgroups were identified as follows: MSI-H(+)HDFL(+), n = 35; MSI-H(-)HDFL(+), n = 134; MSI-H(+)HDFL(-), n = 17; MSI-H(-)HDFL(-), n = 58. There was no significant difference of background clinicopathologic data between the HDFL(+) and HDFL(-) treatment groups (p > 0.05). Survival analyses indicated that the patients of subgroup MSI-H(+)HDFL(+) survived significantly longer than those of subgroup MSI-H(-)HDFL(+), with median survival times of 24 (95% CI 20.2-27.9) and 13 (95% CI 11.6-14.4) months, respectively (p = 0.0001, log-rank test). In contrast, in patients without chemotherapy, the prognosis was poor irrespective of MSI status, with median survival times of 7.0 (95% CI 4.6-9.4) and 7.0 (95% CI 6.1-7.9) months in the MSI-H(+)HDFL(-) and MSI-H(-)HDFL(-) subgroups, respectively (p = 0.8205, log-rank test). MSI-H cancers responded significantly better to HDFL (p = 0.001), with a mean response rate of 65.71% (95% CI 49.98-81.44%) in subgroup MSI-H(+)HDFL(+) compared to 35.07% (95% CI 26.99-43.15%) in subgroup MSI-H(-)HDFL(+). There appeared to be no preferential metastatic site where response to HDFL can be predicted based on the MSI status of the primary tumor. Toxicity to HDFL was similarly minimal between MSI-H(+) and MSI-H(-) patients (p > 0.05). Multivariate analysis of all patients further indicated that MSI-H and chemotherapy were independent favorable prognostic parameters (p < 0.05). Thus, the better prognosis of stage IV sporadic colorectal cancers with MSI-H may be associated with better chemosensitivity, rather than lower aggressiveness in biologic behavior.

Microsatellite instability and intratumoural heterogeneity in 100 right-sided sporadic colon carcinomas

Microsatellite instability has been proposed as an alternative pathway of colorectal carcinogenesis. The aim of this study was to evaluate the interest of immunohistochemistry as a new tool for highlighting mismatch repair deficiency and to compare the results with a PCR-based microsatellite assay. A total of 100 sporadic proximal colon adenocarcinomas were analysed. The expression of hMLH1, hMSH2 and hMSH6 proteins evaluated by immunohistochemistry was altered in 39% of the cancers, whereas microsatellite instability assessed by PCR was detected in 43%. There was discordance between the two methods in eight cases. After further analyses performed on other tumoural areas for these eight cases, total concordance between the two techniques was observed (Kappa=100%). Our results demonstrate that immunohistochemistry may be as efficient as microsatellite amplification in the detection of unstable phenotype provided that at least two samples of each carcinoma are screened, because of intratumoural heterogeneity.

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.

Does MSI-low exist?

Microsatellite instability is a well-recognised phenomenon. Ten to 15% of sporadic colorectal cancers with a high level of MSI form a well defined group with distinct clinicopathological features. The set of tumours with low level of microsatellite instability (MSI-low), though widely referred to, is not a clearly defined group. The definitions of MSI-low have varied among groups and between different studies from the same group. Some studies have found associations between the MSI-L phenotype and molecular features, notably a higher frequency of K-ras mutations, and, possibly, methylation of methylguanine methyltransferase. Two recent independent studies, however, showed respectively that 68% and 79%, non-MSI-H cancers showed some MSI and could therefore be classed nominally as MSI-L. There was no evidence for a qualitatively discrete MSI-L group, but quantitative differences in the level of MSI were found.

Prediction of the response of colorectal cancer to systemic therapy

Adjuvant chemotherapy with fluorouracil and folinic acid improves overall survival for resected carcinoma of the colon of Dukes' stage C by 10-12%. In metastatic disease, response rates with fluorouracil-based regimens are about 25%. Combination with newer agents such as irinotecan and oxaliplatin can improve response rates to more than 50% in selected patients. New treatments with novel molecular targets will soon be entering clinical use. Despite these improvements, many patients undergo chemotherapy for resistant cancer, thus incurring side-effects without benefit. Expression of particular genes can be tested at the protein or RNA level and can be correlated with response or resistance to particular systemic therapies. Thus, predictive-factor testing of tumour biopsy samples may allow us to select chemotherapy or immunotherapy treatments with a high likelihood of benefit for the individual patient.

Comparison of microsatellite instability and chromosomal instability in predicting survival of patients with T3N0 colorectal cancer

BACKGROUND

At least 2 apparently independent mechanisms, microsatellite instability (MSI) and chromosomal instability, are implicated in colorectal tumorigenesis. Their respective roles in predicting clinical outcomes of patients with T3N0 colorectal cancer remain unknown.

METHODS

Eighty-eight patients with a sporadic T3N0 colon or rectal adenocarcinoma were followed up for a median of 67 months. For chromosomal instability analysis, Ki-ras mutations were determined by single-strand polymerase chain reaction, and p53 protein staining was studied by immunohistochemistry. For MSI analysis, DNA was amplified by polymerase chain reaction at 7 microsatellite targets (BAT25, BAT26, D17S250, D2S123, D5S346, transforming growth factor receptor II, and BAX).

RESULTS

Overall 5-year survival rate was 72%. p53 protein nuclear staining was detected in 39 patients (44%), and MSI was detected in 21 patients (24%). MSI correlated with proximal location (P <.001) and mucinous content (P <.001). In a multivariate analysis, p53 protein expression carried a significant risk of death (relative risk = 4.0, 95% CI = 1.6 to 10.1, P =.004). By comparison, MSI was not a statistically significant prognostic factor for survival in this group (relative risk = 2.2, 95% CI = 0.6 to 7.3, P =.21).

CONCLUSIONS

p53 protein overexpression provides better prognostic discrimination than MSI in predicting survival of patients with T3N0 colorectal cancer. Although MSI is associated with specific clinicopathologic parameters, it did not predict overall survival in this group. Assessment of p53 protein expression by immunocytochemistry provides a simple means to identify a subset of T3N0 patients with a 4-times increased risk for death.

Emerging pathways in colorectal-cancer development

The past decade has seen the emergence of new pathways in the development of colorectal cancer. There is now clear evidence that subsets of these tumours do not show chromosomal instability and do not follow the suppressor pathway. Instead, about 15% of colorectal cancers are characterised by microsatellite instability (MSI). This feature arises through defective DNA mismatch repair, which is related either to a germline mutation (as in hereditary non-polyposis colorectal carcinoma) or to failure to express a mismatch-repair gene. CpG-island methylation has been linked to sporadic cancers with a high frequency of MSI. This type of methylation leads to loss of gene expression when it occurs in the promoter region of a gene. Tumours may have high or low type C (cancer-related) CpG-island methylation. When methylation affects hMLH1 (mismatch repair gene), the resultant cancer has high MSI.

Microsatellite instability

Unlike aneuploidy, considered to be the cardinal feature of malignant tumors ever since the chromosomal analysis of neoplastic cells became technically feasible, a second pathway toward malignancy has emerged over the past decade that is not characterized by gross aneuploidy but, instead, by inactivation of the DNA mismatch repair system, leading to a hypermutable state in which simple repetitive DNA sequences are unstable during DNA replication. Although mutations of many of these microsatellite sequences are presumably innocuous, because they do not occur in the coding or regulatory regions of genes, other such sequences are critically located in the coding regions of genes involved in the regulation of cell growth. First discovered in the rather uncommon hereditary nonpolyposis colorectal cancer syndrome, where there is an inactivating germline mutation in one of the DNA mismatch repair genes and most of the tumors show microsatellite instability, the latter phenomenon has since been implicated in about 15% of sporadic colorectal cancers, as well as in cancers at several other sites, such as the endometrium. Tumors showing microsatellite instability are generally near-diploid, are at a low stage of development, have a favorable prognosis, and, in the colon, are commonly located on the right side. In recent years, epigenetic phenomena, including hypermethylation and loss of imprinting, have come to be recognized as having a significant bearing on the development of these tumors.