Microsatellite instability is a favorable prognostic indicator in patients with colorectal cancer receiving chemotherapy

Growth differentiation factor 15: a prognostic marker for recurrence in colorectal cancer

BACKGROUND

Growth differentiation factor 15 (GDF15) belongs to the transforming growth factor beta superfamily and has been associated with activation of the p53 pathway in human cancer. The aim of this study was to assess the prognostic value of GDF15 in patients with colorectal cancer (CRC).

METHODS

Immunohistochemistry and tissue microarrays were used to analyse GDF15 protein expression in 320 patients with CRC. In a subgroup of 60 patients, the level of GDF15 protein in plasma was also measured using a solid-phase proximity ligation assay.

RESULTS

Patients with CRC with moderate to high intensity of GDF15 immunostaining had a higher recurrence rate compared with patients with no or low intensity in all stages (stages I-III) (HR, 3.9; 95% CI, 1.16-13.15) and in stage III (HR, 10.32; 95% CI, 1.15-92.51). Patients with high plasma levels of GDF15 had statistically shorter time to recurrence (P=0.041) and reduced overall survival (P=0.002).

CONCLUSION

Growth differentiation factor 15 serves as a negative prognostic marker in CRC. High expression of GDF15 in tumour tissue and high plasma levels correlate with an increased risk of recurrence and reduced overall survival.

Microsatellite instability in colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is the third most common cancer in the world. In 75% CRC develops sporadically, in 25% hereditary or as a consequence of inflammatory bowel disease. CRC carcinogenesis develops over many years. The cause of CRC in 85% is chromosomal instability (CIN) and in 15% microsatellite instability (MSI-H), where hereditary nonpolyposis colorectal cancer (HNPCC) represents 10-20%. Microsatellite sequences (MS) are repeated sequences of short stretches of DNA all over the genome. Microsatellite stability (MSS) means MS are the same in each cell of an individual, whereas microsatellite instability (MSI-H) means MS differ in normal and cancer cells of an individual. The cause of MSI-H is a damaged mismatch repair mechanism (MMR), with the most important MMR proteins being MSH2, MLH1 and MSH6.

CONCLUSIONS

MSI-H seems to be an important prognostic factor in CRC and an important predictive factor of CRC chemotherapeutic treatment efficacy. Clinical trials conducted until now have shown contradictory findings in different chemotherapeutic settings, adjuvant and palliative; therefore MSI-H is going to be the object of the future research. The future of cancer treatment is in the individualized therapy based on molecular characteristics of the tumour, such as MSI-H in CRC.

Personalized medicine and oncology practice guidelines: a case study of contemporary biomarkers in colorectal cancer

Predictive and prognostic biomarkers offer a potential means to personalize cancer medicine, although many reach the market-place before they have been validated, and their adoption is often hindered by variable clinical evidence. Because of this variability in supporting evidence, clinical practice guidelines formulated by panels of subspecialty experts may be particularly important in guiding stakeholders' acceptance and use of new personalized medicine biomarker tests and other nascent technologies. This article provides a structured review of the clinical evidence supporting 4 contemporary biomarker tests in colorectal cancer: K-ras and B-raf mutation analyses, mismatch repair protein testing, and the Oncotype DX Colon Cancer Assay. All 4 tests have been evaluated for guideline inclusion by the NCCN Guidelines Panel for Colon Cancer. This case study shows significant variability in the level of clinical evidence associated with these tests. In the cases of B-raf and mismatch repair protein testing, the available evidence is also inconsistent as it pertains to the specific NCCN Guideline recommendation. Based on this uncertainty in the evidence base, the authors conclude that expert clinical judgment, experience, and consensus may be more heavily weighted than published clinical trial data in the evaluation of new personalized medicine biomarker tests. Potential implications of this conclusion and future directions for research are discussed.

Cyclin E and histone H3 levels are regulated by 5-fluorouracil in a DNA mismatch repair-dependent manner

Several studies indicate that the DNA mismatch repair (MMR) system may trigger cytotoxicity upon 5-fluorouracil (5-FU) recognition, but signaling pathways regulated by MMR in response to 5-FU are unknown. We hypothesize that recognition of 5-FU in DNA by MMR proteins trigger specific signaling cascades that results in slowing of the cell cycle and cell death. Whole human genome cDNA microarrays were used to examine relative signaling responses induced in MMR-proficient cells after 5-FU (5 μM) treatment for 24 hours. Analysis revealed 43 pathways differentially affected by 5-FU compared to control (P 1.4-fold) and downregulated cdc25C, cyclins B1 and B2, histone H2A, H2B, and H3 (< -1.4-fold) over control. Cell cycle analysis revealed a G1/S arrest by 5-FU that was congruent with increased cyclin E and decreased cdc25C protein expression. Importantly, with knockdown of hMLH1 and hMSH2, we observed that decreased histone H3 expression by 5-FU was dependent on hMLH1. Additionally, 5-FU treatment dramatically decreased levels of several histone H3 modifications. Our data suggest that 5-FU induces a G1/S arrest by regulating cyclin E and cdc25C expression, and MMR recognition of 5-FU in DNA may modulate cyclin E to affect the cell cycle. Furthermore, MMR recognition of 5-FU reduces histone H3 levels that could be related to DNA access by proteins and/or cell death during the G1/S phase of the cell cycle.

Clinical, laboratory and molecular factors predicting chemotherapy efficacy and toxicity in colorectal cancer

Colorectal cancer (CRC) treatment has evolved significantly over the last ten years with the use of active chemotherapeutic agents including fluoropyrimidines, oxaliplatin and irinotecan plus targeted monoclonal antibodies bevacizumab, cetuximab and panitumumab. The addition of newer chemotherapeutic agents and targeted therapies has improved patient outcomes at the cost of increased toxicity with not all patients benefiting from these treatments. It is necessary for clinicians to more accurately predict clinical outcomes particularly in the predominantly elderly CRC patient population. This review aims to summarise existing data regarding the use of clinical and laboratory variables plus molecular markers in predicting response, survival and toxicity to chemotherapy agents and targeted monoclonal antibodies currently used in the treatment of CRC.

Mismatch repair protein expression is an independent prognostic factor in sporadic colorectal cancer

Abstract Background. Mismatch repair (MMR) status has been reported as a prognostic and predictive factor in sporadic colorectal cancer (CRC). The purpose of this study was to determine the prognostic and predictive value of MMR protein expression in the adjuvant setting. Patients and methods. The MMR status in the primary tumor was retrospectively assessed on paraffin-embedded formalin-fixed samples from 1 006 patients with sporadic CRC (488 stage II and 518 stage III) using immunohistochemical analysis (IHC) of MLH1 and MSH2 expression. The patients were included in adjuvant Nordic trials between 1991 and 1996 randomly assigned to surgery alone or surgery plus adjuvant 5-fluorouracil (5-FU)-based chemotherapy. Data was censored at 120 months after surgery. Results. One hundred fifty-seven patients (15.6%) showed a loss of MMR protein expression (139 MLH1 negative, 15 MSH2 negative and 3 MLH1 and MSH2 negative) and were classified as MMR protein negative. A normal MMR protein expression was found in 849 patients who were defined as MMR protein positive. MMR protein expression was a significant prognostic marker in the entire study group with a better overall survival (OS) among patients with MMR protein negative tumors compared to patients with MMR protein positive tumors (p=0.01). In a multivariate analysis the MMR protein expression was significantly associated with OS, (HR 0.70 [95% CI, 0.40 to 0.99]; p=0.01). The MMR status did not predict survival benefit from adjuvant 5-FU-based chemotherapy. Conclusion. This study reveals that IHC of MLH1 and MSH2 expression can yield important prognostic information but is not a predictive factor for adjuvant 5-FU-based chemotherapy in sporadic CRC.

DNA mismatch repair deficiency in sporadic colorectal cancer and Lynch syndrome

DNA mismatch repair (MMR) deficiency is one of the best understood forms of genetic instability in colorectal cancer (CRC), and is characterized by the loss of function of the MMR pathway. Failure to repair replication-associated errors due to a defective MMR system allows persistence of mismatch mutations all over the genome, but especially in regions of repetitive DNA known as microsatellites, giving rise to the phenomenon of microsatellite instability (MSI). A high frequency of instability at microsatellites (MSI-H) is the hallmark of the most common form of hereditary susceptibility to CRC, known as Lynch syndrome (LS) (previously known as hereditary non-polyposis colorectal cancer syndrome), but is also observed in approximately 15-20% of sporadic colonic cancers (and rarely in rectal cancers). Tumour analysis by both MMR protein immunohistochemistry and DNA testing for MSI is necessary to provide a comprehensive picture of molecular abnormality, for use in conjunction with family history data and other clinicopathological features, in order to distinguish LS from sporadic MMR-deficient CRC. Identification of the gene targets that become mutated in MMR-deficient tumours may explain, at least in part, some of the clinical, pathological and biological features of MSI-H CRCs and holds promise for developing novel therapeutics.

Defective mismatch repair as a predictive marker for lack of efficacy of fluorouracil-based adjuvant therapy in colon cancer

PURPOSE

Prior reports have indicated that patients with colon cancer who demonstrate high-level microsatellite instability (MSI-H) or defective DNA mismatch repair (dMMR) have improved survival and receive no benefit from fluorouracil (FU) -based adjuvant therapy compared with patients who have microsatellite-stable or proficient mismatch repair (pMMR) tumors. We examined MMR status as a predictor of adjuvant therapy benefit in patients with stages II and III colon cancer.

METHODS

MSI assay or immunohistochemistry for MMR proteins were performed on 457 patients who were previously randomly assigned to FU-based therapy (either FU + levamisole or FU + leucovorin; n = 229) versus no postsurgical treatment (n = 228). Data were subsequently pooled with data from a previous analysis. The primary end point was disease-free survival (DFS).

RESULTS

Overall, 70 (15%) of 457 patients exhibited dMMR. Adjuvant therapy significantly improved DFS (hazard ratio [HR], 0.67; 95% CI, 0.48 to 0.93; P = .02) in patients with pMMR tumors. Patients with dMMR tumors receiving FU had no improvement in DFS (HR, 1.10; 95% CI, 0.42 to 2.91; P = .85) compared with those randomly assigned to surgery alone. In the pooled data set of 1,027 patients (n = 165 with dMMR), these findings were maintained; in patients with stage II disease and with dMMR tumors, treatment was associated with reduced overall survival (HR, 2.95; 95% CI, 1.02 to 8.54; P = .04).

CONCLUSION

Patient stratification by MMR status may provide a more tailored approach to colon cancer adjuvant therapy. These data support MMR status assessment for patients being considered for FU therapy alone and consideration of MMR status in treatment decision making.

A review of the most promising biomarkers in colorectal cancer: one step closer to targeted therapy

Rapidly growing insights into the molecular biology of colorectal cancer (CRC) and recent developments in gene sequencing and molecular diagnostics have led to high expectations for the identification of molecular markers to be used in optimized and tailored treatment regimens. However, many of the published data on molecular biomarkers are contradictory in their findings and the current reality is that no molecular marker, other than the KRAS gene in the case of epidermal growth factor receptor (EGFR)- targeted therapy for metastatic disease, has made it into clinical practice. Many markers investigated suffer from technical shortcomings, resulting from lack of quantitative techniques to capture the impact of the molecular alteration. This understanding has recently led to the more comprehensive approaches of global gene expression profiling or genome-wide analysis to determine prognostic and predictive signatures in tumors. In this review, an update of the most recent data on promising biological prognostic and/or predictive markers, including microsatellite instability, epidermal growth factor receptor, KRAS, BRAF, CpG island methylator phenotype, cytotoxic T lymphocytes, forkhead box P3-positive T cells, receptor for hyaluronic acid-mediated motility, phosphatase and tensin homolog, and T-cell originated protein kinase, in patients with CRC is provided.

Microsatellite instability as a marker of prognosis and response to therapy: a meta-analysis of colorectal cancer survival data

BACKGROUND AND METHODS

We have reviewed and pooled data from published studies to evaluate the relationship between microsatellite instability (MSI) and colorectal cancer (CRC) prognosis. Thirty-one eligible studies reporting survival in 12782 patients characterised for MSI were pooled using a fixed- or random-effects model.

RESULTS

The summary odds ratio (OR) estimate for overall survival (OS) associated with MSI was 0.6 (95%CI 0.53-0.69, p<0.0001), with no evidence of heterogeneity. The effect was similar for disease-free survival (DFS) (OR=0.58, 95%CI 0.47-0.72, p<0.0001). In a subset of patients treated with 5-fluorouracil (5-FU)-based chemotherapy a significant improved prognosis was found for microsatellite stable (MSS) tumours (OR=0.52, 95%CI 0.4-0.6, p<0.0001) with no heterogeneity (p=0.53; I(2)=0%). By contrast a large heterogeneity characterised the data relative to 396 patients with MSI tumours (OR=0.69, 95%CI 0.3-1.5, p=0.1; heterogeneity: p=0.03; I(2)=58%).

CONCLUSIONS

This study confirmed the association between MSI and favourable prognosis as determined by both OS and DFS of CRC patients. A significant beneficial effect of 5-FU therapy was found for MSS tumours whilst no clear conclusion was reached for MSI tumours due to the high inter-study heterogeneity. We propose that this inconclusive result is due to the use of a single marker, such as MSI, that cannot account alone for the complexity of the mechanisms underlying 5-FU cytotoxicity. Future studies to predict response to 5-FU chemotherapy should include additional genome stability markers.

DNA mismatch repair and adjuvant chemotherapy in sporadic colon cancer

Defective DNA mismatch repair (MMR) occurs in approximately 15% of sporadic colorectal cancers (CRCs). Multiple retrospective studies have shown that patients with MMR-deficient CRCs have a more favorable stage-adjusted prognosis compared with those who have MMR-proficient tumors. Evidence also indicates that patients with MMR-deficient colon cancers do not benefit from treatment with adjuvant 5-fluorouracil chemotherapy. Furthermore, recent studies, including a pooled analysis, have validated the prognostic and predictive impact of MMR status in patients with stage II and III colon cancer who were treated in adjuvant chemotherapy trials. Given these data, it can be recommended that MMR status be determined and used to inform clinical decision-making for adjuvant chemotherapy in patients with stage II colon cancer.

Clinical relevance of microsatellite instability in colorectal cancer

Microsatellite instability (MSI) is a clonal change in the number of repeated DNA nucleotide units in microsatellites. It arises in tumors with deficient mismatch repair due to the inactivation of one of the four mismatch repair genes: MSH2, MLH1, MSH6, and PMS2. In order to determine the MSI status of a tumor, microdissection and polymerase chain reaction-based detection strategies are required. For practical purposes, MSI is equivalent to the loss of staining by immunohistochemistry (IHC) of one of the mismatch repair genes since both signify an abnormality in mismatch repair. Of all colorectal cancers (CRCs), 15% to 20% display MSI or abnormal IHC (often referred to as microsatellite instability [MIN] pathway). The remaining 80% to 85% of CRCs are microsatellite stable but most are characterized by chromosomal instability (CIN pathway). Almost all Lynch syndrome tumors have MSI or abnormal IHC and they account for up to one third of all MIN CRCs (3% to 5% of all CRCs). The remaining MIN tumors are sporadic as a result of somatic inactivation of the MLH1 gene caused by methylation of its promoter. Thus, the presence of a MSI/IHC abnormality prompts further investigations to diagnose Lynch syndrome, whereas its absence excludes Lynch syndrome. We recommend screening all CRC tumors for IHC or MSI. MIN tumors have a more favorable outcome than CIN tumors, and fluorouracil-based adjuvant chemotherapy does not improve the outcome of stage II or stage III MIN tumors. More data are needed to determine how best to treat patients with stage II and stage III MIN CRCs.

Defective mismatch repair as a predictive marker for lack of efficacy of fluorouracil-based adjuvant therapy in colon cancer

PURPOSE

Prior reports have indicated that patients with colon cancer who demonstrate high-level microsatellite instability (MSI-H) or defective DNA mismatch repair (dMMR) have improved survival and receive no benefit from fluorouracil (FU) -based adjuvant therapy compared with patients who have microsatellite-stable or proficient mismatch repair (pMMR) tumors. We examined MMR status as a predictor of adjuvant therapy benefit in patients with stages II and III colon cancer.

METHODS

MSI assay or immunohistochemistry for MMR proteins were performed on 457 patients who were previously randomly assigned to FU-based therapy (either FU + levamisole or FU + leucovorin; n = 229) versus no postsurgical treatment (n = 228). Data were subsequently pooled with data from a previous analysis. The primary end point was disease-free survival (DFS).

RESULTS

Overall, 70 (15%) of 457 patients exhibited dMMR. Adjuvant therapy significantly improved DFS (hazard ratio [HR], 0.67; 95% CI, 0.48 to 0.93; P = .02) in patients with pMMR tumors. Patients with dMMR tumors receiving FU had no improvement in DFS (HR, 1.10; 95% CI, 0.42 to 2.91; P = .85) compared with those randomly assigned to surgery alone. In the pooled data set of 1,027 patients (n = 165 with dMMR), these findings were maintained; in patients with stage II disease and with dMMR tumors, treatment was associated with reduced overall survival (HR, 2.95; 95% CI, 1.02 to 8.54; P = .04).

CONCLUSION

Patient stratification by MMR status may provide a more tailored approach to colon cancer adjuvant therapy. These data support MMR status assessment for patients being considered for FU therapy alone and consideration of MMR status in treatment decision making.

BRAF mutations, microsatellite instability status and cyclin D1 expression predict metastatic colorectal patients' outcome

Background:

The significance of BRAF mutations, microsatelite instability (MSI) status and cyclin D1 expression in patients with metastatic colorectal cancer (mCRC) was evaluated.

Methods:

Primary tumours from 144 patients treated for mCRC were assessed for BRAF (V600E) mutation, MSI status and cyclin D1. The data were correlated with progression-free survival (PFS) and overall survival (OS).

Results:

BRAF mutations were detected in 10 (out of 22, 45%) patients with MSI-H tumours compared with 2 (out of 122, 1.6%) in those with microsatellite stable tumours (P<0.001). The presence of BRAF mutations was correlated with cyclin D1 overexpression (7 out of 26 patients, 58% vs 5 out of 118 patients, 14% P=0.001). Patients with BRAF-mutated primary tumours had a significantly decreased PFS (2.7 vs 9.8 months; P<0.001) and median OS (14 vs 30 months; P<0.001) than patients with wild-type (wt) tumours. Patients with MSI-H and BRAF-mutated tumours experienced significantly lower PFS (3.1 vs 11.4 months; P=0.008) and OS (14.5 vs 35.5 months; P=0.004) than patients with MSI-H and BRAF wt tumours. Similarly, BRAF mutations and cyclin D1 overexpression were correlated with decreased PFS (3.1 vs 8.6 months; P=0.03) and OS (17.8 vs 39.2 months; P=0.01).

Conclusion:

BRAF V600E mutations are associated with MSI-H status and cyclin D1 overexpression and characterize a subgroup of patients with poor prognosis.

Thymidilate synthase expression predicts longer survival in patients with stage II colon cancer treated with 5-flurouracil independently of microsatellite instability

BACKGROUND

5-Fluorouracil (5-FU) is the most commonly used therapeutic agent for colon cancer treatment. Several studies have evaluated in patients with colon cancer, either the role of genes involved in the 5-FU pathway, such as thymidylate synthase (TS), thymidine phosphorylase (TP) and dihydropyrimidine dehydrogenase (DPD) or the role of microsatellite instability (MSI) as prognostic or predictive markers for adjuvant chemotherapy efficacy, with discordant results. In this study we investigated the combined effect of TS, TP, DPD mRNA expression and MSI status in primary tumors of patients with colon cancer, all treated with 5-FU adjuvant therapy.

METHODS

TS, TP and DPD expression levels were investigated by real-time quantitative RT-PCR on RNA extracts from formalin-fixed and paraffin-embedded tissues of 55 patients with colon adenocarcinoma. In the same case study MSI status was assessed on DNA extracts.

RESULTS

A higher TS expression was significantly associated with a longer survival for patients with cancers of stage II (P < 0.01), but not for those with stage III (P = 0.68). In addition, in multivariate analysis, a higher TS expression was significantly associated with a decreased risk of death (HR 0.13, 95% CI 0.03-0.59, P < 0.01), while the MSI status did not have effects on patients' survival.

CONCLUSIONS

This retrospective investigation suggests that TS gene expression at mRNA level can be a useful marker of better survival in patients (especially of those with cancers of stage II) receiving 5-FU adjuvant chemotherapy, independently of the MSI status.

Smoking, gender, and ethnicity predict somatic BRAF mutations in colorectal cancer

Approximately 5% to 15% of all colorectal cancers (CRC) have an activating BRAF somatic mutation, which may be associated with a distinct risk profile compared with tumors without BRAF mutations. Here, we measured the prevalence and epidemiologic correlates of the BRAF V600E somatic mutation in cases collected as a part of a population-based case-control study of CRC in northern Israel. The prevalence of BRAF V600E was 5.0% in this population, and the mutation was more likely to be found in tumors from cases who were of Ashkenazi Jewish descent [odds ratio (OR), 1.87; 95% confidence interval (95% CI), 1.01-3.47], female (OR, 1.97; P = 1.17-3.31), and older (73.8 years versus 70.3 years; P < 0.001). These results were similar when restricting to only tumors with microsatellite instability. Whether smoking was associated with a BRAF somatic mutation depended on gender. Although men were less likely to have a tumor with a BRAF somatic mutation, men who smoked were much more likely to have a tumor with a somatic BRAF mutation (OR(interaction), 4.95; 95% CI, 1.18-20.83) than women who never smoked. We note the strong heterogeneity in the reported prevalence of the BRAF V600E mutation in studies of different ethnicities, with a lower prevalence in Israel than other Western populations but a higher prevalence among Jewish than non-Jewish Israeli cases. Epidemiologic studies of CRC should incorporate somatic characteristics to fully appreciate risk factors for this disease.

Microsatellite instability in colorectal cancer-the stable evidence

Microsatellite instability (MSI) is the molecular fingerprint of a deficient mismatch repair system. Approximately 15% of colorectal cancers (CRC) display MSI owing either to epigenetic silencing of MLH1 or a germline mutation in one of the mismatch repair genes MLH1, MSH2, MSH6 or PMS2. Methods to detect MSI are well established and routinely incorporated into clinical practice. A clinical and molecular profile of MSI tumors has been described, leading to the concept of an MSI phenotype in CRC. Studies have confirmed that MSI tumors have a better prognosis than microsatellite stable CRC, but MSI cancers do not necessarily have the same response to the chemotherapeutic strategies used to treat microsatellite stable tumors. Specifically, stage II MSI tumors might not benefit from 5-fluorouracil-based adjuvant chemotherapy regimens. New data suggest possible advantages of irinotecan-based regimens, but these findings require further clarification. Characterization of the molecular basis of MSI in CRC is underway and initial results show that mutations in genes encoding kinases and candidate genes with microsatellite tracts are over-represented in MSI tumors. Transcriptome expression profiles of MSI tumors and systems biology approaches are providing the opportunity to develop targeted therapeutics for MSI CRC.

Value of the identification of microsatellite instability in colorectal cancer

OBJECTIVE

Recent studies defend a possible prognostic and therapeutic value of the identification of microsatellite instability (MSI) in colorectal cancer. This work tries to assess the impact that the identification of MSI tumours can have in clinical practice.

MATERIAL AND METHODS

We recovered tumour samples from 92 of the 143 patients operated on for colorectal cancer in our institution between 1995 and 2000. Five MSI markers (BAT 25, BAT 26, D2S123, D5S346 and D17S250) were studied on them. The rate and clinicopathologic characteristics of MSI tumours were investigated along with their impact on the global and disease-free survival as compared with microsatellite stable (MSS) tumours.

RESULTS

All 5 microsatellite markers' status were established in 73 patients (79.3% of the samples). Among them, 7 tumours showed instability in just one marker (low microsatellite instability [MSI-L]) whereas 5 tumours had mutations in 2 or more markers (high microsatellite instability [MSI-H]), for a total 15.4% rate of MSI tumours. All MSI-H tumours were located in the right colon. We could not fi nd any impact from MSI detection on global or disease-free survival.

CONCLUSIONS

MSI determination did not identify groups of patients with a different prognosis. Moreover, with such low incidence its determination can only be justified in those cases that fulfill Bethesda's criteria to identify families with Lynch's syndrome.

Locally advanced rectal cancer: from molecular profiling to clinical practice. A literature review: Part 2

Colorectal cancer is the third most common cause of cancer deaths worldwide. The management of rectal cancer has undergone, and continues to undergo, significant evolutions. In the last two decades, new multimodality strategies have been developed. The ability to predict tumor response before treatment could significantly impact the selection of patients for preoperative combined-modality therapy, as well as potentially modify postoperative treatment plans. The present review analyzes the new molecular targets that could be involved in predicting response and prognosis.

Overview of systemic therapy for colorectal cancer

Colorectal cancer (CRC) is the third most common cancer and second leading cause of death from cancer in North America. The authors provide an overview of the indications for both chemotherapy and targeted therapy, as well as discuss the efficacy and toxicity of systemic therapy. They highlight the key studies that lead to the initial historical use of fluorouracil (5FU) based chemotherapy in the adjuvant and metastatic setting, the recent adoption of 5FU plus leucovorin (LV) and oxaliplatin (FOLFOX) chemotherapy over 5FU when treating adjuvant patients, and the use of FOLFOX or 5FU plus LV and irinotecan (FOLFIRI) in metastatic patients. They also review the role of chemotherapy in treating rectal cancer and resectable liver metastatic disease. Future areas of research focus for systemic therapy of colorectal cancer are highlighted.

SelTarbase, a database of human mononucleotide-microsatellite mutations and their potential impact to tumorigenesis and immunology

About 15% of human colorectal cancers and, at varying degrees, other tumor entities as well as nearly all tumors related to Lynch syndrome are hallmarked by microsatellite instability (MSI) as a result of a defective mismatch repair system. The functional impact of resulting mutations depends on their genomic localization. Alterations within coding mononucleotide repeat tracts (MNRs) can lead to protein truncation and formation of neopeptides, whereas alterations within untranslated MNRs can alter transcription level or transcript stability. These mutations may provide selective advantage or disadvantage to affected cells. They may further concern the biology of microsatellite unstable cells, e.g. by generating immunogenic peptides induced by frameshifts mutations. The Selective Targets database (http://www.seltarbase.org) is a curated database of a growing number of public MNR mutation data in microsatellite unstable human tumors. Regression calculations for various MSI–H tumor entities indicating statistically deviant mutation frequencies predict TGFBR2, BAX, ACVR2A and others that are shown or highly suspected to be involved in MSI tumorigenesis. Many useful tools for further analyzing genomic DNA, derived wild-type and mutated cDNAs and peptides are integrated. A comprehensive database of all human coding, untranslated, non-coding RNA- and intronic MNRs (MNR_ensembl) is also included. Herewith, SelTarbase presents as a plenty instrument for MSI-carcinogenesis-related research, diagnostics and therapy.

SelTarbase, a database of human mononucleotide-microsatellite mutations and their potential impact to tumorigenesis and immunology

About 15% of human colorectal cancers and, at varying degrees, other tumor entities as well as nearly all tumors related to Lynch syndrome are hallmarked by microsatellite instability (MSI) as a result of a defective mismatch repair system. The functional impact of resulting mutations depends on their genomic localization. Alterations within coding mononucleotide repeat tracts (MNRs) can lead to protein truncation and formation of neopeptides, whereas alterations within untranslated MNRs can alter transcription level or transcript stability. These mutations may provide selective advantage or disadvantage to affected cells. They may further concern the biology of microsatellite unstable cells, e.g. by generating immunogenic peptides induced by frameshifts mutations. The Selective Targets database (http://www.seltarbase.org) is a curated database of a growing number of public MNR mutation data in microsatellite unstable human tumors. Regression calculations for various MSI-H tumor entities indicating statistically deviant mutation frequencies predict TGFBR2, BAX, ACVR2A and others that are shown or highly suspected to be involved in MSI tumorigenesis. Many useful tools for further analyzing genomic DNA, derived wild-type and mutated cDNAs and peptides are integrated. A comprehensive database of all human coding, untranslated, non-coding RNA- and intronic MNRs (MNR_ensembl) is also included. Herewith, SelTarbase presents as a plenty instrument for MSI-carcinogenesis-related research, diagnostics and therapy.

DNA mismatch repair (MMR)-dependent 5-fluorouracil cytotoxicity and the potential for new therapeutic targets

The metabolism and efficacy of 5-fluorouracil (FUra) and other fluorinated pyrimidine (FP) derivatives have been intensively investigated for over fifty years. FUra and its antimetabolites can be incorporated at RNA- and DNA-levels, with RNA level incorporation provoking toxic responses in human normal tissue, and DNA-level antimetabolite formation and incorporation believed primarily responsible for tumour-selective responses. Attempts to direct FUra into DNA-level antimetabolites, based on mechanism-of-action studies, have led to gradual improvements in tumour therapy. These include the use of leukovorin to stabilize the inhibitory thymidylate synthase-5-fluoro-2'-deoxyuridine 5' monophoshate (FdUMP)-5,10-methylene tetrahydrofolate (5,10-CH(2)FH(4)) trimeric complex. FUra incorporated into DNA also contributes to antitumour activity in preclinical and clinical studies. This review examines our current state of knowledge regarding the mechanistic aspects of FUra:Gua lesion detection by DNA mismatch repair (MMR) machinery that ultimately results in lethality. MMR-dependent direct cell death signalling or futile cycle responses will be discussed. As 10-30% of sporadic colon and endometrial tumours display MMR defects as a result of human MutL homologue-1 (hMLH1) promoter hypermethylation, we discuss the use and manipulation of the hypomethylating agent, 5-fluorodeoxycytidine (FdCyd), and our ability to manipulate its metabolism using the cytidine or deoxycytidylate (dCMP) deaminase inhibitors, tetrahydrouridine or deoxytetrahydrouridine, respectively, as a method for re-expression of hMLH1 and re-sensitization of tumours to FP therapy.

Clinical implications of microsatellite instability in sporadic colon cancers

PURPOSE OF REVIEW

To review data demonstrating the prognostic and predictive impact of microsatellite instability (MSI) in human colon carcinomas.

RECENT FINDINGS

MSI is a molecular marker of defective DNA mismatch repair that is detected in approximately 15% of sporadic colon cancers. Most, but not all retrospective studies, have shown that colon cancers with MSI have better stage-adjusted survival rates compared with non-MSI tumors. Furthermore, analyses of colon cancers from participants in randomized adjuvant therapy trials have suggested that MSI tumors do not benefit from treatment with 5-fluorouracil. Recent studies, including a pooled analysis, validate prior data demonstrating the prognostic and predictive impact of MSI status in colon cancer.

SUMMARY

MSI is a molecular marker that can provide valuable prognostic and predictive information in colon cancer patients. In the appropriate clinical setting, MSI data can be used in clinical decision-making. Specifically, the favorable outcome of stage II colon cancers with MSI indicates that such patients should not receive adjuvant chemotherapy. Although data for stage III colon cancers with MSI suggest a lack of benefit from 5-fluorouracil alone, the benefit of the current standard treatment, 5-fluorouracil, leucovorin, and oxaliplatin, in this subgroup remains unknown and awaits further study.

Does microsatellite instability predict the efficacy of adjuvant chemotherapy in colorectal cancer? A systematic review with meta-analysis

BACKGROUND

Microsatellite instability (MSI) status in predicting the efficacy of adjuvant chemotherapy in colorectal cancer remains controversial.

MATERIALS AND METHODS

Studies were identified through PubMed, Embase and ASCO proceedings with a combination of keywords (colorectal cancer, chemotherapy and MSI).

RESULTS

A MA was performed for treated and non-treated MSI population on seven studies. Statistical calculations were performed on 7 studies representing 3690 patients; mean age: 65.5 years; 810 stage II and 2444 stage III (75%). MSI-high (MSI-H) was found in 454 patients (14% of the global population), and microsatellite stable (MSS) in 2871. A total of 1444 patients received 5-fluorouracil (5FU)-based chemotherapy, whereas 1518 patients did not. For MSI-H patients, there was no statistically significant difference for RFS whether or not they received chemotherapy (5 studies); HR RFS: 0.96 (95% confidence interval (CI): 0.62-1.49); HR OS (6 studies): 0.70 (95% CI: 0.44-1.09; p=0.12). Elsewhere, we found a significant interaction between MSI status (MSI-H or MSS) and therapeutic status suggesting a lesser benefit for MSI-H than for MSS patients (HR interaction RFS: 0.77 (95% CI: 0.67-0.87)).

CONCLUSION

We found similar RFS for treated and untreated MSI-H patients, showing that MSI-H status, in addition to being a good prognostic factor is also a predictive factor of non response.

Participation of DNA repair in the response to 5-fluorouracil

The anti-metabolite 5-fluorouracil (5-FU) is employed clinically to manage solid tumors including colorectal and breast cancer. Intracellular metabolites of 5-FU can exert cytotoxic effects via inhibition of thymidylate synthetase, or through incorporation into RNA and DNA, events that ultimately activate apoptosis. In this review, we cover the current data implicating DNA repair processes in cellular responsiveness to 5-FU treatment. Evidence points to roles for base excision repair (BER) and mismatch repair (MMR). However, mechanistic details remain unexplained, and other pathways have not been exhaustively interrogated. Homologous recombination is of particular interest, because it resolves unrepaired DNA intermediates not properly dealt with by BER or MMR. Furthermore, crosstalk among DNA repair pathways and S-phase checkpoint signaling has not been examined. Ongoing efforts aim to design approaches and reagents that (i) approximate repair capacity and (ii) mediate strategic regulation of DNA repair in order to improve the efficacy of current anticancer treatments.

Restoring TGFbeta function in microsatellite unstable (MSI-H) colorectal cancer reduces tumourigenicity but increases metastasis formation

BACKGROUND

TGFbeta is an important cell growth regulator which may have a role in metastasis formation. Microsatellite unstable (MSI-H) colon cancer serves as a unique model to demonstrate this as most MSI-H colon cancers have a mutation in the transforming growth factor beta receptor II (TGFbetaRII) gene and a low metastatic rate.

AIMS

To demonstrate an increase in invasion and metastasis in a MSI-H colorectal cancer cell line with a known mutation in TGFbetaRII.

MATERIALS AND METHODS

By restoring the wild-type TGFbetaRII gene in the KM12C MSI-H colorectal carcinoma cell line with a known mutation in TGFbetaRII, we have demonstrated that both invasion and metastasis in this cell line was significantly increased. A mouse metastatic model have shown that liver metastases were increased in mice inoculated with cells containing a wild-type TGFbetaRII gene (42% for the transfected group compared with 15% for the control group; p = 0.0379), despite a reduction in the size of primary tumours.

CONCLUSIONS

This study highlights an important mechanism which may contribute to the low metastatic rate of MSI-H colon cancers and demonstrates the importance of TGFbeta signalling in metastasis formation. Previous studies involving breast cancer cell lines have shown that blocking TGFbeta signalling results in a reduction in metastasis formation. This study is the first study to use a cell line with a low metastatic rate and TGFbetaRII mutations to demonstrate that restoring TGFbeta signalling increases the metastatic rate.

Microsatellite instability in colorectal cancer and association with thymidylate synthase and dihydropyrimidine dehydrogenase expression

Background

Microsatellite instability (MSI) refers to mutations in short motifs of tandemly repeated nucleotides resulting from replication errors and deficient mismatch repair (MMR). Colorectal cancer with MSI has characteristic biology and chemosensitivity, however the molecular basis remains unclarified. The association of MSI and MMR status with outcome and with thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) expression in colorectal cancer were evaluated.

Methods

MSI in five reference loci, MMR enzymes (hMSH2, hMSH6, hMLH1 and hPMS2), thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) expression were assessed in paraffin embedded tumor specimens, and associated with outcome in 340 consecutive patients completely resected for colorectal cancer stages II-IV and subsequently receiving adjuvant 5-fluorouracil therapy.

Results

MSI was found in 43 (13.8%) tumors. Absence of repair protein expression was assessed in 52 (17.0%) tumors, which had primarily lost hMLH1 in 39 (12.7%), hMSH2 in 5 (1.6%), and hMSH6 in 8 (2.6%) tumors. In multivariate analysis MSI (instable) compared to MSS (stable) tumors were significantly associated with lower risk of recurrence (hazard ratio (HR) = 0.3; 95% CI: 0.2–0.7; P = 0.0007) and death (HR = 0.4; 95% CI: 0.2–0.9; P = 0.02) independently of the TS and DPD expressions. A direct relationship between MSI and TS intensity (P = 0.001) was found, while there was no significant association with DPD intensity (P = 0.1).

Conclusion

The favourable outcome of MSI colorectal carcinomas is ascribed mainly to the tumor biology and to a lesser extent to antitumor response to 5-fluorouracil therapy. There is no evidence that differential TS or DPD expression may account for these outcome characteristics.

Predicting clinical outcome of 5-fluorouracil-based chemotherapy for colon cancer patients: is the CpG island methylator phenotype the 5-fluorouracil-responsive subgroup?

The CpG island methylator phenotype (CIMP+) of colorectal cancer (CRC) occurs predominantly in the proximal colon and is characterized by frequent hypermethylation of gene promoter regions. In this review, we present evidence suggesting CIMP+ represents the subgroup of colon cancers that are responsive to 5-fluorouracil (5-FU)-based treatments. CIMP+ has been associated with survival benefit from 5-FU in a clinical study of CRC, with additional evidence coming from studies on gastric cancer and tumor cell lines. Elevated concentrations of 5-10-methylene tetrahydrofolate (CH(2)FH(4)) occur in CIMP+ tumors and are probably due to low expression levels for gamma-glutamyl hydrolase (GGH). Clinical and in vitro work has previously shown that high CH(2)FH(4) and low GGH expression levels correlate with good response to 5-FU. Methylation-induced silencing of dihydropyrimidine dehydrogenase, the rate-limiting enzyme in 5-FU degradation, may also provide a link between CIMP+ and good response to 5-FU. The CIMP+-related phenotype referred to as microsatellite instability (MSI+) has been widely investigated as a predictive marker of response to 5-FU, with contradictory results. The interpretation of these studies is likely to be confounded by the fact that some MSI+ tumors occur in the background of CIMP+, but a significant proportion of others do not. Further studies on tumors from randomized clinical trials are required to confirm the value of CIMP+ and associated molecular features for the prediction of clinical outcome to 5-FU-based chemotherapy.

Thymidylate synthase and microsatellite instability in colorectal cancer: implications for disease free survival, treatment response and survival with metastases

BACKGROUND

Colorectal cancer (CRC) cell lines displaying microsatellite instability (MSI) are resistant to 5-fluorouracil (5-FU) in vitro, which can be overcome by restoring DNA mismatch repair (MMR) competence. Thymidylate synthase (TS) is inhibited by 5-FU, being another potential mediator of therapeutic resistance to 5-FU. The clinical relevance of these observations remains unclear.

OBJECTIVE

We examined the expression of TS and two MMR proteins (hMLH1 and hMSH2) in advanced CRC patients, to determine a) their mutual relationship, b) association to therapeutic response and c) impact on disease outcome.

MATERIAL AND METHODS

Tumour samples from 73 patients CRC who were treated in advanced stage with either irinotecan alone or in combination with 5-FU/leucovorin, were analysed for expression of TS, hMLH1 and hMSH2 using immunohistochemistry (IHC).

RESULTS

TS expression was closely correlated with hMLH1 expression (negative-weak/moderate-strong) (p=0.0001). TS-MMR expression was significantly (p=0.029 for whole series; p=0.004 for the 5-FU treated cases) related to response to treatment; tumours with low levels of both TS and MMR responded better (n=14/27, 51.8%) than those with high TS and MMR (n=3/18, 16.6%). Patients with high TS-MMR expression had a significantly longer DFS (47 months vs. 9 months, n=26) than those with low TS-MMR index (p=0.015), while the reverse was true concerning survival with metastases (WMS) (p=0.018) in all the patients (n=73).

CONCLUSIONS

The present data suggest that MSI patients with low TS and deficient MMR demonstrate a significantly shorter DFS and longer WMS than patients with high expression of both markers, and they are also more likely to obtain the greatest benefit from 5-FU based chemotherapy.

Predictive and prognostic value of microsatellite instability in patients with advanced colorectal cancer treated with a fluoropyrimidine and oxaliplatin containing first-line chemotherapy. A report of the AIO Colorectal Study Group

BACKGROUND AND AIMS

Microsatellite instability (MSI) is a potential indicator of prognosis in patients with colorectal cancer (CRC). To date, there are a limited number of studies which investigated its role in advanced CRC. Our study investigated the value of high degree of MSI (MSI-H) in patients treated with 5-FU/oxaliplatin-based chemotherapy which has been done by only one further study recently.

PATIENTS AND METHODS

In this study, we investigated tumour tissues from 108 patients with metastatic CRC who were treated in a prospective, randomised trial comparing two oxaliplatin and 5-FU-based therapy regimens (FUFOX vs. CAPOX) involving a total of 474 patients. We determined the incidence and prognostic value of a high degree of microsatellite instability. The specimens were analysed by PCR corresponding to the National Institute of Health reference panel. In addition, immunostaining of the mismatch repair proteins MLH1, MSH2 and MSH6 was performed.

RESULTS AND FINDINGS

The incidence of MSI-H was 4%. MSI-H was correlated with a lower rate of disease control compared to non-MSI-H patients (p = 0.02). However, there was no correlation between MSI-H and progression-free survival or overall survival.

INTERPRETATION AND CONCLUSION

MSI-H incidence in metastatic CRC was low. Our data suggest that MSI-H may be correlated with a poorer response to a 5-FU/oxaliplatin treatment. This finding needs confirmation in a larger cohort.

The efficacy of adjuvant chemotherapy with 5-fluorouracil in colorectal cancer depends on the mismatch repair status

AIMS

The aim of this study is to evaluate if mismatch repair (MMR) defective colorectal cancer has a different response to adjuvant 5-fluorouracil (5-FU) chemotherapy in a cohort of patients prospectively followed during 5 years.

METHODS

The cohort included 754 surgically treated patients with colorectal cancer. MMR status was diagnosed by MLH1 and MSH2 immunohistochemistry and microsatellite instability analysis. Median follow-up was 49.2 months (range 1-73). At inclusion, 505 patients were diagnosed as TNM II or III stage, analysis of the efficacy of adjuvant chemotherapy was made on this population. Adjuvant chemotherapy was applied to 248 patients (98.2% 5-FU based).

RESULTS

MMR deficiency was found in 76 patients (10.1%). No differences were found in overall survival (log-rank p=0.3) or disease-free survival (log-rank p=0.3) regarding MMR status. Adjuvant chemotherapy improves survival in patients in the II or III stage, but this improvement is only evident in patients with MMR-competent tumours (log-rank p=0.00001). Survival of patients with MMR-defective tumours does not improve with adjuvant chemotherapy (log-rank p=0.7). A multivariate analysis showed an independent effect of the interaction between MMR status and adjuvant chemotherapy (Hazard ratio 2.04; 95% confidence interval: 1.42-2.93).

CONCLUSION

In a cohort of colorectal cancer patients, those with MMR-deficient tumours seem not to benefit from 5-FU-based chemotherapy.

Up-regulation of the hypoxia-inducible factor-1 transcriptional pathway in colorectal carcinomas

The aim of the study was to identify the impact on prognosis of hypoxia-inducible factor-1 genetic program in colorectal carcinomas and to develop an experimental procedure that would allow a reliable quantitative gene expression analysis in formalin-fixed and paraffin-embedded tissue. The expression of hypoxia-inducible factor-1alpha and 13 hypoxia-inducible factor-1 target genes (AMF, CAIX, VEGF, VEGFR1, VEGFR2, HGF, MET, TGFalpha, EGFR, IGF2, MMP2, PLAUR, NIX) was quantified by real-time polymerase chain reaction in 18 colorectal, poorly differentiated neuroendocrine carcinomas and in 60 invasive colorectal carcinomas. Moreover, hypoxia-inducible factor-1alpha protein expression was evaluated by immunohistochemistry. High levels of hypoxia-inducible factor-1alpha were positively associated with poorly differentiated neuroendocrine carcinoma histology (P < .005), poor differentiation (P < .025), presence of necrosis, and presence of microsatellite instability (P < .05). AMF, TGFalpha, IGF2, NIX, VEGF, and VEGFR2 transcripts were significantly higher in the very aggressive poorly differentiated neuroendocrine carcinomas than in exocrine colorectal carcinomas and TGFalpha expression was significantly associated with presence of lymph nodal metastases (P < .05). High levels of TGFalpha and NIX were significantly associated with decreased overall survival (P < .001; P < .01). The multivariate analysis showed that advanced stage, presence of lymph node metastases, and high TGFalpha expression had an independent effect on survival (P < .006; P < .01; P < .0006). Our study suggests an up-regulation of the hypoxia-inducible factor-1 transcriptional pathway in colorectal carcinomas. hypoxia-inducible factor-1alpha overexpression alone, has no impact on the prognosis of colorectal carcinomas likely because the consequences of hypoxia-inducible factor-1alpha expression/stabilization strongly depend on the genetic background of the transformed cells. Mechanisms leading to increased synthesis of hypoxia-inducible factor-1alpha mRNA via autocrine growth factor loops may play a crucial role in invasive growth in this site.

Lumboaortic and iliac lymphadenectomy for lymph node recurrence of colorectal cancer: prognostic value of the MSI phenotype

BACKGROUND

Some patients have isolated lumboaortic and/or iliac lymph node recurrences (ILNR) of colorectal cancer. Current guidelines recommend the use of chemotherapy. The aim of our study was to assess the carcinological results of lymphadenectomy for ILNR and to identify prognostic factors that may be used to select patients for this aggressive surgical approach.

METHODS

Medical notes, pathological findings, and surgical procedure of patients who underwent lymphadenectomy for ILNR of colorectal cancer between 1998 and 2005 were reviewed.

RESULTS

Ten patients (four women) underwent lymphadenectomy for ILNR. Lymphadenectomy was performed after a mean of 37 +/- 16.6 months after colon or rectal resection. Two patients developed a postoperative complication. Mean number of lymph nodes removed was 5.7 +/- 3.3. After a median follow-up of 30.7 months, four patients were alive, including two patients without recurrence at 95 and 96 months after colectomy and two with local and distant recurrences at 114 and 70 months. Among the three patients with microsatellite-unstable (MSI) tumors, two were free of disease at 61 and 81 months, respectively, and one died of recurrent disease 20 months after lymphadenectomy.

CONCLUSION

Lymphadenectomy for ILNR of colorectal cancer is a feasible therapeutic option for selected patients. These preliminary results suggest that resection should be proposed for MSI patients because cure is possible, but to be confirmed, the findings require larger studies.

Increased TGF-beta 1 protein expression in patients with advanced colorectal cancer

INTRODUCTION

There is evidence that TGF-beta 1 plays a role as a tumor suppressor in early disease and has pro-oncogenic effects in advanced tumor stage. The aim of the study was to correlate TGF-beta 1 in plasma and tissue to clinical and pathological parameters in patients with various stages of disease progression.

METHODS

One hundred sixty-nine patients who underwent surgery for a colorectal carcinoma were prospectively included. Blood samples, tumor free mucosa and tumor biopsies were assayed.

RESULTS

TGF-beta 1 protein expression in tumors increased with increasing T-stage regardless of whether patients with metastatic disease were included or not (P = 0.0006). Patients with metastatic disease showed elevated TGF-beta 1 protein expression in both tumor tissue (P = 0.004) and plasma (P = 0.001) compared to those without metastatic disease. TGF-beta 1 protein expression was higher in the colon compared with the rectum in both tumor tissue and tumor-free bowel (P = 0.03), regardless of whether patients with metastatic disease were included or not. This difference was mainly attributable to a higher TGF-beta 1 protein expression in non-metastatic patients with lymph node positivity (P = 0.005).

CONCLUSIONS

Higher TGF-beta 1 protein expression is associated with increasing T-stage and metastatic disease, indicating that TGF-beta 1 is of importance in tumor progression. The localization of the tumor seems to influence the TGF-beta 1 protein expression in patients with tumor cell-positive lymph nodes.

Poorly differentiated colorectal adenocarcinomas show higher rates of microsatellite instability and promoter methylation of p16 and hMLH1: a study matched for T classification and tumor location

BACKGROUND

Extensive genetic and epigenetic analysis of poorly differentiated colorectal adenocarcinomas (Por) has been difficult, as the number of cases is too small.

METHODS

We investigated genetic and epigenetic alterations of 53 cases of Por and 53 cases of well-differentiated colorectal adenocarcinomas (WD) to clarify their differences. The cases of WD were matched with the cases of Por for T classification and tumor location, which influence genetic and epigenetic alterations. We evaluated microsatellite instability (MSI) status and loss of heterozygosity (LOH) of four loci (2p, 5q, 17p, 18q), and defined "MSI tumors" as those that showed MSI-H, and "chromosomal instability (CIN) tumors" as those that showed LOH but not MSI-H. Further, we evaluated the methylation status of the hMLH1 and p16 promoter region.

RESULTS

MSI tumors were significantly more frequent in Por (22.6%) than in WD (3.8%; P = 0.0041). CIN tumors were significantly less frequent in Por (64.2%) than in WD (83.0%; P = 0.046). Further, methylation of the p16 and hMLH1 promoter region was significantly more frequent in Por than in WD (P = 0.037, P = 0.047, respectively).

CONCLUSIONS

Our results indicate that Por tumorigenesis strongly correlates with MSI and methylation of the p16 and hMLH1 promoter region.

Differences between right- and left-sided colon cancer in patient characteristics, cancer morphology and histology

BACKGROUND AND AIM

Recently, the clinical and biological differences between right- and left-sided colon cancers have been widely debated. However, close analyses of these clinical differences, based on large-scale studies, have been scarcely reported.

METHODS

A total of 3552 consecutive Japanese colorectal cancer cases were examined and the clinical differences between right- and left-sided colon cancer cases were investigated.

RESULTS

The proportion of right-sided colon cancer was relatively high in patients aged less than 40 years (33%) and more than 80 years (43%). The proportion of right-sided colon cancer in patients aged 40-59 years was relatively low (male 22% and female 29%). In male patients the proportion increased in the 70-79 years age group (30%), while in female patients the proportion increased in the 60-69 years age group (39%). Right-sided colon cancer was more likely to be detected at an advanced stage (T1 stage; left 22%, right 15%) (P < 0.01) with severe symptoms. Polypoid-type early cancer was dominant in the left colon (left 59%; right 40%) (P < 0.01), while the proportion of flat-type early cancer in the right colon was significantly higher than that in the left colon (left 25%; right 44%) (P < 0.01).

CONCLUSIONS

Specific age distribution of right-sided colon cancer was observed and the difference between male and female patients was highlighted. Other clinical features also differed between right- and left-sided colon cancer, suggesting that different mechanisms may be at work during right and left colon carcinogenesis.

Detection of hMSH2 and hMLH1 mutations in Chinese hereditary non-polyposis colorectal cancer kindreds

AIM: To establish and validate the mutation testing for identification and characterization of hereditary non-polyposis colorectal cancer (HNPCC) in suspected Chinese patients.

METHODS: Five independent Chinese kindreds with HNPCC fulfilling the classical Amsterdam criteria were collected. Genomic DNA was extracted after informed consent was obtained. The coding region of hMSH2 and hMLH1 genes was detected by polymerase chain reaction (PCR) and denaturing high-performance liquid chromatography (DHPLC). Mutations identified in the proband by DHPLC were directly sequenced using a 377 DNA sequencer, analyzed with a basic local alignment tool (BLAST), and tested in the corresponding family members by direct DNA sequencing.

RESULTS: Mutations were identified in two Chinese HNPCC kindreds. One was the missense mutation of hMSH2 c.1808A→G resulting in Asp 603 Gly identified in the proband of the fifth HNPCC (HNPCC5) kindred. In the HNP5 kindred, three family members were found to have this mutation and two of them had colorectal cancer. The other mutation of hMLH1 c.1882A→G was identified in the HNP2 kindred’s proband, which might be the nonsense mutation analyzed by BLAST.

CONCLUSION: Pedigree investigation and mutation testing of hMSH2 and hMLH1 are the practical methods to identify high-risk HNPCC patients in China.

Molecular classification and correlates in colorectal cancer

Molecular classification of colorectal cancer is evolving. As our understanding of colorectal carcinogenesis improves, we are incorporating new knowledge into the classification system. In particular, global genomic status [microsatellite instability (MSI) status and chromosomal instability (CIN) status] and epigenomic status [CpG island methylator phenotype (CIMP) status] play a significant role in determining clinical, pathological and biological characteristics of colorectal cancer. In this review, we discuss molecular classification and molecular correlates based on MSI status and CIMP status in colorectal cancer. Studying molecular correlates is important in cancer research because it can 1) provide clues to pathogenesis, 2) propose or support the existence of a new molecular subtype, 3) alert investigators to be aware of potential confounding factors in association studies, and 4) suggest surrogate markers in clinical or research settings.

5-Fluorouracil is efficiently removed from DNA by the base excision and mismatch repair systems

BACKGROUND & AIMS

5-Fluorouracil (FU) is one of the mainstays of colon cancer chemotherapy. Although developed as an inhibitor of thymidylate synthase, its cytotoxicity has been linked also to its incorporation into RNA. Surprisingly, although FU is incorporated also into DNA, little is known about its metabolism in this nucleic acid.

METHODS

Using extracts of human cells and circular DNA substrates containing a single FU residue either paired with adenine or mispaired with guanine, we studied the enzymology of FU processing.

RESULTS

In nicked circular substrates, FU/G mispairs were efficiently repaired by mismatch repair (MMR). In covalently closed circular DNA, which is refractory to MMR, FU/G repair was initiated by either thymine-DNA glycosylase or uracil-DNA glycosylase, whereas FU/A pairs were processed by UNG. Methylated CpG binding domain 4 protein and single-strand selective monofunctional uracil-DNA glycosylase 1 did not detectably contribute to FU removal; however, because these recombinant enzymes process FU/G and FU/A in oligonucleotide substrates, respectively, they too may be involved in FU metabolism in vivo.

CONCLUSIONS

The functional redundancy of MMR and DNA glycosylases in FU processing should ensure that the drug is efficiently removed from DNA before it can interfere with essential DNA metabolic processes, such as transcription. However, in FU-treated cells, the nucleotide pools are depleted of thymine. The repair synthesis might thus be inhibited and leave cytotoxic gaps or breaks in DNA. Moreover, FU and/or 5-fluorouracil-2'-deoxyuridine-5'-triphosphate removed from DNA will increase the intracellular concentration of the drug and thus exacerbate its cytotoxicity.

Importance of MutL homologue MLH1 and MutS homologue MSH2 expression in Turkish patients with sporadic colorectal cancer

AIM: To assess the incidence of MLH1 (the human MutL homologue) and MSH2 (the human MutS homologue) protein expression in Turkish patients with sporadic colorectal cancers and to compare their survival and clinicopathological features.

METHODS: We validated the tissue microarray technology in 77 colorectal carcinomas by analyzing the immunohistochemical expression of proteins involved in two main pathways of colorectal carcinogenesis: p53 protein for loss of heterozygosity tumors; MLH1 and MSH2 proteins for microsatellite instability (MSI).

RESULTS: Our analysis showed that 29 (39.2%) had loss of MLH1 expression, 5 (6.8%) had loss of MSH2 expression and 2 cases had loss of expression of both proteins. We found that 60% of MSH2-negative tumors were located in the right side of the colon; all MSH2-negative cases were women. In addition, the loss of MSH2 expression was correlated with low p53 expression. Neither MLH1 nor MSH2 expressions were associated with prognosis, although there seemed a tendency of longer survival (71.7 ± 8.65 mo vs 47.08 ± 5.26 mo) for the patients with MLH1-negative versus MLH1-positive carcinomas. There were not significant differences in overall and recurrence-free survival among MLH1/MSH2-positive and -negative cases.

CONCLUSION: Our data supports that Turkish patients with MLH1- and MSH2-defective tumors have some distinct features from each other. Although prognostic importance remains controversial, immunohistochemical analysis of mismatch repair genes may be used as a routine histopathological examination of sporadic colorectal carcinomas.

Microsatellite instability in poorly differentiated adenocarcinomas of the colon and rectum: relationship to clinicopathological features

BACKGROUND

Poorly differentiated adenocarcinomas of the colon and rectum (Por) feature the worst prognosis among the various types of colorectal carcinomas. Por is highly associated with microsatellite instability (MSI), although MSI is associated with an improved prognosis in colorectal cancers.

AIM

To investigate the influence of MSI on clinicopathological features and survival of patients affected by Por.

METHODS

53 patients affected by Por were investigated. DNA extracted from tumour sections and the corresponding normal tissue was analysed by PCR at five microsatellite loci: BAT25, BAT26, D2S123, D5S346 and D17S250. Tumours with alterations at two or more loci were classified as MSI-Por. The others were classified as microsatellite stability (MSS)-Por. The clinicopathological features and survival of patients with MSI-Por and MSS-Por were investigated.

RESULTS

Of the 53 patients who were examined, 12 (22.6%) were MSI-Por, whereas 41 (77.4%) were MSS-Por. Significant differences were found between MSI-Por and MSS-Por regarding the following clinicopathological features: age, gender, lymph-node metastasis (MSI-Por: 4/12; MSS-Por: 33/41), TNM stage (MSI-Por: T1/T2/T3/T4 = 2/6/2/2; MSS-Por: 3/3/19/16) and lymphatic invasion (MSI-Por: 4/10; MSS-Por: 27/35). Kaplan-Meier survival curves and log-rank analysis showed that MSI-Por was associated with better prognosis than MSS-Por, although no significant difference was found.

CONCLUSIONS

Compared with MSS-Por, MSI-Por is significantly associated with a low incidence of lymph-node metastases and a low stage. This indicates that MSI-Por is a less aggressive subtype.

The role of chemotherapy in microsatellite unstable (MSI-H) colorectal cancer

INTRODUCTION

High-frequency microsatellite instability (MSI-H) is an alternate pathway of colorectal carcinogenesis, which accounts for 15% of all sporadic colorectal cancers. These tumours arise from mutations in the DNA mismatch repair system and thus have different responses to chemotherapeutic agents compared to microsatellite stable (MSS) cancers.

OBJECTIVE

This review aims to summarise the available literature on the responses to chemotherapy in MSI-H colorectal cancer (CRC).

RESULTS AND DISCUSSION

5 Fluorouracil (5FU) is commonly used as a chemotherapeutic agent in colon cancer and in vitro evidence shows reduced response to 5FU in MSI-H CRC. The clinical evidence is conflicting but favours a reduced response to 5FU in MSI-H CRC. Several newer agents such as COX-2 inhibitors and irinotecan are also reviewed.

CONCLUSION

Available evidence suggests that MSI-H CRC have different behaviour patterns and response to chemotherapy compared with MSS CRC.

Molecular markers that predict response to colon cancer therapy

Progress in the treatment of colon cancer depends on the development of target-based molecules built on an improved understanding of the molecular biology of the disease. Defining end points for chemotherapy resistance is needed as drug resistance develops quickly and patients demonstrate variation in response to chemotherapy. Many techniques that measure a marker's preponderance have been developed including biochemical, immunohistochemical, genomics, proteomics or a combination thereof. However, standardization of these techniques that measure either genes or their protein products is urgently needed. This article reviews several markers (TS,TP, DPD, FT, EGFR, VEGF, CD44v6, TRAIL, microsatellite instability, allelic deletions, oncogenes and suppressor genes [c-myc, Ki-Ras, p53, p21, Topo I, Topo IIalpha, Fos, hMLH1, Bcl-2/Bax and MDR1], MDR-related proteins [Pgp, MRP and LRP], genomic polymorphisms [XPD, ERCC1, GSTP1 and TS 3 -UTR] and COX-;2) that influence DNA metabolism, DNA damage, programmed cell death, the immune or vascular system, or lead to mutations. When combined together and tested by newly developed genomic and proteomic approaches, many of these markers provide a more sensitive indicative predictor of response than when evaluated separately or by older biochemical, immunohistologic or morphologic methods. A global approach involving the simultaneous testing of several predictive multimarkers will provide critical information for improving chemotherapy to alleviate suffering from this disease.

Microsatellite instability did not predict individual survival of unselected patients with colorectal cancer

INTRODUCTION

High microsatellite instability (MSI-H) occurs in about 15% of colorectal cancers (CRC) and clinical as well as pathological features differ from tumours exhibiting low microsatellite instability (MSI-L) or microsatellite stability (MSS). Conflicting data exists about the relevance of MSI in predicting the prognosis and benefit of 5-fluorouracil (5-FU) based chemotherapy in patients with CRC. We investigated the usefulness of MSI as a predictor of distinct clinical attributes influencing recurrence rate and disease-free survival (DFS) subject to the use of adjuvant or palliative chemotherapy with 5-FU in stage II- stage IV CRC.

METHODS

We collected data and tumours of 416 consecutive stage I to IV CRC patients from 2000 to 2002, and followed them for a median time of 33 months. Microsatellite loci recommended by the National Cancer Institute were analysed. Cox proportional hazard modelling was used to compare clinical data and survival as well as associations for MSI and 5-FU treatment status of patients with MSI-H, MSI-L or MSS CRC.

RESULTS

We identified 52 MSI-H (13%), 21 MSI-L (5%) and 343 MSS (82%) tumours. CRC with MSI-H tended to have a decreased likelihood of metastasising to regional lymph nodes (p=0.055), whilst age of diagnosis and tumour location did not differ. In an analysis that did not take into account the use of chemotherapy, univariate and multivariate analyses failed to show a difference between MSI-H and MSS groups with respect to disease-free and overall survival. Furthermore, survival under application of 5-FU did not correlate with MSI status.

CONCLUSION

No clear influence of MSI status on overall survival and response to 5-FU chemotherapy was found.