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

Predicting chemotherapeutic response and toxicity in colorectal cancer

SUMMARY While treatment for colorectal cancer has evolved significantly over the past 10 years with the introduction of active chemotherapeutic agents and targeted therapies, this has been at the cost of increased toxicity for patients; and significant financial burden for governments and patients. Predicting clinical outcomes, especially given the largely elderly patient population involved, is therefore paramount. This review seeks to summarize existing data regarding the prediction of response and toxicity to chemotherapy agents currently used in the treatment of colorectal cancer.

Role of microsatellite instability in the management of colorectal cancers

Microsatellite instability is the consequence of a deficient mismatch repair system. It has a key role in the diagnostic strategy of Lynch syndrome, where tumours are all characterized by the presence of this phenotype. Microsatellite instability is therefore essential in the selection of colorectal cancer patients in whom a germline analysis of Mismatch Repair genes is possibly indicated. Moreover, microsatellite instability tumours are associated with a good prognosis and a resistance to fluorouracil-based adjuvant chemotherapy, which has a clinical application mainly in stage II colon cancer patients in whom adjuvant chemotherapy has a less beneficial effect than in stage III and outcome in presence of microsatellite instability is excellent. Recent data suggest that impact of microsatellite instability on benefit to fluorouracil-based adjuvant chemotherapy is dependent of the molecular mechanism involved in this genetic instability since an improved survival has been reported with adjuvant fluorouracil in microsatellite instability colorectal cancers of germline origin but not in sporadic cases. Predictive value of microsatellite instability on response to fluorouracil/oxaliplatin adjuvant chemotherapy has been less evaluated but recent studies suggest that the favorable outcome of Microsatellite instability tumours is maintained in patients receiving FOLFOX.

Adjuvant therapy in patients with stage II and III colon cancer under 70 years of age

SUMMARY Colorectal cancer is a common malignancy and its prognosis has improved over recent decades due to sustained efforts of the scientific community. This review focuses on adjuvant therapy across the lifespan of patients under 70 years of age. Here, we discuss the standard management of patients with stage III colon cancer, consisting of fluoropyrimidines and oxaliplatin combination for 6 months. The specific issues faced by patients with stage II colon cancer, including adjuvant chemotherapy in high-risk patients, are discussed. Finally, we describe the distinctive characteristics of patients with colon cancer under 40 years of age and the prospects of adjuvant chemotherapy in patients with colon cancer.

PIK3CA and APC mutations are synergistic in the development of intestinal cancers

Human colorectal cancers are known to possess multiple mutations, though how these mutations interact in tumor development and progression has not been fully investigated. We have previously described the FCPIK3ca* murine colon cancer model, which expresses a constitutively activated phosphoinositide-3 kinase (PI3K) in the intestinal epithelium. The expression of this dominantly active form of PI3K results in hyperplasia and invasive mucinous adenocarcinomas. These cancers form via a non-canonical mechanism of tumor initiation that is mediated through activation of PI3K and not through aberrations in WNT signaling. Since the Adenomatous Polyposis Coli (APC) gene is mutated in the majority of human colon cancers and often occurs simultaneously with PIK3CA mutations, we sought to better understand the interaction between APC and PIK3CA mutations in the mammalian intestine. In this study, we have generated mice in which the expression of a constitutively active PI3K and the loss of APC occur simultaneously in the distal small intestine and colon. Here, we demonstrate that expression of a dominant active PI3K synergizes with loss of APC activity resulting in a dramatic change in tumor multiplicity, size, morphology and invasiveness. Activation of the PI3K pathway is not able to directly activate WNT signaling through the nuclear localization of CTNNB1 (β-catenin) in the absence of aberrant WNT signaling. Alterations at the transcriptional level, including increased CCND1, may be the etiology of synergy between these activated pathways.

Current Lynch syndrome tumor screening practices: a survey of genetic counselors

An electronic survey of the National Society of Genetic Counselors Cancer Special Interest Group was conducted in July 2011 to assess Lynch syndrome tumor screening programs and identify barriers to implementation. Over half of respondents (52.8 %) reported having a routine Lynch syndrome tumor screening protocol for newly diagnosed colon and/or endometrial cancers, and approximately half of these used a universal approach. There was an increase in the number of those screening over time, especially in the past 3 years. Tumor screening methods varied; 34/53 (64.2 %) started with immunohistochemistry, 11/53 (20.8 %) started with microsatellite instability testing and 8/53 (15.1 %) performed both on newly diagnosed colorectal tumors. Just 21.7 % (23/106) of respondents indicated they have a tumor screening program in place for newly diagnosed endometrial cancers. Written consent is rarely obtained (7.1 %) and the method of how results were returned to the patient was variable among respondents. Prevalent barriers to implementation were concern about cost, bringing key players together and convincing medical staff of the necessity. Use of Lynch syndrome tumor screening is in clinical practice, but protocols vary widely. This survey provides a glimpse of current practices and common barriers, and identifies the need for tumor screening algorithms with outcomes data.

Underutilization of Lynch syndrome screening in a multisite study of patients with colorectal cancer

PURPOSE

The aim of this study was to examine Lynch syndrome screening of patients with metastatic colorectal cancer in integrated health-care-delivery organizations.

METHODS

We determined the availability of Lynch syndrome screening criteria and actual Lynch syndrome screening in the medical records of 1,188 patients diagnosed with metastatic colorectal cancer between 2004 and 2009 at seven institutions in the Cancer Research Network.

RESULTS

We found infrequent use of Lynch syndrome screening (41/1,188). Family history was available for 937 of the 1,188 patients (79%). There was sufficient information to assess Lynch syndrome risk using family history-based criteria in 719 of the 937 patients (77%) with family history documentation. In 391 individuals with a family history of a Lynch syndrome-associated cancer, 107 (27%) could not be evaluated due to missing information such as age of cancer onset. Eleven percent of patients who met the Bethesda criteria and 25% of individuals who met the Amsterdam II criteria were screened for Lynch syndrome. Recommended guidelines were adhered to during screening, but no testing method was preferred.

CONCLUSION

The information required for Lynch syndrome screening decisions is routinely collected but seldom used. There is a critical gap between collection of family history and its use to guide Lynch syndrome screening, which may support a case for implementation of universal screening guidelines.

Histopathologic features and microsatellite instability of sporadic colorectal carcinoma: An analysis of 400 cases

AIM: To investigate the clinicopathologic features of sporadic colorectal carcinoma with high level of microsatellite instability (MSI-H), detect deficient expression of DNA mismatch repair protein, predict tumor microsatellite instability (MSI) status, and create a platform for diagnosis and screening of genetic colorectal carcinoma.

METHODS: Clinical data for 400 cases of sporadic colorectal carcinoma were analyzed. All cases underwent histological assessment. The deficiency expression of mismatch repair protein was detected by immunohistochemistry. The MSI status of carcinoma was predicted and then confirmed by PCR.

RESULTS: Male patients and left-side location predominated in the present series. Of 400 cases of sporadic colorectal carcinoma, 18 cases of MSI-H, 98 cases of MSI-L and 284 cases of MSS were detected by immunohistochemistry. Pathological features of MSI-H colorectal carcinoma included villous and papilloma structures, poor or good differentiation, mucinous type, signet-cell carcinoma or any mucinous differentiation, increased tumor-infiltrating lymphocytes (TIL cells), the presence of Crohn-like reaction, and the lack of necrosis. PCR analysis confirmed that there were 7 cases of MSI-H tumors, 1 case of MSI-L, 6 cases of MSS and 4 cases of allele of heterozygosity.

CONCLUSION: Sporadic MSI-H colorectal carcinoma has unique morphology, but shows no correlation with patient age, sex, and tumor size. Morphological assessment with immunohistochemistry can be used as a routine method for screening MSI-H and genetic colorectal carcinoma and guiding individualized treatment.

MUTYH-associated colorectal cancer and adenomatous polyposis

MUTYH-associated polyposis (MAP) was first described in 2002. MUTYH is a component of a base excision repair system that protects the genomic information from oxidative damage. When the MUTYH gene product is impaired by bi-allelic germline mutation, it leads to the mutation of cancer-related genes, such as the APC and/or the KRAS genes, via G to T transversion. MAP is a hereditary colorectal cancer syndrome inherited in an autosomal-recessive fashion. The clinical features of MAP include the presence of 10-100 adenomatous polyps in the colon, and early onset of colorectal cancer. Ethnic and geographical differences in the pattern of the MUTYH gene mutations have been suggested. In Caucasian patients, c.536A>G (Y179C) and c.1187G>A (G396D) mutations are frequently detected. In the Asian population, Y179C and G396D are uncommon, whereas other variants are suggested to be the major causes of MAP. We herein review the literature on MUTYH-associated colorectal cancer and adenomatous polyposis.

Oncogenic mutations and microsatellite instability phenotype predict specific anatomical subsite in colorectal cancer patients

In colorectal cancer (CRC) oncogenic mutations such as KRAS alterations, are considered standard molecular biomarkers that predict the clinical benefit for targeted intervention with epidermal growth factor receptor (EGFR) inhibitors. In addition, these mutations are associated with specific anatomical area in colon tumor development, as BRAF mutations with the microsatellite instability (MSI). In this translational study, we aimed to assess the mutation frequencies of the EGFR (hotspot area and polyadenine deletions A13_del), KRAS, BRAF(V600E), and PIK3CA oncogenes in a series of 280 CRC patients. MSI phenotypes are also considered in this series. All patients' clinicopathological data were assessed for statistical analysis and its associations were validated. We verified multiple associations between oncogenic mutations and determined clinicopathological tumor features (1) EGFR A13_deletions are associated with right colon carcinoma (P<0.005), mucinous histotype (P=0.042), G3 grading (P=0.024), and MSI status (P<0.005); (2) PIK3CA mutations are related mucinous histotype (P=0.021); (3) KRAS(G12) and KRAS(G13) mutations are correlated, respectively, with the left and right colon cancer development (P<0.005), and finally (4) MSI is associated with right colon tumors (P<0.005). Mostly, we verified a higher frequency rate of the KRAS(G13) and EGFR A13_del oncogene mutations in right colon cancer; whereas KRAS(G12) codon mutation occurs more frequently in left colon cancers. In particular, we assessed that right vs left colon cancer are associated with specific molecular characteristics. These evidences, in association with clinicopathological data, can delineate novel approaches for the CRC classification and targeted intervention.

A novel classification of colorectal tumors based on microsatellite instability, the CpG island methylator phenotype and chromosomal instability: implications for prognosis

BACKGROUND

We studied the overlap between the major (epi)genomic events microsatellite instability (MSI), the CpG island methylator phenotype (CIMP) and chromosomal instability (CIN) in colorectal cancer (CRC), and whether specific (epi)genotypes were associated with CRC-related deaths.

PATIENTS AND METHODS

Molecular analyses using tumor DNA were successful in 509 CRC cases identified within the Netherlands Cohort Study in the period 1989-1993. Follow-up for the vital status until May 2005 was 100%.

RESULTS

MSI (12.6%), CIMP-only (5.3%), CIMP + CIN (13.4%), CIN-only (58.2%) and triple-negative tumors (10.6%) differed significantly regarding tumor localization, differentiation grade, initial adjuvant therapy (AT) use and genetic characteristics (P ≤ 0.03). CIMP-only, CIMP + CIN and triple-negative tumors, compared with CIN-only tumors, were significantly associated with a 3.67, 2.44 and 3.78-fold risk of CRC-related deaths after 2-year follow-up (95% confidence intervals, CIs, 1.70-7.91, 1.35-4.41 and 1.97-7.25, respectively), but not after late follow-up. MSI tumors were borderline significantly associated with a 0.40-fold risk of CRC-related deaths after late follow-up (95% CI 0.15-1.03).

CONCLUSION(S)

This is the first study to show that specific (epi)genotypes may hold a differential prognostic value that may vary over time. Although no specific treatment data were available, an explanation for the differential findings over time might be that (epi)genotypes modify therapy response.

Molecular dissection of microsatellite instable colorectal cancer

Colorectal cancer was one of the first solid tumors to be classified on the basis of molecular profiling. Microsatellite instability has allowed researchers to distinguish a specific subtype of colorectal cancer that has a clearly identified molecular origin (mismatch repair deficiency), arises on a hereditary and sporadic basis, is linked to a clear clinicopathologic profile, and has prognostic implications. Inconclusive predictive data along with a paucity of targeted drug development have prevented this molecular classification system from being implemented in the clinical setting. New high-throughput genomic data have validated it, thus stressing the fact that it is ready to be applied clinically.

SIGNIFICANCE

Application of a molecular classification of colorectal cancer in the clinical arena is an unmet promise. Recent results of large-scale genomic analyses have provided confirmation and further insights into the molecular biology of already known colorectal cancer subgroups. The quintessential example is the microsatellite instability subgroup, which has been well characterized during the past 2 decades. Future drug development and clinical research initiatives in colorectal oncology should consider these and other known cancer subgroups and start targeting these selected patient populations.

Prognostic value of microsatellite instability in sporadic locally advanced rectal cancer following neoadjuvant radiotherapy

AIMS

This study was conducted to investigate the clinicopathological significance and prognostic value of microsatellite instability (MSI) in locally advanced rectal cancer (LARC) following neoadjuvant radiotherapy.

METHODS AND RESULTS

A total of 316 consecutive patients with LARC who underwent neoadjuvant radiotherapy and curative surgery were included retrospectively. Microsatellite instability in pretreatment biopsy tissue was assessed using the pentaplex panel of mononucleotides. Twenty-five tumours (7.9%) were assessed as high-frequency MSI (MSI-H) and 291 were low-frequency MSI (MSI-L; n = 42) or microsatellite stable (MSS; n = 249). There were no significant differences in terms of gender, age, tumour location or pretreatment serum carcinoembryonic antigen between the MSI-H and MSI-L + MSS groups. Microsatellite instability was not associated statistically with pathological stage, radiation-induced tumour regression or downstaging. No significant difference was found in disease-free survival (DFS) between the two groups but, within the subgroup of ypN0 stage, patients with MSI-H tumours presented a significantly improved DFS compared with those with MSI-L or MSS tumours (100% versus 79.8%, P < 0.05), whereas no DFS improvement was observed for patients with MSI-H tumours in the ypN + subgroup.

CONCLUSIONS

Microsatellite instability could not predict a histopathological response to neoadjuvant radiotherapy, but was a good prognostic marker for patients without lymph node metastasis after neoadjuvant radiotherapy.

Era of universal testing of microsatellite instability in colorectal cancer

Colorectal cancer (CRC) incidence and mortality are constantly decreasing, but CRC still remains the third most prevalent cancer and the third most common cause of cancer death in both males and females in the United States. Recent rapid declines in CRC incidence rates have largely been attributed to increases in screening that can detect and remove precancerous polyps, and the decrease in death rates for CRC largely reflects improvements in early detection, treatment and the understanding of molecular/genetic basis of CRC. One of the important molecular/genetic findings is the presence of microsatellite instability (MSI) in CRCs. Many studies have shown the importance of MSI testing in diagnosing Lynch syndrome and predicting prognosis and response to chemotherapeutic agents in CRCs. Increased emphasis has been placed on the importance of MSI testing for all newly diagnosed individuals with CRCs. Both immunohistochemical staining (IHC) and polymerase chain reaction (PCR)-based MSI testing show high sensitivity and specificity in detecting MSI. The current clinical guidelines and histopathology features are indicative of, but not reliable in diagnosing Lynch syndrome and CRCs with MSI. Currently, there are evidences that universal testing for MSI starting with either IHC or PCR-based MSI testing is cost effective, sensitive, specific and is getting widely accepted.

Therapeutic implications of DNA mismatch repair in adjuvant colorectal cancer chemotherapy

SUMMARY Microsatellite instability (MSI) is a molecular marker of defective DNA mismatch repair (MMR) and constitutes an important oncogenic molecular pathway in colorectal cancer that is present in approximately 12–15% of all colorectal malignant tumors. Defective MMR status in colorectal cancer occurs as a result of germline mutations in MMR genes (less than one third of cases) or, more commonly, from somatic hypermethylation of the MLH1 promoter (more than two thirds). MMR deficiency accelerates colorectal oncogenesis by accumulation of secondary mutations in specific target genes. Patients with defective MMR tumors have distinct clinicopathologic characteristics and have been associated with a better stage-adjusted prognosis than patients with proficient MMR tumors. MMR deficiency may predict tumor chemoresistance to adjuvant 5-fluorouracil treatment. Preliminary clinical data suggested that adding oxaliplatin to 5-fluorouracil could restore the benefit of adjuvant chemotherapy in MSI patients. Further studies are needed to clarify the differential chemosensitivity of MSI patients depending on the mechanism of MMR deficiency and the adjuvant chemotherapeutic regimen used.

Key genetic considerations in the management of suspected hereditary colorectal cancer

SUMMARY Hereditary bowel cancer syndromes account for up to 5% of colorectal cancer (CRC) incidence. Presentation of CRC under the age of 50 years should alert clinicians to a possible underlying genetic predisposition. This article focuses on Lynch syndrome (hereditary nonpolyposis CRC). Regular bowel screening is effective in reducing the risk of CRC and improving overall survival in Lynch syndrome families. The issues surrounding the clinical diagnostic criteria and the shortcomings of the referral process are described, and it is questioned whether a universal strategy for diagnosis should be employed. This article summarizes the evidence for the benefit of bowel screening and suggests practical steps to help ensure compliance with screening recommendations. Finally, it is discussed how collaboration between geneticists, gastroenterologists and surgeons can inform surgical decision-making for the benefit of the patient.

Relative effectiveness and safety of chemotherapy in elderly and nonelderly patients with stage III colon cancer: a systematic review

BACKGROUND

Chemotherapy effectiveness in clinical practice may differ from the efficacy demonstrated in clinical trials, particularly among populations underrepresented in clinical trials, such as elderly patients with cancer. This review aims to examine the relative effectiveness of chemotherapy for stage III colon cancer in elderly versus nonelderly patients.

METHODS

A systematic literature review was conducted using the Agency for Healthcare Research and Quality approach. Literature searches were performed in Medline and Evidence-Based Medicine Reviews databases. Chemotherapy regimens approved for stage III colon cancer were reviewed. Four effectiveness and 15 safety outcomes were extracted.

RESULTS

From 708 identified articles, 25 articles provided data on the relative effectiveness and safety of chemotherapy among elderly versus nonelderly patients. Four of 14 studies showed lower overall survival treatment effects, whereas one of five and one of four studies indicated more favorable treatment effects for time to progression and overall response rate. Grade 3 or 4 adverse events were higher among elderly patients for cardiac disorder (2/5 studies), leukopenia (1/5), neutropenia (4/16), thrombocytopenia (2/13), febrile neutropenia (1/4), infection (2/10), dehydration (2/6), diarrhea (6/20), and fatigue (6/13). Grade 3 or 4 adverse events were lower for neutropenia (2/16 studies), nausea/vomiting (1/16), and neuropathy (1/9).

CONCLUSION

The majority of the evidence suggests that chemotherapy has similar relative effectiveness and safety for patients >65 years of age versus younger patients with stage III colon cancer. When differences are reported, treatment effects are more often worse among the elderly. This review suggests that without other reasons for withholding treatment, elderly patients should receive chemotherapy as often as nonelderly patients.

Microsatellite instability has a positive prognostic impact on stage II colorectal cancer after complete resection: results from a large, consecutive Norwegian series

Background

Microsatellite instability (MSI) was suggested as a marker for good prognosis in colorectal cancer in 1993 and a systematic review from 2005 and a meta-analysis from 2010 support the initial observation. We here assess the prognostic impact and prevalence of MSI in different stages in a consecutive, population-based series from a single hospital in Oslo, Norway.

Patients and methods

Of 1274 patients, 952 underwent major resection of which 805 were included in analyses of MSI prevalence and 613 with complete resection in analyses of outcome. Formalin-fixed tumor tissue was used for PCR-based MSI analyses.

Results

The overall prevalence of MSI was 14%, highest in females (19%) and in proximal colon cancer (29%). Five-year relapse-free survival (5-year RFS) was 67% and 55% (P = 0.030) in patients with MSI and MSS tumors, respectively, with the hazard ratio (HR) equal to 1.60 (P = 0.045) in multivariate analysis. The improved outcome was confined to stage II patients who had 5-year RFS of 74% and 56% respectively (P = 0.010), HR = 2.02 (P = 0.040).

Examination of 12 or more lymph nodes was significantly associated with proximal tumor location (P < 0.001).

Conclusions

MSI has an independent positive prognostic impact on stage II colorectal cancer patients after complete resection.

Psychological distress in newly diagnosed colorectal cancer patients following microsatellite instability testing for Lynch syndrome on the pathologist's initiative

According to the Dutch Guideline on Hereditary Colorectal Cancer published in 2008, patients with recently diagnosed colorectal cancer (CRC) should undergo microsatellite instability (MSI) testing by a pathologist immediately after tumour resection if they are younger than 50 years, or if a second CRC has been diagnosed before the age of 70 years, owing to the high risk of Lynch syndrome (MIPA). The aim of the present MIPAPS study was to investigate general distress and cancer-specific distress following MSI testing. From March 2007 to September 2009, 400 patients who had been tested for MSI after newly diagnosed CRC were recruited from 30 Dutch hospitals. Levels of general distress (SCL-90) and cancer-specific distress (IES) were assessed immediately after MSI result disclosure (T1) and 6 months later (T2). Response rates were 23/77 (30%) in the MSI-positive patients and 58/323 (18%) in the MSI-negative patients. Levels of general distress and cancer-specific distress were moderate. In the MSI-positive group, 27% of the patients had high general distress at T1 versus 18% at T2 (p = 0.5), whereas in the MSI-negative group, these percentage were 14 and 18% (p = 0.6), respectively. At T1 and T2, cancer-specific distress rates in the MSI-positive group and MSI-negative group were 39 versus 27% (p = 0.3) and 38 versus 36% (p = 1.0), respectively. High levels of general distress were correlated with female gender, low social support and high perceived cancer risk. Moderate levels of distress were observed after MSI testing, similar to those found in other patients diagnosed with CRC. Immediately after result disclosure, high cancer-specific distress was observed in 40% of the MSI-positive patients.

Biomarkers in early-stage colorectal cancer: ready for prime time?

BACKGROUND/AIMS

During the last two decades, hundreds of reports have detailed putative prognostic and predictive biomarkers for colorectal cancer (CRC). However, the majority of these studies have been small and retrospective, reporting results that are highly likely to represent false positives. Consequently, their relevance to clinical practice requires definition.

METHODS

Review of published literature on CRC biomarkers, focusing on early-stage disease.

RESULTS

Although most putative biomarkers have failed to be validated in subsequent studies, level I evidence now indicates that tumour microsatellite instability can be used to identify a cohort of patients with stage IIA disease at low risk of relapse who can be spared adjuvant chemotherapy. Emerging data suggest that gene expression arrays may have a role in selecting patients with stage IIA disease and mismatch repair-proficient tumours for chemotherapy following tumour resection.

CONCLUSION

Despite the profusion of biomarker literature, only mismatch repair status can be recommended as routine in current clinical practice. High-quality, adequately powered studies are essential to accurately define the utility of existing and putative biomarkers, and to support their rational application in the clinic.

A robust genomic signature for the detection of colorectal cancer patients with microsatellite instability phenotype and high mutation frequency

Microsatellite instability (MSI) occurs in 10-20% of colorectal tumours and is associated with good prognosis. Here we describe the development and validation of a genomic signature that identifies colorectal cancer patients with MSI caused by DNA mismatch repair deficiency with high accuracy. Microsatellite status for 276 stage II and III colorectal tumours has been determined. Full-genome expression data was used to identify genes that correlate with MSI status. A subset of these samples (n = 73) had sequencing data for 615 genes available. An MSI gene signature of 64 genes was developed and validated in two independent validation sets: the first consisting of frozen samples from 132 stage II patients; and the second consisting of FFPE samples from the PETACC-3 trial (n = 625). The 64-gene MSI signature identified MSI patients in the first validation set with a sensitivity of 90.3% and an overall accuracy of 84.8%, with an AUC of 0.942 (95% CI, 0.888-0.975). In the second validation, the signature also showed excellent performance, with a sensitivity 94.3% and an overall accuracy of 90.6%, with an AUC of 0.965 (95% CI, 0.943-0.988). Besides correct identification of MSI patients, the gene signature identified a group of MSI-like patients that were MSS by standard assessment but MSI by signature assessment. The MSI-signature could be linked to a deficient MMR phenotype, as both MSI and MSI-like patients showed a high mutation frequency (8.2% and 6.4% of 615 genes assayed, respectively) as compared to patients classified as MSS (1.6% mutation frequency). The MSI signature showed prognostic power in stage II patients (n = 215) with a hazard ratio of 0.252 (p = 0.0145). Patients with an MSI-like phenotype had also an improved survival when compared to MSS patients. The MSI signature was translated to a diagnostic microarray and technically and clinically validated in FFPE and frozen samples.

Thymidylate synthase expression and prognosis in colorectal cancer: a meta-analysis of colorectal cancer survival data

BACKGROUND

Although many studies have investigated the prognostic effect of thymidylate synthase (TS) in colorectal cancer, no consensus has been reached. The aim of this meta-analysis was to obtain a more precise estimate of the prognostic significance of TS expression in localized cancers treated by curative resection and adjuvant chemotherapy.

MATERIALS AND METHOD

Seventeen eligible studies reporting survival in 2,893 patients stratified by TS expression were pooled using a fixed- or random-effects model. The main outcome measure was hazard ratio (HR).

RESULTS

The overall HR for overall survival was 1.01 (95% CI 0.74-1.39, p=0.947), with an I2 of 64.4%. The total HR for disease-free survival was 1.36 (95% CI 0.97-1.89, p=0.072), with an I2 of 75.8%. In the TS protein-tested subgroup, the total HR for disease-free survival was 1.72 (95% CI 1.02-2.89, p=0.042), with an I2 of 81.3%.

CONCLUSION

Our meta-analysis showed that, in the adjuvant setting, TS expression does not predict a poorer disease-free survival or a worse overall survival. Therefore, we believe that it is inappropriate to regard TS expression as a prognostic factor for patients with stage II and stage III colorectal cancer treated by surgery and adjuvant chemotherapy.

Molecular pathways in colorectal cancer

Colorectal cancer (CRC) is the second most common newly diagnosed cancer and accounts for the second highest number of cancer related deaths in Australia, the third worldwide and of increasing importance in Asia. It arises through cumulative effects of inherited genetic predispositions and environmental factors. Genomic instability is an integral part in the transformation of normal colonic or rectal mucosa into carcinoma. Three molecular pathways have been identified: these are the chromosomal instability (CIN), the microsatellite instability (MSI), and the CpG Island Methylator Phenotype (CIMP) pathways. These pathways are not mutually exclusive, with some tumors exhibiting features of multiple pathways. Germline mutations are responsible for hereditary CRC syndromes (accounting for less than 5% of all CRC) while a stepwise accumulation of genetic and epigenetic alterations results in sporadic CRC. This review aims to discuss the genetic basis of hereditary CRC and the different pathways involved in the process of colorectal carcinogenesis.

Promoter CpG island methylation markers in colorectal cancer: the road ahead

Despite increasing knowledge on the biology, detection and treatment of colorectal cancer (CRC), the disease is still a major health problem. Hypermethylation of promoter regions of genes has been studied extensively as a contributor in CRC carcinogenesis. In addition, it is the topic of many studies focusing on biomarkers for the early detection, prediction of prognosis and treatment outcome. Methylation markers may be preferred over current screening and test methods as they are stable and easy to detect. However, almost no methylation marker is currently being used in clinical practice, often due to a lack of sensitivity, specificity, or validation of the results. This review summarizes the current knowledge of hypermethylation biomarkers for CRC detection, progression and treatment outcome.

Microsatellite instability in sarcoma: fact or fiction?

Microsatellite instability (MSI) is a unique molecular abnormality, indicative of a deficient DNA mismatch repair (MMR) system. Described and characterized in the colorectal cancer literature, the MSI-positive phenotype is predictive of disease susceptibility, pathogenesis, and prognosis. The clinical relevance of MSI in colorectal cancer has inspired similar inquisition within the sarcoma literature, although unfortunately, with very heterogeneous results. Evolving detection techniques, ill-defined sarcoma-specific microsatellite loci and small study numbers have hampered succinct conclusions. The literature does suggest that MSI in sarcoma is observed at a frequency similar to that of sporadic colorectal cancers, although there is little evidence to suggest that MSI-positive tumors share distinct biological attributes. Emerging evidence in Ewing sarcoma has demonstrated an intriguing mechanistic role of microsatellite DNA in the activation of key EWS/FLI-target genes. These findings provide an alternative perspective to the biological implications of microsatellite instability in sarcoma and warrant further investigation using sophisticated detection techniques, sensitive microsatellite loci, and appropriately powered study designs.

Study protocol of the SACURA trial: a randomized phase III trial of efficacy and safety of UFT as adjuvant chemotherapy for stage II colon cancer

BACKGROUND

Adjuvant chemotherapy for stage III colon cancer is internationally accepted as standard treatment with established efficacy, but the usefulness of adjuvant chemotherapy for stage II colon cancer remains controversial. The major Western guidelines recommend adjuvant chemotherapy for "high-risk stage II" cancer, but this is not clearly defined and the efficacy has not been confirmed.

METHODS/DESIGN

SACURA trial is a multicenter randomized phase III study which aims to evaluate the superiority of 1-year adjuvant treatment with UFT to observation without any adjuvant treatment after surgery for stage II colon cancer in a large population, and to identify "high-risk factors of recurrence/death" in stage II colon cancer and predictors of efficacy and adverse events of the chemotherapy. Patients aged between 20 and 80 years with curatively resected stage II colon cancer are randomly assigned to a observation group or UFT adjuvant therapy group (UFT at 500-600 mg/day as tegafur in 2 divided doses after meals for 5 days, followed by 2-day rest. This 1-week treatment cycle is repeated for 1 year). The patients are followed up for 5 years until recurrence or death. Treatment delivery and adverse events are entered into a web-based case report form system every 3 months. The target sample size is 2,000 patients. The primary endpoint is disease-free survival, and the secondary endpoints are overall survival, recurrence-free survival, and incidence and severity of adverse events. In an additional translational study, the mRNA expression of 5-FU-related enzymes, microsatellite instability and chromosomal instability, and histopathological factors including tumor budding are assessed to evaluate correlation with recurrences, survivals and adverse events.

DISCUSSION

A total of 2,024 patients were enrolled from October 2006 to July 2010. The results of this study will provide important information that help to improve the therapeutic strategy for stage II colon cancer.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00392899.

Molecular testing in colorectal cancer: diagnosis of Lynch syndrome and personalized cancer medicine

Currently, molecular testing in colorectal cancer (CRC) is aimed at detecting Lynch syndrome and predicting response to anti-epidermal growth factor receptor (EGFR) therapies. However, CRC is a complex disease, with at least 3 molecular pathways of carcinogenesis. The importance of the EGFR signaling pathway in colorectal carcinogenesis is underscored by the availability of anti-EGFR monoclonal antibodies for the treatment of some metastatic CRCs. Potentially, mutations in any of the genes in the EGFR signaling pathway may be associated with prognosis and may predict response to anti-EGFR or other targeted therapies. Although not currently the standard of care, molecular testing of CRCs is expanding to include mutational analysis of the genes in the EGFR pathway, in addition to more widely performed tests for identifying cancers with high microsatellite instability. Multiplex molecular prognostic panels for therapeutic decision making in stage II CRCs also represent expanding use of molecular testing for this common cancer.

Eastern Canadian colorectal cancer consensus conference: application of new modalities of staging and treatment of gastrointestinal cancers

The annual Eastern Canadian Colorectal Cancer Consensus Conference was held in Ottawa, Ontario, October 22-23, 2010. Health care professionals involved in the care of patients with colorectal cancer participated in presentation and discussion sessions for the purpose of developing the recommendations presented here. This consensus statement addresses current issues in the management of colorectal cancer, such as the use of epidermal growth factor inhibitors in metastatic colon cancer, the benefit of calcium and magnesium with oxaliplatin chemotherapy, the role of microsatellites in treatment decisions for stage II colon cancer, the staging and treatment of rectal cancer, and the management of colorectal and metastatic pancreatic cancers.

Biomarker use in colorectal cancer therapy

Biomarkers reflective of the molecular and genetic heterogeneity in colorectal cancers now guide certain aspects of clinical management and offer great potential for enrichment, stratification, and identification of novel therapeutic targets in drug development. Using case-based examples, this article reviews biomarkers that have an established role in the clinical management of colorectal cancer: mismatch repair protein testing and KRAS and BRAF mutational analysis. A selection of biomarkers undergoing validation for future clinical application is presented, and the dynamic and challenging interface between biomarkers in research and clinical practice is discussed.

Systematic immunohistochemistry screening for Lynch syndrome in early age-of-onset colorectal cancer patients undergoing surgical resection

BACKGROUND

Lynch syndrome (LS), defined by a deleterious (pathogenic) germline mutation in a mismatch repair (MMR) gene, is characterized by early age-of-onset colorectal cancer (CRC). Because clinical criteria for LS, such as the Amsterdam II Criteria, may miss cases, reflex tumor tissue testing of all CRC patients for LS has been proposed. Our study describes the impact of routine immunohistochemistry (IHC) analysis of tumor tissue for loss of MMR protein expression in early age-of-onset CRC patients undergoing resection.

STUDY DESIGN

A prospective institutional program was established to perform IHC analysis on all early age-of-onset (≤50 years) CRC patients undergoing resection. Patients with abnormal IHC analysis were referred to the Clinical Genetics Service for further evaluation. The study cohort excluded patients with other polyposis syndromes and inflammatory bowel disease.

RESULTS

IHC was performed on 198 patients from July 2006 to June 2010. The median age was 42.8 years (range 23.1 to 50.6 years). Abnormal IHC was reported in 38 (19.1%) patients, and 22 (57.8%) with abnormal IHC analysis had germline genetic testing. Seventeen (77.2%) had an alteration detected in an MMR gene: 10 were known to be deleterious mutations and 7 were variants of uncertain significance. Overall, LS was detected in 5.1% of patients. Only 2 of the 10 (20%) with a deleterious mutation actually met the Amsterdam II Criteria.

CONCLUSIONS

Reflex IHC testing for LS on early age-of-onset CRC patients undergoing resection is feasible at the institutional level. This strategy identifies a substantial number of LS patients who would have been missed if genetic testing was based on the Amsterdam II Criteria alone.

Review of biomarkers in colorectal cancer

AIM

Advances in molecular technology have resulted in the discovery of many putative biomarkers relevant to colorectal cancer (CRC).

METHOD

Literature searches were performed on PubMed and EMBASE using the words 'colorectal cancer', AND 'biomarkers OR markers'. Biomarkers that are either currently in clinical use or have potential clinical use were identified.

RESULTS

Most potential markers are in the discovery phase waiting to undergo clinical validation. Hypermethylation of the plasma septin-9 gene shows promise as a nonstool-based screening tool. Hypermethylation of the DYPD gene (encodes the enzyme dihydropyrimidine dehydrogenase) and variation of the uridine diphosphate-glucuronosyltransferase 1A (UGT1A1) gene have predictive value for side effects and the efficacy of 5-fluoruracil and irinotecan, respectively. Mismatch repair protein immunohistochemistry is able to predict response to 5-fluorouracil, and the KRAS (Kirsten rat sarcoma viral oncogene) and B-RAF (v-RAF murine sarcoma viral oncogene homolog B1) somatic gene mutation status can predict the response to anti-epidermal growth factor receptor therapy.

CONCLUSION

Recent advances indicate that the widespread use of biomarkers may herald the next major advance in the diagnosis and management of CRC.

Clinical effects of adjuvant active specific immunotherapy differ between patients with microsatellite-stable and microsatellite-instable colon cancer

PURPOSE

Active specific immunotherapy (ASI) consisting of an autologous tumor cell vaccine given as adjuvant treatment has been shown to improve recurrence-free survival of patients with colon cancer. The aim of the current retrospective study was to investigate whether the beneficial effects of ASI given as adjuvant treatment correlated with microsatellite instability (MSI), which is considered an important biologic determinant of colon cancer.

EXPERIMENTAL DESIGN

Microsatellite status was assessed on archival tumor material from patients with stage II and III colon cancer. Microsatellite status was next associated with clinical outcome in control and ASI treatment groups using Kaplan-Meier analysis.

RESULTS

We identified 162 (83%) microsatellite-stable tumors (MSS) and 34 (17%) MSI tumors. Patients with MSI tumors did well in recurrence-free interval (RFI) as well as disease-specific survival (DSS) irrespective of treatment arm and tumor stage. Patients with MSI tumors had significantly fewer recurrences and prolonged DSS than those with MSS tumors. Patients with MSS Dukes B tumors who received ASI treatment showed a significantly improved recurrence-free survival compared with controls. ASI treatment did not improve recurrence-free interval or DSS for patients with MSS Dukes C tumors.

CONCLUSION

This retrospective study indicated that patients with MSI tumors did well, irrespective of treatment arm and tumor stage. The data also indicate that the clinical benefit, measured as recurrence-free survival, from adjuvant ASI treatment of patients with colon cancer was restricted to patients with MSS Dukes B tumors.

Mismatch repair status in sporadic colorectal cancer: immunohistochemistry and microsatellite instability analyses

BACKGROUND AND AIM

The aim of the present study was to evaluate associations between mismatch repair (MMR) status and clinicopathological characteristics and prognosis using immunohistochemistry (IHC) and microsatellite instability (MSI) analyses in a prospective cohort of a large number of accumulated samples.

METHODS

Tumor tissue samples obtained during curative surgery (n = 2028) were analyzed using both MLH1/MSH2 IHC and MSI assays. Clinicopathological parameters and survival outcomes were compared according to IHC and MSI results. The median follow-up period was 43 months (range: 1-85 months).

RESULTS

IHC identified 207 tumor samples (10.2%) with a loss of either MLH1 or MSH2 expression. The MSI analysis identified 203 tumor samples (10%) with high-frequency MSI (MSI-H). Patients with MMR defects were younger, and had tumors characterized by right-colon predilection; large-size, infrequent lymph node metastasis; poorly-differentiated or mucinous histology, and synchronous adenomas (P < 0.001-0.008). Patients with MSI-H status had higher 4-year disease-free survival rates than patients with microsatellite stable status (90.8% vs 80.6%, P = 0.001). A multivariate analysis showed that MSI-H status was a good prognostic factor for recurrence (hazard ratio: 0.48, 95% confidence interval: 0.30-0.83, P = 0.007).

CONCLUSIONS

Patients with MMR defects had distinct clinicopathological characteristics, including a lower risk of recurrence. IHC and MSI analyses provided complementary information regarding specific clinicopathological parameters and prognosis.

[Is there alternative to FOLFOX adjuvant chemotherapy for stage III colorectal cancer patients?]

Being the second cancer for men and the third cancer for women in France, colorectal cancer represents a serious public health issue. Its incidence has increased these last years and despite new therapeutics being developed, it still has a bad prognostic. Thanks in part to Hemoccult national mass screening program, its diagnosis is made possible at an earlier stage, which makes a surgical curative resection and the carrying out of adjuvant chemotherapy possible. For stage III colic cancer that has been surgically removed, adjuvant chemotherapy by FOLFOX 4 has to be offered. Nevertheless, because of its toxicities, the patient's high age, important comorbidities or post-surgical complications, this chemotherapy occasionally cannot be done. What are the colorectal cancer prognostic factors which would guide the chemotherapy? TNM classification, number of examined lymph nodes, MSI status, and presence or not of a perforation or a perinervous, lymphatic or venous invasion is recognized prognostic factors. Also, what are the alternatives of FOLFOX 4 regimen as colorectal cancer adjuvant treatment?

Implementing screening for Lynch syndrome among patients with newly diagnosed colorectal cancer: summary of a public health/clinical collaborative meeting

Lynch syndrome is the most common cause of inherited colorectal cancer, accounting for approximately 3% of all colorectal cancer cases in the United States. In 2009, an evidence-based review process conducted by the independent Evaluation of Genomic Applications in Practice and Prevention Working Group resulted in a recommendation to offer genetic testing for Lynch syndrome to all individuals with newly diagnosed colorectal cancer, with the intent of reducing morbidity and mortality in family members. To explore issues surrounding implementation of this recommendation, the Centers for Disease Control and Prevention convened a multidisciplinary working group meeting in September 2010. This article reviews background information regarding screening for Lynch syndrome and summarizes existing clinical paradigms, potential implementation strategies, and conclusions which emerged from the meeting. It was recognized that widespread implementation will present substantial challenges, and additional data from pilot studies will be needed. However, evidence of feasibility and population health benefits and the advantages of considering a public health approach were acknowledged. Lynch syndrome can potentially serve as a model to facilitate the development and implementation of population-level programs for evidence-based genomic medicine applications involving follow-up testing of at-risk relatives. Such endeavors will require multilevel and multidisciplinary approaches building on collaborative public health and clinical partnerships.

Drug therapy for hereditary cancers

Tumors arising in patients with hereditary cancer syndromes may have distinct drug sensitivity as compared to their sporadic counterparts. Breast and ovarian neoplasms from BRCA1 or BRCA2 mutation carriers are characterized by deficient homologous recombination (HR) of DNA, that makes them particularly sensitive to platinum compounds or inhibitors of poly (ADP-ribose) polymerase (PARP). Outstandingly durable complete responses to high dose chemotherapy have been observed in several cases of BRCA-related metastatic breast cancer (BC). Multiple lines of evidence indicate that women with BRCA1-related BC may derive less benefit from taxane-based treatment than other categories of BC patients. There is virtually no reports directly assessing drug response in hereditary colorectal cancer (CRC) patients; studies involving non-selected (i.e., both sporadic and hereditary) CRC with high-level microsatellite instability (MSI-H) suggest therapeutic advantage of irinotecan. Celecoxib has been approved for the treatment of familial adenomatous polyposis (FAP). Hereditary medullary thyroid cancers (MTC) have been shown to be highly responsive to a multitargeted tyrosine kinase inhibitor vandetanib, which exerts specific activity towards mutated RET receptor. Given the rapidly improving accessibility of DNA analysis, it is foreseen that the potential predictive value of cancer-associated germ-line mutations will be increasingly considered in the future studies.

Prognostic and predictive impact of DNA mismatch repair in the management of colorectal cancer

Colorectal cancers develop via two major pathways that include chromosomal instability and microsatellite instability. Microsatellite instability occurs due to deficient DNA mismatch repair (MMR), which can be caused by epigenetic silencing of the MLH1 MMR gene in sporadic colorectal cancers or germline mutations in MMR genes that result in Lynch syndrome. While the molecular origin of deficient MMR differs, sporadic and Lynch syndrome tumors share similar pathological features and have a more favorable stage-adjusted prognosis compared with MMR-proficient cases. While controversy remains, there is evidence to suggest that deficient MMR may predict a lack of benefit from 5-fluorouracil-based adjuvant chemotherapy. The focus of this article is on the MMR phenotype and its prognostic and predictive implications for the management of patients with colorectal cancer.

Genetic testing for lynch syndrome in individuals newly diagnosed with colorectal cancer to reduce morbidity and mortality from colorectal cancer in their relatives

Individuals with Lynch syndrome, sometimes referred to as hereditary non-polyposis colorectal cancer (HNPCC), have an increased risk of developing colorectal cancer (CRC) as well as other cancers. The increased risk is due to inherited mutations in mismatch repair (MMR) genes, which reduce the ability of cells to repair DNA damage. Screening for Lynch syndrome in individuals newly diagnosed with colorectal cancer has been proposed as part of a strategy that combines tests and interventions to reduce the risk of colorectal cancer in the relatives of the colorectal cancer patients with Lynch Syndrome.

Microsatellite instability in the management of colorectal cancer

Microsatellite instability (MSI) is a form of genetic instability caused by alterations in the DNA mismatch repair system. Approximately 15% of colorectal cancers display MSI due to a germline mutation in one of the mismatch repair genes (MLH1, MSH2, MSH6 and PMS2) or to epigenetic silencing of MLH1. Colorectal cancers with MSI have distinctive features, including a tendency to arise in the proximal colon, poor differentiation, lymphocytic infiltration and mucinous or signet-ring histology. Patients with MSI tumors appear to have a better prognosis than those with microsatellite stable tumors, but curiously the responses to 5-fluorouracil-based chemotherapy regimens are poorer with MSI tumors. Preliminary data suggest possible advantages of irinotecan-based regimens, but these findings need validation in well-designed clinical trials.

Genetic-based biomarkers and next-generation sequencing: the future of personalized care in colorectal cancer

The past 5 years have witnessed extraordinary advances in the field of DNA sequencing technology. What once took years to accomplish with Sanger sequencing can now be accomplished in a matter of days with next-generation sequencing (NGS) technology. This has allowed researchers to sequence individual genomes and match combinations of mutations with specific diseases. As cancer is inherently a disease of the genome, it is not surprising to see NGS technology already being applied to cancer research with promises of greater understanding of carcinogenesis. While the task of deciphering the cancer genomic code remains ongoing, we are already beginning to see the application of genetic-based testing in the area of colorectal cancer. In this article we will provide an overview of current colorectal cancer genetic-based biomarkers, namely mutations and other genetic alterations in cancer genome DNA, discuss recent advances in NGS technology and speculate on future directions for the application of NGS technology to colorectal cancer diagnosis and treatment.

Microsatellite instability in colorectal cancer: from molecular oncogenic mechanisms to clinical implications

BACKGROUND

Microsatellite instability (MSI) constitutes an important oncogenic molecular pathway in colorectal cancer (CRC), representing approximately 15% of all colorectal malignant tumours. In roughly one third of the cases, the underlying DNA mismatch repair (MMR) defect is inherited through the transmission of a mutation in one of the genes involved in MMR, predominantly MSH2 and MLH1, or less frequently, MSH6 or PMS2. In the overwhelming number of sporadic cases, MSI results from epigenetic MLH1 silencing through hypermethylation of its promoter. MMR deficiency promotes colorectal oncogenesis through the accumulation of numerous mutations in crucial target genes harbouring mononucleotide repeats, notably in those involved in the control of cell proliferation and differentiation, as well as DNA damage signalling and repair.

DESIGN

In this review, we describe the molecular aspects of the MMR system and the biological consequences of its defect on the oncogenic process, and we discuss the various experimental systems used to evaluate the efficacy of cytotoxic drugs on MSI colorectal cells lines. There is increasing evidence showing that MSI CRCs differ from all CRCs in terms of prognosis and response to the treatment. We report the clinical studies that have evaluated the prognostic and predictive value of MSI status on clinical outcome in patients treated with various chemotherapy regimens used in the adjuvant setting or for advanced CRCs.

CONCLUSION

In view of this, the opportunity of a systematic MSI phenotyping in the clinical management of patients with CRC is further discussed.

Biomarkers in advanced colorectal cancer: challenges in translating clinical research into practice

The growing number of therapeutic agents and known molecular targets in oncology makes the study and clinical use of biomarkers imperative for improving response and survival, reducing toxicity and ensuring economic sustainability. Colorectal cancer, among others, is at the forefront of development of predictive and prognostic biomarkers; however, the difficulty lies in translating potential biomarkers garnered from retrospective analyses in small numbers of patients to generalizable and affordable biomarkers used worldwide. This review outlines the progress made in prognostic and predictive biomarkers in advanced colorectal cancer (ACRC) from the early use of carcinoembryonic antigen (CEA) to the KRAS mutation and beyond. Future challenges are to incorporate standardized and validated methods preferentially during early phases of drug development linked with sophisticated biostatistical support. New trial designs focusing on biomarkers will be essential not only for better understanding of mechanisms of action, but also to make confident 'go or no-go' decisions.

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.

KRAS signaling pathway alterations in microsatellite unstable gastrointestinal cancers

Microsatellite instability (MSI) occurs in about 15% of gastrointestinal cancers and it is associated with specific clinic, pathologic, and molecular features of the tumors. MSI-high (MSI-H) carcinomas also follow specific tumor development pathways. This review is focused on the molecular profile of alterations in members of the KRAS signaling pathway (EGFR, KRAS, BRAF, PIK3CA, RASSF1A, and MLK3 genes) in MSI gastrointestinal carcinomas. Alterations in these genes characterize more than half of gastrointestinal cancers and frequently occur simultaneously in the same tumor, pinpointing the KRAS signaling pathway as one of the most frequently altered pathways in this subset of cancers. Nowadays, many and novel inhibitors targeting molecules of this signaling pathway are being described; therefore, it is worthwhile to test their efficacy in MSI gastrointestinal cancers in order to develop new and more directed targeted therapies for patients affected by this disease.

DNA repair pathways and their implication in cancer treatment

Many cytotoxic agents used in cancer treatment exert their effects through their ability to directly or indirectly damage DNA and thus resulting in cell death. Major types of DNA damage induced by anticancer treatment include strand breaks (double or single strand), crosslinks (inter-strand, intra-strand, DNA-protein crosslinks), and interference with nucleotide metabolism and DNA synthesis. On the other hand, cancer cells activate various DNA repair pathways and repair DNA damages induced by cytotoxic drugs. The purpose of the current review is to present the major types of DNA damage induced by cytotoxic agents, DNA repair pathways, and their role as predictive agents, as well as evaluate the future perspectives of the novel DNA repair pathways inhibitors in cancer therapeutics.

Nonsense mediated decay resistant mutations are a source of expressed mutant proteins in colon cancer cell lines with microsatellite instability

Background

Frameshift mutations in microsatellite instability high (MSI-High) colorectal cancers are a potential source of targetable neo-antigens. Many nonsense transcripts are subject to rapid degradation due to nonsense-mediated decay (NMD), but nonsense transcripts with a cMS in the last exon or near the last exon-exon junction have intrinsic resistance to nonsense-mediated decay (NMD). NMD-resistant transcripts are therefore a likely source of expressed mutant proteins in MSI-High tumours.

Methods

Using antibodies to the conserved N-termini of predicted mutant proteins, we analysed MSI-High colorectal cancer cell lines for examples of naturally expressed mutant proteins arising from frameshift mutations in coding microsatellites (cMS) by immunoprecipitation and Western Blot experiments. Detected mutant protein bands from NMD-resistant transcripts were further validated by gene-specific short-interfering RNA (siRNA) knockdown. A genome-wide search was performed to identify cMS-containing genes likely to generate NMD-resistant transcripts that could encode for antigenic expressed mutant proteins in MSI-High colon cancers. These genes were screened for cMS mutations in the MSI-High colon cancer cell lines.

Results

Mutant protein bands of expected molecular weight were detected in mutated MSI-High cell lines for NMD-resistant transcripts (CREBBP, EP300, TTK), but not NMD-sensitive transcripts (BAX, CASP5, MSH3). Expression of the mutant CREBBP and EP300 proteins was confirmed by siRNA knockdown. Five cMS-bearing genes identified from the genome-wide search and without existing mutation data (SFRS12IP1, MED8, ASXL1, FBXL3 and RGS12) were found to be mutated in at least 5 of 11 (45%) of the MSI-High cell lines tested.

Conclusion

NMD-resistant transcripts can give rise to expressed mutant proteins in MSI-High colon cancer cells. If commonly expressed in primary MSI-High colon cancers, MSI-derived mutant proteins could be useful as cancer specific immunological targets in a vaccine targeting MSI-High colonic tumours.

Referral patterns and adjuvant chemotherapy use in patients with stage II colon cancer

BACKGROUND

Little is known about the actual rate of use of adjuvant chemotherapy in stage II colon cancer and about referral patterns that give patients access to this treatment.

PATIENTS AND METHODS

We searched the tumor registry at Baylor University Medical Center at Dallas to identify patients with stage II colon cancer who underwent resection between 1995 and 2003. The rates of referral to medical oncology and adjuvant chemotherapy use were calculated and potential predictive variables were analyzed using univariate and multivariate techniques.

RESULTS

We identified 287 patients with stage II colon cancer. A total of 160 patients (56%) were referred to a medical oncologist. Eighty patients (28%) received adjuvant chemotherapy. Age < 50 years, private insurance status, lower comorbidity score, higher T stage, and poor tumor differentiation were significant predictors of adjuvant chemotherapy use (P <or= .05).

CONCLUSION

Variability and controversy exist over the use of adjuvant chemotherapy in patients with stage II colon cancer. Our study suggests many patients are not referred to a medical oncologist and may not be fully informed of all treatment options. Referral patterns become more important as a better understanding of recurrence risk is achieved and patient selection for adjuvant chemotherapy is optimized.

Microsatellite instability in colorectal cancer

Approximately 20 percent of right-sided colon cancers and 5 percent of left-sided colon and rectal cancers have a deficient DNA mismatch repair system. This results in the widespread accumulation of mutations to nucleotide repeats, some of which occur within the coding regions of cancer-related genes such as TGFβRII and BAX. A standardized definition for microsatellite instability (MSI) based on the presence of deletions to mononucleotide repeats is gaining widespread acceptance in both research and the clinic. Colorectal cancer (CRC) with MSI are characterized histologically by an abundance of tumor-infiltrating lymphocytes, poor differentiation and a signet ring or mucinous phenotype. In younger patients these tumors usually develop along the chromosomal instability pathway, in which case the mismatch repair genes are inactivated by germline mutation, somatic mutation and loss of heterozygosity. In older patients MSI CRC usually develops against a background of widespread hypermethylation that includes methylation-induced silencing of the mismatch repair gene MLH1. The overall biological and clinical phenotype of MSI CRC that arise in these two pathways is likely to be different and may account for some of the discordant results reported in the literature relating to the clinical properties of these tumors. The available evidence indicates that MSI is unlikely to be a clinically useful marker for the prognostic stratification of early-stage CRC. The predictive value of MSI for response to 5-fluorouracil-based chemotherapy remains controversial, while for other agents the predictive value is difficult to assess because they are used in combination regimens. The MSI phenotype is being actively investigated for novel therapeutic approaches based on the principle of synthetic lethality. Finally, the MSI status of CRC is an extremely useful marker for population-based screening programs that aim to identify individuals and families with the hereditary cancer condition known as Lynch syndrome.