Prognostic and predictive roles of high-degree microsatellite instability in colon cancer: a National Cancer Institute-National Surgical Adjuvant Breast and Bowel Project Collaborative Study

The role of molecular markers in predicting response to therapy in patients with colorectal cancer

Advances in systemic therapy for colorectal cancer have dramatically improved prognosis. While disease stage has traditionally been the main determinant of disease course, several molecular characteristics of tumor specimens have recently been shown to have prognostic significance. Although to date no molecular characteristics have emerged as consistent predictors of response to therapy, retrospective studies have investigated the role of a variety of biomarkers, including microsatellite instability, loss of heterozygosity of 18q, type II transforming growth factor beta receptor, thymidylate synthase, epidermal growth factor receptor, and Kirsten-ras (KRAS). This paper reviews the current literature, ongoing prospective studies evaluating the role of these markers, and novel techniques such as gene profiling, which may help to uncover the more complex molecular interactions that will predict response to chemotherapy in patients with colorectal cancer.

Cell lineage analysis of a mouse tumor

Revealing the lineage relations among cancer cells can shed light on tumor growth patterns and metastasis formation, yet cell lineages have been difficult to come by in the absence of a suitable method. We previously developed a method for reconstructing cell lineage trees from genomic variability caused by somatic mutations. Here, we apply the method to cancer and reconstruct, for the first time, a lineage tree of neoplastic and adjacent normal cells obtained by laser microdissection from tissue sections of a mouse lymphoma. Analysis of the reconstructed tree reveals that the tumor initiated from a single founder cell, approximately 5 months before diagnosis, that the tumor grew in a physically coherent manner, and that the average number of cell divisions accumulated in cancerous cells was almost twice than in adjacent normal lung epithelial cells but slightly less than the expected figure for normal B lymphocytes. The cells were also genotyped at the TP53 locus, and neoplastic cells were found to share a common mutation, which was most likely present in a heterozygous state. Our work shows that the ability to obtain data regarding the physical appearance, precise anatomic position, genotypic profile, and lineage position of single cells may be useful for investigating cancer development, progression, and interaction with the microenvironment.

Differences and evolution of the methods for the assessment of microsatellite instability

Microsatellite instability (MSI) originates from the systematic accumulation of uncorrected deletion/insertion in repetitive DNA tracts in cancer cells with a deficient mismatch repair system. Among colorectal cancers, the MSI signature identifies hereditary cases arising in patients with germline mutations in hMLH1, hMSH2, PMS2 and a fraction of those with hMSH6 mutations, as well as sporadic cancers with epigenetic hMLH1 promoter hypermethylation. Considering the specific pathogenesis, pathological features, natural history and response to 5-fluoro-uracil-based chemotherapy of the MSI cancers, confusion about the genetic markers for MSI recognition seems surprising. In this clinically relevant field, an agreement has not been reached concerning the use of di- or mononucleotide markers for MSI assessment. The Revised Bethesda Guidelines still recommend a panel of markers consisting of mono- and dinucleotides, despite being questioned whether it is congruous to continue to use dinucleotide markers for MSI identification. In any event, no single marker is accurate enough for MSI testing, and an awareness of their pros and cons is required for proper interpretation of results. In recent years, several papers have reported different prevalence of MSI in unrelated series, largely depending on the detection and classification method, suggesting that MSI test interpretation also requires the understanding of the phenomenon rather than simply the crude satisfaction of panel recommendations. Inaccuracies can otherwise lead to under- or overdiagnosis and inaccurate disease classification, which always have a negative impact on the clinical practice of medicine.

P53 mutations in colorectal cancer from northern Iran: Relationships with site of tumor origin, microsatellite instability and K-ras mutations

CRC-associated P53 mutations have not been studied extensively in non-Western countries at relatively low CRC risk. We examined, for the first time, 196 paraffin-embedded CRC cases from Northern Iran for mutations in P53 exons 5-8 using PCR-direct sequencing. P53 status and mutation site/type were correlated with nuclear protein accumulation, clinicopathologic variables and data on K-ras mutations and high-level microsatellite instability (MSI-H). We detected 96 P53 mutations in 87 (44.4%) cases and protein accumulation in 84 cases (42.8%). P53 mutations correlated directly with stage and inversely with MSI-H. Distal CRCs were more frequently mutated at major CpG hotspot codons [248 (8/66, 12.1%), 175 (7/66, 10.6%), and 245 (7/66, 10.6%)], while in proximal tumors codon 213, emerged as most frequently mutated (5/28, 17.9% vs. 3/66, 4.5%, P = 0.048). Transitions at CpGs, the most common mutation type, were more frequent in non-mucinous (25% vs. 10.4% in mucinous, P = 0.032), and distal CRC (27% vs. 12.5% in proximal, P = 0.02), and correlated with K-ras transversions. Transitions at non-CpGs, second most common P53 mutation, were more frequent in proximal tumors (15.6% vs. 4.7% in distal, P = 0.01), and correlated with K-ras transitions and MSI-H. Overall frequency and types of mutations and correlations with P53 accumulation, stage and MSI-H were as reported for non-Iranian patients. However P53 mutation site/type and correlations between P53 and K-ras mutation types differed between proximal and distal CRC. The codon 213 P53 mutation that recurred in proximal CRC was previously reported as frequent in esophageal cancer from Northern Iran.

Individual tumorigenesis pathways of sporadic colorectal adenocarcinomas are associated with the biological behavior of tumors

Clinicopathologic features of sporadic colorectal adenocarcinomas were compared using integrated data from 224 [corrected] patients subjected to curative resection. Individual steps in the tumorigenesis pathway, that is, adenomatosis polyposis coli (APC), Wnt-activated, base excision repair mutations, mismatch repair defects, RAF-mediated, transforming growth factor (TGF)-beta-suppressed, bone morphogenic protein (BMP)-suppressed, and p53 alterations, were examined in terms of genetic and epigenetic changes, as well as protein expression. Genetic and molecular alterations of right colon cancers were distinct from those of left colon and rectal cancers. Rectal cancers showed the attenuated phenotype of left colon cancers. Tumors most frequently displayed either TGF-beta- or BMP-suppressed alterations (81.2%), followed by RAF-mediated alterations (78.6%), and mismatch repair defects (38.4%), constituting a total of 24 integrated pathways. Tumors lacking APC mutations or carrying the RAF alteration (V600E) were frequently associated with lymphovascular invasion and lymph node metastasis (P < 0.05). Poorly differentiated or mucinous adenocarcinomas were generally associated with high level microsatellite instability, Axin2 suppression, TGF-beta1 or BMPR1A suppression, loss of heterozygosity of D18S46 or D18S474, and absence of base excision repair mutations (P < 0.0001-0.05). Early tumor recurrence was significantly correlated with lack of APC mutations (P = 0.036). Moreover, tumors that concurrently displayed APC/Wnt-activated, TGF-beta/BMP-suppressed, and p53 alterations were significantly predisposed to early recurrence (P = 0.026). Our data clearly indicate that particular steps or pathways of colorectal tumorigenesis are closely associated with characteristic clinicopathologic features that, in turn, determine biological behavior, such as tumor growth, invasion, and recurrence.

Progress in the development of prognostic and predictive markers for gastrointestinal malignancies

Gastrointestinal cancers remain a significant cause of morbidity and mortality. While increasing therapeutic options have improved outcomes for many patients, they have also complicated treatment decision-making. Unfortunately, most patients with advanced gastrointestinal malignancies die from their disease. Prognostic and predictive markers could improve treatment significantly by identifying patients who may or may not require a given therapy, and determining those most likely to benefit from a therapy. Candidates for such markers include blood antigens and circulating tumor cells, tumor enzyme and gene expression, and pharmacodynamic endpoints. In this review, we summarize reported and ongoing research to define and validate prognostic and predictive markers in gastrointestinal malignancies, with an emphasis on colorectal cancer and brief overview of pancreatic and neuroendocrine tumors.

Targeted therapy of cancer: new roles for pathologists in colorectal cancer

Personalized/individualized/tailored therapy for each patient is an important goal for improving the outcome of patients with colorectal adenocarcinoma and includes the intention to maximize efficacy and minimize toxicity of chemotherapeutic agents. Numerous barriers must be overcome to reach this goal because outcome is affected by an unholy trinity of tumor characteristics that include somatic alterations at the DNA, RNA, and protein level; patient characteristics that include germline genetic differences such as polymorphisms in enzymes affecting the metabolism of chemotherapeutic agents; and environmental exposures and factors that include diet and physical activity. At present, evaluation of epidermal growth factor receptor (EGFR) expression by immunohistochemistry in colorectal adenocarcinoma is generally required for treatment with one of the monoclonal antibody therapies directed against that target, despite the absence of evidence for predictive value of the assay, whereas EGFR fluorescent in situ hybridization (FISH) may be predictive. In addition, the Food and Drug Administration of the United States now requires a 'black box' warning on the packaging of irinotecan for evaluation of germline polymorphism in UGT1A1, the gene mutated in Gilbert's syndrome, for potential reduction of drug dosage in patients with the UGT1A1*28 polymorphism. Numerous other potential markers have been identified but have not yet reached levels of evidence that support their routine usage. For example, KRAS gene mutation appears to preclude improved survival after therapy with monoclonal antibody therapy directed at EGFR, and extensive DNA methylation is associated with lack of efficacy of 5-fluorouracil (5-FU)-based chemotherapy. Additional markers will come into routine usage as reports of research studies continue to appear in the literature. Clinical trials driven by molecular targets and agents directed against them, and understanding of the conflicting data on utility of markers reported in the literature, are needed to advance the field.

Molecular prognostic markers in locally advanced colon cancer

For patients who undergo successful surgery for colon cancer, additional chemotherapy is recommended in high-risk stage II and stage III disease. Colorectal cancer prognosis is stage and grade dependent, and many tumors with similar histopathologic features show significantly different clinical outcomes. Therefore, tumor recurrence after curative resection continues to be a significant problem in the management of colon cancer, and approximately 50% of patients will develop recurrent disease. There are a few clinical and potential molecular markers that can predict clinical outcome in locally advanced colon cancer. Accordingly, the development of molecular markers of prognosis is critical in making a tailored adjuvant treatment with molecular stratification possible. Many new biomarkers have been investigated; however, none of them have yet been validated in large prospective clinical trials. To date, the two most promising and most studied mechanisms of genomic instability are chromosomal instability with deletion of chromosome 18q and 17p and microsatellite instability (MSI). Eastern Cooperative Oncology Group 5202 is a prospective clinical trial which is randomizing patients with stage II disease based on their MSI and 18q status to observation versus adjuvant chemotherapy with the intention of prospectively determining their prognostic value as molecular markers. This review will discuss the most promising molecular prognostic markers and provide an update on the most recent developments.

Carcinogenesis and microsatellite instability: the interrelationship between genetics and epigenetics

DNA mismatch repair (MMR) deficiency results in a strong mutator phenotype and high-frequency microsatellite instability (MSI-H), which are the hallmarks of tumors arising within Lynch syndrome. MSI-H is characterized by length alterations within simple repeated sequences, microsatellites. Lynch syndrome is primarily due to germline mutations in one of the DNA MMR genes; mainly hMLH1 or hMSH2 and less frequently hMSH6 and rarely hPMS2. Germline hemiallelic methylation of MLH1, termed epimutation, has been reported to be a new cause of Lynch syndrome. MSI-H is also observed in approximately 15% of colorectal, gastric and endometrial cancers and in lower frequencies in a minority of other tumors, where it is associated with the hypermethylation of the promoter region of hMLH1. MSI-H underlies a distinctive tumorigenic pathway because cancers with MSI-H exhibit many differences in genotype and phenotype relative to cancers without MSI-H, irrespective of their hereditary or sporadic origins. Genetic, epigenetic and transcriptomic differences exist between cancers with and those without the MSI-H. The BRAF V600E mutation is associated with sporadic MSI-H colorectal cancers (CRCs) harboring hMLH1 methylation but not Lynch syndrome-related CRCs. The differences in genotype and phenotype between cancers with and those without MSI-H are likely to be causally linked to their differences in biological and clinical features. Therefore, the diagnosis of MSI-H in cancers is thus considered to be of increasing relevance, because MSI-H is a useful screening marker for identifying patients with Lynch syndrome, a better prognostic factor and could affect the efficacy of chemotherapy. This review addresses recent advances in the field of microsatellite instability research.

Adjuvant therapy of colon cancer: current status and future directions

Adjuvant treatment of colon cancer is a relatively new concept, having been first validated less than 20 years ago. Fluoropyrimidines including 5-fluorouracil (5-FU), introduced in clinical trials in the 1950s, are an integral component of the treatment of colon cancer in the adjuvant setting. Whereas both irinotecan and oxaliplatin have demonstrated clinical activity in metastatic colorectal cancer, only oxaliplatin has demonstrated efficacy in the adjuvant setting when added to 5-FU-based therapy. Irinotecan, despite showing a survival advantage in the second-line metastatic cancer setting and a survival advantage when added to first-line metastatic cancer treatment, has failed to show a survival or disease-free survival benefit in the adjuvant setting. In contradistinction, the addition of oxaliplatin to 5-FU plus leucovorin has improved disease-free survival in 2 large randomized adjuvant trials. Oxaliplatin/5-FU/leucovorin should therefore be regarded as a reference standard for adjuvant therapy. This comprehensive review of adjuvant therapy for colon cancer will cover the role of fluoropyrimidines and oxaliplatin, the controversies of adjuvant therapy for patients with stage II cancer, and the ongoing clinical trials that will define the future role, or lack thereof, of newer agents in adjuvant therapy.

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.

Adjuvant therapy for colon cancer

In patients with colon cancer who undergo resection for potential cure, 40% to 60% have advanced locoregional disease and are classified as either stage II or stage III. The role of adjuvant therapy in stage III colon cancer is well defined. The results from the MOSAIC trial (Multicenter International Study of Oxaliplatin/5-Fluorouracil/Leucovorin in the Adjuvant Treatment of Colon Cancer) and the National Surgical Adjuvant Breast and Bowel Project C-07 trial confirm a definite disease-free survival (DFS) benefit with the addition of oxaliplatin to either infusional or bolus 5-fluorouracil/leucovorin (5-FU/LV). The Xeloda in Adjuvant Colon Cancer Therapy (X-ACT) trial showed capecitabine to be of equivalent clinical benefit to bolus 5-FU/LV. However, adjuvant trials with irinotecan, including Cancer and Leukemia Group B (CALGB 89803), the Pan-European Trial in Adjuvant Colorectal Cancer 3 (PETACC-3), and the French ACCORD trial, have not shown a significant DFS advantage. In contrast, in patients with stage II disease, a small survival benefit of 1% to 5% exists with chemotherapy. Perhaps the analysis of molecular markers in combination with high-risk histopathologic features will help increase patient specificity and identify subsets of patients with stage II colon cancer who will derive a survival benefit with adjuvant therapy. The current Intergroup study stratifying stage II patients based on presence of microsatellite instability and loss of heterozygosity 18q allele will help us better understand the risk versus benefit observed.

The features of host immune response with respect to microsatellite status of colorectal cancer

Background: The genetic alterations in colorectal cancer (CRC) progression are determined by two separate pathways, chromosomal and microsatellite instability (MSI). The CRCs with MSI have distinct clinicopathological characteristics with pronounced tumor-associated immune responses. The aim of our study was to investigate the intensity of host immune response in CRC tissue by comparing microsatellite stable (MSS) and instable tumors. Methods: The study was performed on CRC specimens from 28 patients with MSI and compared with 30 MSS tumors. The microsatellite status was evaluated with two markers by PCR and melting point analysis. The immunostaining with anti-CD3 pan-T cell antibody was used to quantify the number of tumor infiltrating lymphocytes. The lymphocytes in peritumoral stromal and the Crohn?s-like peritumoral reaction were counted on H&E slides. Results: No significant differences were found in the average number of lymphocytes in peritumoral stroma and in clinicopathological characteristics of CRCs. The conspicuous Crohn?s-like lymphoid reactions were present in 67.86% of CRCs with MSI versus 26.66% of MSS cases. The CRCs with MSI cases carried significantly higher numbers of tumor infiltrating T-lymphocytes (13.21 versus 7.47) (p<0.0001). Conclusion: The presences of peritumoral Crohn?s-like lymphoid and intraepithelial lymphocytic reaction were intensive markers for MSI in colorectal carcinomas in our study. The peculiar genetic instability in MSI tumors may lead to a continuous production of abnormal peptides, which act as neoantigens. They could induce specific antitumor immune responses effective in limiting tumor growth and spread. Abnormal peptides are potentially promising in immunotherapy advancing and in the design of a vaccine against colorectal tumors with MSI.