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Background & Aims Fifty percent of colorectal cancers show elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) and are associated with inflammation, metastasis, and poor patient outcome. EMAST results from interleukin 6–induced nuclear-to-cytosolic displacement of the DNA mismatch repair protein Mutated S Homolog 3, allowing frameshifts of dinucleotide and tetranucleotide but not mononucleotide microsatellites. Unlike mononucleotide frameshifts that universally shorten in length, we previously observed expansion and contraction frameshifts at tetranucleotide sequences. Here, we developed cell models to assess tetranucleotide frameshifts in real time. Methods We constructed plasmids containing native (AAAG)18 and altered-length ([AAAG]15 and [AAAG]12) human D9S242 locus that placed enhanced green fluorescent protein +1 bp/-1 bp out-of-frame for protein translation and stably transfected into DNA mismatch repair–deficient cells for clonal selection. We used flow cytometry to detect enhanced green fluorescent protein–positive cells to measure mutational behavior. Results Frameshift mutation rates were 31.6 to 71.1 × 10-4 mutations/cell/generation and correlated with microsatellite length (r2 = 0.986, P = .0375). Longer repeats showed modestly higher deletion over insertion rates, with both equivalent for shorter repeats. Accumulation of more deletion frameshifts contributed to a distinct mutational bias for each length (overall: 77.8% deletions vs 22.2% insertions), likely owing to continual deletional mutation of insertions. Approximately 78.9% of observed frameshifts were 1 AAAG repeat, 16.1% were 2 repeats, and 5.1% were 3 or more repeats, consistent with a slipped strand mispairing mutation model. Conclusions Tetranucleotide frameshifts show a deletion bias and undergo more than 1 deletion event via intermediates, with insertions converted into deletions. Tetranucleotide markers added to traditional microsatellite instability panels will be able to determine both EMAST and classic microsatellite instability, but needs to be assessed by multiple markers to account for mutational behavior and intermediates., Graphical abstract

The calcium sensing receptor (CaSR) is functionally expressed in normal human pancreases, but its pathological role in pancreatic tumorigenesis is currently unknown. We sought to investigate the role of CaSR in pancreatic cancer (PC) and the underlying molecular mechanisms. We revealed that the expression of CaSR was consistently downregulated in the primary cancer tissues from PC patients, which was correlated with tumor size, differentiation and poor survival of the patients. CaSR activation markedly suppressed pancreatic tumorigenesis in vitro and in vivo likely through the Ca(2+) entry mode of Na(+)/Ca(2+) exchanger 1 (NCX1) to induce Ca(2+) entry into PC cells. Moreover, NCX1-mediated Ca(2+) entry resulted in Ca(2+)-dependent inhibition of β-catenin signaling in PC cells, eventually leading to the inhibition of pancreatic tumorigenesis. Collectively, we demonstrate for the first time that CaSR exerts a suppressive function in pancreatic tumorigenesis through a novel NCX1/Ca(2+)/β-catenin signaling pathway. Targeting this specific signaling pathway could be a potential therapeutic strategy for PC.

Background & Aims Molecular events that lead to recurrence and/or metastasis after curative treatment of patients with colorectal cancers (CRCs) are poorly understood. Patients with stage II or III primary CRC with elevated microsatellite alterations at selected tetranucleotide repeats and low levels of microsatellite instability (E/L) are more likely to have disease recurrence after treatment. Hypoxia and/or inflammation not only promote metastasis, but also induce elevated microsatellite alterations at selected tetranucleotide repeats by causing deficiency of MSH3 in the cancer cell nucleus. We aimed to identify genetic alterations associated with metastasis of primary colorectal tumors to liver and to determine their effects on survival. Methods We obtained 4 sets of primary colorectal tumors and matched liver metastases from hospitals in Korea and Japan. Intragenic microsatellites with large repeats at 141 loci were examined for frame-shift mutations and/or loss of heterozygosity (LOH) as possible consequences of MSH3 deficiency. Highly altered loci were examined for association with E/L in liver metastases. We analyzed data from 156 of the patients with stage II or III primary colorectal tumors to determine outcomes and whether altered loci were associated with E/L. Results LOH at several loci at chromosome 9p24.2 (9p24.2-LOH) was associated with E/L in liver metastases (odds ratio = 10.5; 95% confidence interval: 2.69−40.80; P = .0007). We found no significant difference in the frequency of E/L, 9p24.2-LOH, mutations in KRAS or BRAF , or the combination of E/L and 9p24.2-LOH, between primary colorectal tumors and their matched metastases. Patients with stage II or III colorectal tumors with E/L and 9p24.2-LOH had increased survival after CRC recurrence (hazard ratio = 0.25; 95% CI: 0.12−0.50; P = .0001), compared with patients without with E/L and 9p24.2-LOH. E/L with 9p24.2-LOH appeared to be an independent prognostic factor for overall survival of patients with stage III CRC (hazard ratio = 0.06; 95% CI: 0.01−0.57; P = .01). Conclusions E/L with 9p24-LOH appears to be a biomarker for less aggressive metastasis from stage III primary colorectal tumors.

Over the past three decades since molecular analyses of somatic gene alterations in primary human cancer specimens first became tractable, many of the recurrent somatic genetic and epigenetic defects present in colorectal cancers (CRCs) have been identified. The accumulation of multiple loss-of-function defects in selected tumor suppressor genes and gain-of-function defects in selected oncogenes, together with epigenetic alterations, such as DNA methylation changes, is believed to be critical in initiating colorectal tumorigenesis and the progression of dysplastic precursors to invasive and ultimately metastatic lesions (1–4). Among the most common tumor suppressor gene mutations in CRCs are those in the APC (adenomatous polyposis coli) and TP53 genes (2–4). The most common oncogene mutations in CRC include point mutations activating the functions of the KRAS, PI3KCA (phosphoinositide-3-kinase, catalytic, alpha polypeptide), BRAF, and NRAS proteins (2–4). The oncogene missense mutations found in the KRAS and NRAS genes in about 40–45% of CRCs most commonly affect codons 12 and 13, but a subset of CRCs have KRAS or NRAS colon 61 missense mutations (2, 3). Substitution of glutamic acid for the wild type valine at codon 600 (V600E) accounts for the vast majority of BRAF activating mutations in CRC (2, 3). Mutations activating KRAS or NRAS are mutually exclusive with BRAF activating mutations (2–4).

Colon cancer develops and progresses as a consequence of abnormal cellular molecular changes, many of which result in mutant DNA. Modern molecular techniques allow examination of individual patient genetic data that ascribe risk, predict outcome, and/or modify an approach to therapy. DNA testing and molecular screening are in use today and are becoming a critical and necessary part of routine patient care. Assessing at-risk patients for hereditary colon cancer is predicted to move from individual gene testing that is commonly performed today to whole exome or whole genome sequencing, providing additional vast information of the patient's genome that might not be related to the colon cancer syndrome. Detecting mutant DNA from shed tumor cells in fecal material for colon cancer screening will increase in diagnostic accuracy over time, with improvements in the panel of mutant DNA being examined and through clinical testing. DNA mutations and other molecular changes detected directly from within the colon cancer help to inform and guide the physician for the best approach for optimal patient care and outcome. The use of epidermal growth factor receptor-targeted therapy in advanced colon cancer patients requires knowledge of the mutation status for KRAS and BRAF genes, and knowing the mutational status of PIK3CA may predict how patients respond to aspirin to prevent colon cancer recurrence. Biologically driven decision-making, or precision medicine, is becoming increasingly adopted for optimal care and outcome for colon cancer patients. Gastroenterologists will need to be increasingly aware.

Colorectal cancer (CRC) burden is not equal among populations in the United States. African Americans have the highest CRC incidence and mortality of all US populations, and rates are not decreasing to the levels of non-Hispanic Whites.1 In addition to increased cancer risk, adenoma risk is also higher in African Americans, and both adenomas and cancers occur more frequently in the proximal colon and at younger ages in African Americans.2 Reasons for population differences are multifactorial and include differences in tumor biology and behavior, genetic risk, access to health care, and screening rates.3,4 As demonstrated by the Delaware CRC screening program, strategies to maximize screening hold significant promise for correcting CRC disparities.5 Current US Multisociety Task Force guidelines recommend CRC screening for all populations at average risk beginning at age 50 years, and individuals at increased risk (such as those with family history, inherited genetic syndromes or inflammatory bowel disease) are recommended to begin screening earlier.6 Owing to increased and earlier neoplasia risk, some professional organizations recommend screening in African Americans starting at age 45.3 Others raise concerns about the impact of complicating existing standardized guidelines and the unclear benefit of earlier age screening in African Americans despite an increased proportion of CRC under the age of 50 years. They recommend that efforts should focus instead on improving screening efforts in African Americans starting at age 50. Given this controversy, it is timely to examine how our profession can take the lead in reducing CRC disparities among African Americans. Several strategies should be considered when prioritizing our efforts (Table 1). Table 1 Strategies to Decrease Disparities in Colorectal Cancer (CRC) Among African Americans (AAs) African Americans are less knowledgeable about CRC and screening guidelines compared with Caucasians,7 and are less likely to transmit a family history of cancer.4 Both lack of knowledge about screening benefits and fatalistic views about cancer are associated with reduced likelihood of screening among African Americans.8 Interventions designed to educate patients about CRC and screening guidelines can improve screening rates and attitudes,9,10 and those that contain culturally sensitive materials have been shown to boost screening among African Americans.9 These and other studies suggest that lack of knowledge about CRC screening benefits is a surmountable barrier, but challenges remain. For example, ≤40% of African Americans aged 65 years and older in some US areas are estimated to read below a 5th-grade level,9 limiting the use of some CRC screening materials. In addition, standardized patient education approaches may not work in all populations and age groups, potentially necessitating individualized interventions and inclusion of personnel to engage in community-based education and outreach. The impact of provider endorsement on screening rates cannot be under-estimated. Lack of provider recommendation is an important barrier to screening in African Americans.11 However, studies that evaluate the impact of provider education on CRC screening in African Americans are lacking. Continuing medical education seminars can increase CRC knowledge, but whether this translates to improved screening rates is not clear.12 Just as there are no standardized approaches for patient education, there are no standardized strategies to improve provider education. Moreover, providers cite insufficient time as a barrier to recommending CRC screening to patients,13 potentially causing additional delay in timely CRC screening for this higher risk population. Strategies focused on physician education about the increased CRC burden among African Americans may improve CRC screening, but more research is needed to demonstrate this. Patient navigation is a proven strategy for increasing CRC screening rates in African Americans and also improves no show rates and bowel preparation.3,14 A randomized trial in older African Americans of phone navigation and printed material versus printed material alone found a 53% increase in endoscopic screening in the navigation group with health literate subjects showing a stronger effect from navigation.14 Financial modeling based on a program in New York City found patient navigation to be cost effective,15 whereas a randomized trial noted greater costs for tailored navigation.16 Implementation of patient navigation from research studies into the “real world” can be complex and requires flexibility and cooperation among stakeholders.17 Thus, although patient navigation can increase screening among African Americans, logistics and cost are major barriers to widespread adoption. Efforts should focus on overcoming these barriers through education, research, and advocacy for patient navigation in CRC screening. A more controversial strategy is to lower the initial screening age recommendation for African Americans. Arguments supporting this strategy include increased rates of significant neoplasia, higher stage of CRC at younger ages, and proximal location of tumors among African Americans.3 Lieberman et al2 showed that the rate of high risk polyps (>9 mm) was increased 17%–38% in African American men ages 50-69 years and 25%– 50% in African American women ages 50-64 years compared with Caucasian men and women in these age groups. Although the risk of large polyps was not statistically different for African American men and women

The discipline of gastroenterology, hepatology and pancreatology has changed dramatically since its inception as a specialty of internal medicine. The specialty originally focused and pursued an understanding of the pathology and physiology of the gastrointestinal tract, liver and pancreas scientifically, something which is still in active evolution.. We began to comprehend gut motility, stomach acid secretion, the epidemiology of digestive cancers, autoimmune diseases of the gut, pancreas and liver, and how infectious diseases are transmitted and affect the GI tract. Treatment slowly became possible with the acquired knowledge, and created approaches for therapeutics. Histamine type 2 blockers and proton pump inhibitors, nucleotide and nucleoside analogs, immune modulators, and a myriad of antibiotics have been studied and used effectively to alleviate patient suffering from GI diseases. Radiological imaging helped determine the absence, presence, or extent of disease non-invasively. Endoscopy of the alimentary tract and its related growing list of special devices have provided a huge leap forward in caring for patients with GI disease, allowing direct visualization of and sampling from the GI tract, and providing an avenue for direct therapeutic intervention. We have now entered the genomic era, providing another leap forward in the care of patients with GI diseases. This era commenced with the identification genetic mutations as the basis of Mendelian-inherited diseases involving the GI tract, such as familial adenomatous polyposis [1,2], cystic fibrosis [3–5], and genetic hemochromatosis [6]. The genetic information could be predictive if one carried the mutation; it could be also be predictive to family members when they did not carry the mutation, foregoing unnecessary surveillance efforts and applying those healthcare resources aptly to mutant carriers. Genetic information has progressed dramatically and now extends past heritable diseases; it applies to many GI conditions in terms of risk (e.g. genome wide association studies or GWAS, or the presence or absence of a mutation directly within tumor tissue), prediction of biological behavior, outcome and survival, and in the approach and use of therapeutics (e.g. cetuximab in wild type KRAS colorectal cancer, or 6-thioguanine and 6-methylmercaptopurine metabolite levels for optimal use of azathioprine or 6-mercaptopurine). The field is rapidly evolving. A convergence of advancing knowledge of GI tract disease, technical advances and reduced costs for next generation sequencing and other analytic technologies such as proteomics and metabolomics, easier access to sampling human tissue with advances in image-directed biopsies and minimally invasive tissue removal, and a growing number of interventions discovered to improve the health of patients with GI diseases make this era an exciting time for helping our patients and fundamentally changing our GI practices. Biomarkers are a key part of precision (personalized or individualized) medicine. Molecular biomarkers are derived from the genetic, genomic and other high-throughput platforms in analysis of blood, tissue, fecal, urine or other biological material that can inform the practitioner on the next best course of action for the individual patient [7]. Biomarkers ideally lead to prescriptive targeted treatment changes that can improve the outcome of patients with GI disease; this is the essence and part of the definition of precision medicine [8]. Biomarkers can also be diagnostic or prognostic, being more informative for a clinical course rather than a targeted individualized treatment prescription. The assumption and reality is that GI patients with a specific disease are biologically heterogeneous, and molecular biomarkers can differentiate patients into subtype groupings of more homogeneous individuals sharing an actionable characteristic amenable to molecularly targeted therapies beneficial to that subgroup or individual. Both biomarkers and targeted individualized therapies are the cornerstone of President Obama’s Precision Medicine Initiative put forth in early 2015 [9]. This initiative aims to further revolutionize the practice of medicine by generating additional scientific evidence to move the concept of precision medicine into everyday clinical practice. Parallel and complimentary ventures such as the 100,000 Genomes Project in the UK aim to identify novel genetic diagnoses and create opportunities for the use of genomics in healthcare [10]. This special issue of Gastroenterology lays a foundation and provides a current understanding to the approach to precision medicine for several GI disorders, a timely topic given the growing international investments in personalized care. We as editors of this special issue, along with the entire Gastroenterology Board of Editors, selected the topic of genetics, genetic testing, and biomarkers in digestive diseases because of the rapid advances in these topics among the GI diseases over just the past few years. Recent studies outlined in many of the articles within this special issue highlight how fast information has moved, and how quick biomarkers and potential therapeutic targets for treatment purposes are lining up for phased human clinical studies, pharmaceutical testing portfolios, and routine patient use. The transformation from bench to practice has been greatly accelerated with newer and cheaper genomic analytic capabilities and information technologies, and rapid dissemination of information. New molecular biomarker tests are being put out to the clinical commercial market on a regular basis. Many aspects of this rapid change have and will continue to become part of daily clinical GI practice. For this special issue of Gastroenterology, we recruited leading authorities to update our readers in the genetics, genetic testing, and biomarkers of digestive diseases. The 12 reviews and 2 commentaries in this issue cover many aspects of the GI tract, hepatobiliary system and pancreas. The two commentaries are more general than disease-focused, and deal with the generation and recording of genetic information. The commentary by Ananthakrishnan and Lieberman examines the current and future ideal use of electronic health records for genetic and biomarker information that pertains to the practitioner and researcher, laboratory, and patient [11]. Ngeow and Eng’s commentary addresses a path forward in the post-genomic area, including the examination of gene-gene or gene-environment interactions, and clinical implementation of genomics [12]. Among the 12 disease-focused reviews, four articles examine biomarkers and genetics and their clinical application in colorectal cancer (CRC). Stoffel and Boland provide genetic testing insights in inherited forms of CRC [13], and Carethers and Jung highlight the genetics and potential biomarkers for use in patients with sporadic CRC [14]. Okugawa, Grady and Goel showcase how epigenetic alterations in CRC provide biomarkers for patient care [15], and Robertson and Imperiale review the clinical application of biomarkers within stool tests for CRC screening [16]. Three articles focus on the rapidly advancing use of genetics and biomarkers for inflammatory bowel disease (IBD). McGovern, Kugathasan and Cho provide an update on GWAS data from large IBD studies [17], Dubinsky and Braun showcase the use of microbial biomarkers for IBD diagnosis [18], and Sands highlights inflammatory biomarkers for IBD [19]. Two articles focus on the liver: Pietrangelo reviews classic hemochromatosis genetics and testing [20], and Zucman-Rossi, Villaneuva, Nault and Llovet provide a comprehensive review of the genetics and biomarkers for hepatocellular carcinoma [21]. The remaining three reviews highlight the esophagus, stomach, and pancreas. Reid, Paulson and Li present the most up-to-date genetic analyses of Barrett’s esophagus and esophageal adenocarcinoma [22]. Tan and Yeoh supply the latest insights of the genetics of gastric adenocarcinoma [23], while Whitcomb, Shelton and Brand present the latest on the biomarkers and genetics of inherited and sporadic forms of pancreatic cancer [24]. We are very grateful to the contributing authors as well as the insightful manuscript reviewers and editorial staff for their time and energy in creating these outstanding articles with useful figures and tables for the readers of Gastroenterology. We hope that readers of this special issue of Gastroenterology will find it full of new insights into this rapidly moving field in clinical GI practice. We hope you enjoy the up-to-date information, and see the alignment with current and future aspects of the Precision Medicine Initiative and the other related global efforts. We trust that this issue provides a new and timely reference as precision medicine, biomarkers, and genetics move more fully into GI clinics to direct patient care.

Mucosal immunology lost one of its true pioneers when Marty Kagnoff succumbed to complications of pancreatic cancer on 16 November 2014 at his home in La Jolla, California. He was 73. However, his influence on the field—particularly as personified by the almost 100 students, fellows, and junior faculty members that he was directly responsible for training—will be felt for generations.

Colorectal cancer arises as a consequence of the accumulation of genetic alterations (gene mutations, gene amplification, and so on) and epigenetic alterations (aberrant DNA methylation, chromatin modifications, and so on) that transform colonic epithelial cells into colon adenocarcinoma cells. The loss of genomic stability and resulting gene alterations are key molecular pathogenic steps that occur early in tumorigenesis; they permit the acquisition of a sufficient number of alterations in tumor suppressor genes and oncogenes that transform cells and promote tumor progression. Two predominant forms of genomic instability that have been identified in colon cancer are microsatellite instability and chromosome instability. Substantial progress has been made to identify causes of chromosomal instability in colorectal cells and to determine the effects of the different forms of genomic instability on the biological and clinical behavior of colon tumors. In addition to genomic instability, epigenetic instability results in the aberrant methylation of tumor suppressor genes. Determining the causes and roles of genomic and epigenomic instability in colon tumor formation has the potential to yield more effective prevention strategies and therapeutics for patients with colorectal cancer.

Objective : Squamous cell cancer of the anus is associated with multiple risk factors, including infection with human papillomavirus, immunosuppression, chronic inflammation, and tobacco smoking, although there is little data on these factors for the prediction of recurrent disease. Here, we evaluated the risk of recurrence and mortality of anal carcinoma in association with tobacco smoking. Methods : We conducted a retrospective review of cases of anal carcinoma from two local hospitals. We obtained information on treatment response and cancer recurrence, as well as tobacco usage from medical records. Results : We identified 64 patients with squamous cell cancer of the anus, and 34 of these (53%) had a tobacco smoking history. Current smokers had higher carcinoma recurrence rates (11/34, 32%) than non-smokers (6/30, 20%). Overall mortality was 33% (21/64), and cancer-related mortality was 23% (15/64). Smokers were more likely to die from recurrence than non-smokers, with 45% of smokers dead compared to only 20% of non-smokers by 5 years after treatment. Conclusion : Tobacco smoking appears to be associated with anal carcinoma disease recurrence, and is related to increased mortality. This data suggests that patients should be cautioned about tobacco smoking once a diagnosis of anal carcinoma is made in attempt to improve their long-term outcome.

DCC and UNC5C, Netrin-1 dependence receptors, perform an important role in intestinal epithelial biology. Both receptors frequently are down-regulated in colorectal cancer (CRC). Although CRCs frequently lose DCC owing to deletions at 18q, the mechanism for the UNC5C loss is poorly understood. We hypothesized that UNC5C is silenced epigenetically in CRC, and that there are interactions between losses of UNC5C and DCC in colorectal tumorigenesis.Gene expression and epigenetic analysis of UNC5C was examined in 8 CRC cell lines, 147 sporadic CRCs with corresponding normal mucosa, and 52 adenomatous polyps (APs). Allelic imbalances at DCC were determined in CRCs. The molecular analyses were compared with genetic and clinicopathologic features.All CRC cell lines showed UNC5C methylation and an associated loss of gene expression. Treatment with 5-Aza-2'-deoxycytidine resulted in restoration of gene transcription. UNC5C methylation was significantly higher in CRCs (76.2%) and APs (63.5%) than in corresponding normal mucosa (6%; P.0001). Allelic imbalance at DCC was observed in 61% of CRCs. Overall, 89.3% of CRCs had alterations of one of the dependence receptors. UNC5C methylation occurred predominantly in the earlier lesions (APs and early CRCs), whereas DCC losses were more often in advanced CRCs.The majority of CRCs harbor defects in Netrin-1 receptors, emphasizing the importance of this growth regulatory pathway in cancer. Furthermore, the timing of the molecular alterations in the Netrin-1 receptors is not random because UNC5C inactivation occurs early, whereas DCC losses occurs in later stages of multistep colorectal carcinogenesis.

Background & Aims: Colon cancers with high-frequency microsatellite instability (MSI-H) develop frameshift mutations in tumor suppressors as part of their pathogenesis. ACVR2 is mutated at its exon 10 polyadenine tract in >80% of MSI-H colon cancers, coinciding with loss of protein. ACVR2 transmits the growth effects of activin via phosphorylation of SMAD proteins to affect gene transcription. The functional effect of activin in colon cancers has not been studied. We developed and characterized a cell model in which we studied how activin signaling affects growth. Methods: hMLH1 and ACVR2 mutant HCT116 cells were previously stably transferred with chromosome 2 (HCT116+chr2), restoring a single regulated copy of wild-type ACVR2 but not hMLH1. Both HCT116+chr2 and parental HCT116 cells (as well as HEC59 and ACVR2 and hMSH2 complemented HEC59+chr2 cells) were assessed for genetic complementation and biologic function. Results: HCT116+chr2 cells and HEC59+chr2 cells, but not ACVR2-mutant HCT116 or HEC59 cells, acquired wild-type ACVR2 as well as expression of ACVR2 wild-type messenger RNA. Complemented ACVR2 protein complexed with ACVR1 with activin treatment, generating nuclear phosphoSMAD2 and activin-specific gene transcription. ACVR2-restored cells showed decreased growth and reduced S phase but increased cellular migration following activin treatment. ACVR2 small interfering RNA reversed these effects in complemented cells. Conclusions: ACVR2-complemented MSI-H colon cancers restore activin-SMAD signaling, decrease growth, and slow their cell cycle following ligand stimulation but show increased cellular migration. Activin is growth suppressive and enhances migration similar to transforming growth factor β in colon cancer, indicating that abrogation of the effects of activin contribute to the pathogenesis of MSI-H colon cancers.

Gastrointestinal cancer has attracted the attention of many basic scientists and clinical investigators over the past 2‐3 decades, and the progress made is currently being translated into new types of clinical management for our patients. This review will focus on colorectal cancer, highlight some of the newer findings that are available, and attempt to predict where future breakthroughs are likely to occur. Drug interventions directed at established cancer and novel preventive programs will be highlighted; patients are increasingly interested in understanding how they can prevent cancers in both high-risk and ordinary-risk situations. General Management Strategies for Gastrointestinal Cancer The gastrointestinal tract represents the interface with our diet. We should be mindful that the digestive organs account for more cancer than any other system. A key message is that manipulation of diet, gut flora, and the gastrointestinal milieu are reasonable targets to modify the risk of cancer in the gastrointestinal tract. Our approaches to the management of cancer and cancer risk might be broadly divided into the following categories. At the preventive end of the spectrum, we try to identify healthy people who are at increased risk for cancer and intervene with treatment programs that will prevent neoplastic lesions from developing. Some individuals who are completely healthy may approach us and ask how to reduce their risk of cancer. In the near future, we may be asked to develop cancer prevention programs

Background & Aims: The DNA mismatch repair (MMR) system recognizes certain DNA adducts caused by alkylation damage in addition to its role in recognizing and directing repair of interstrand nucleotide mismatches and slippage mistakes at microsatellite sequences. Because defects in the MMR system can confer tolerance to acquired DNA damage and, by inference, the toxic effects of certain chemotherapeutic agents, we investigated the effect of 5-fluorouracil (5-FU) on colon cancer cell lines. Methods: We determined growth selection by cell enrichment assay and cloning efficiency after treatment with 5 μmol/L 5-FU, assayed nucleic 3 H–5-FU incorporation, and analyzed the cell cycle by flow cytometry. Results: 5-FU treatment provided a growth advantage for MMR-deficient cell lines, indicating a relative degree of tolerance to 5-FU by the MMR-deficient cell lines. Enhanced survival was statistically significant after 5 days of growth, and a 28-fold reduction in survival was noted in the MMR-proficient cells by clonagenic assays after 10 days of growth. Differences in nucleotide uptake of 5-FU did not account for the observed growth differences, and specific cell cycle checkpoint arrest was not detected. Conclusions: Intact DNA MMR seems to recognize 5-FU incorporated into DNA but may do so in a different manner than other types of alkylation damage. Defective DNA MMR might be one mechanism for tumor resistance to 5-FU. GASTROENTEROLOGY 1999;117:123-131

Background & Aims: Allelic loss of a portion of chromosome 18q and lack of expression of deleted in colorectal cancer (DCC) protein has been reported as an adverse prognostic indicator for stage II (i.e., Dukes' B2) colorectal cancer. Our aim was to assess whether the DCC gene locus was responsible. Methods: We amplified five DNA microsatellite markers located on chromosome 18q21 surrounding or within the DCC gene locus, including a DCC intragenic (TA) n microsatellite, from DNA microdissected and isolated from paraffin-embedded, formalin-fixed specimens of 70 patients with stage II colorectal cancer. Epidemiological and survival data were blinded from the microsatellite analysis to avoid bias. Results: The average follow-up time was 63.3 months for all patients. Eleven patients died of colorectal cancer by the end of the study. Loss of heterozygosity of 18q21 was present in 30 of 70 (43%) tumors. After adjustment for all other evaluated factors, 18q21 allelic loss was not a predictor of survival (hazard ratio, 1.17; 95% confidence interval, 0.27–5.10; P = 0.84). Conclusions: Loss of heterozygosity of 18q21 does not seem to predict a survival disadvantage in stage II colorectal cancer in our patient population, and its proposed use as a prognosticator of survival or chemotherapy stratification marker for stage II tumors is not substantiated. GASTROENTEROLOGY 1998;114:1188-1195

The development of colorectal neoplasia originates from normal colonic mucosa, progresses to the adenomatous polyp, and later may evolve into carcinoma. This procession of histologic change can be defined by a series of successive waves of clonal expansion that contain certain genetic alterations. These genetic alterations include mutations in the K-ras oncogene and mutation in the one allele coupled with loss of the second allele for the tumor suppressor genes APC, DCC, and p53. The normal forms of these genes encode for proteins that regulate cell growth, cell-to-cell adhesion, and cell cycle checkpoints. Information on the function of these genes, as well as a proposed model of sequential mutation and loss of these regulatory genes during colorectal tumorigenesis are presented.

Background & Aims : Hereditary nonpolyposis colorectal cancer (HNPCC) has been linked recently to a defect in repairing mismatched nucleotides in DNA. The aim of this study was to screen for germline mutations that result in prematurely truncated proteins in two of the mismatch repair genes identified at this time, hMLH1 and hMSH2, in a consecutive series of patients belonging to familial aggregations of colorectal cancer. Methods : Nineteen individuals with colorectal cancer from 19 families were consecutively referred because of a strong positive family history of colorectal cancer. Premature truncation mutations in hMLH1 and hMSH2 were sought from lymphocyte RNA by using an in vitro transcription/translation (IVTT) assay. Results : Protein truncating mutations in the hMLH1 or hMSH2 genes were found in 50% of families with HNPCC (6 of 12) but were not observed in any of the remaining familial aggregations that did not fulfill the standard criteria for HNPCC. In some of the IVTT-positive samples, the mutations were characterized by genomic sequencing. Conclusions : IVTT may be a practical method to accomplish primary screening of germline mutations in DNA mismatch repair genes in HNPCC; however, a broader approach is necessary to obtain a more complete picture of the mutational spectrum in HNPCC and other familial aggregations of colorectal cancer.