Serendipity Strikes: How Pursuing Novel Hypotheses Shifted the Paradigm Regarding the Genetic Basis of Colorectal Cancer and Changed Cancer Therapy.

In this installment of the "Paradigm Shifts in Perspective" series, the authors, all scientists who have been involved in colorectal cancer (CRC) research for most or all of their careers, have watched the field develop from early pathological descriptions of tumor formation to the current understanding of tumor pathogenesis that informs personalized therapies. We outline how our understanding of the pathogenetic basis of CRC began with seemingly isolated discoveries-initially with the mutations in RAS and the APC gene, the latter of which was initially found in the context of intestinal polyposis, to the more complex process of multistep carcinogenesis, to the chase for tumor suppressor genes, which led to the unexpected discovery of microsatellite instability (MSI). These discoveries enabled the authors to better understand how the DNA mismatch repair (MMR) system not only recognizes DNA damage but also responds to damage by DNA repair or by triggering apoptosis in the injured cell. This work served, in part, to link the earlier findings on the pathogenesis of CRC to the development of immune checkpoint inhibitors, which has been transformative-and curative-for certain types of CRCs and other cancers as well. These discoveries also highlight the circuitous routes that scientific progress takes, which can include thoughtful hypothesis testing and at other times recognizing the importance of seemingly serendipitous observations that substantially change the flow and direction of the discovery process. What has happened over the past 37 years was not predictable when this journey began, but it does speak to the power of careful scientific experimentation, following the facts, perseverance in the face of opposition, and the willingness to think outside of established paradigms.

A Liquid Biopsy Signature for the Detection of Patients With Early-Onset Colorectal Cancer.

BACKGROUND & AIMS: Early-onset colorectal cancer (EOCRC) is a distinct clinical and molecular entity with poor survival outcomes compared with late-onset CRC. Although the incidence of EOCRC is rising, current CRC screening strategies have several limitations in diagnostic performance for EOCRC. In view of this clinical challenge, novel and robust biomarkers for detection of EOCRC are necessary. The aim of this study was to develop a circulating micro RNA (miRNA) signature for the diagnosis of patients with EOCRC. METHODS: A systematic discovery approach by analyzing a large, publicly available, noncoding RNA expression profiling dataset (GSE115513) was used. A panel of miRNAs was identified, which was subsequently validated in blood samples from patients with EOCRC in 2 independent cohorts (n = 149) compared with controls (n = 110) and pre/postoperative plasma specimens (n = 22) using quantitative reverse-transcription polymerase chain reaction assays. RESULTS: In the discovery phase, 4 miRNAs were found to be expressed in blood samples. A combination signature of these 4 miRNAs (miR-193a-5p, miR-210, miR-513a-5p, and miR-628-3p) yielded an area under the curve of 0.92 (95% confidence interval, 0.85-0.96) for identification of EOCRC in the training cohort. The miRNA panel performance was then confirmed in an independent validation cohort (area under the curve, 0.88; 95% confidence interval, 0.82-0.93). Moreover, the miRNA panel robustly identified patients with early-stage EOCRC (P < .001). The decreased expression of miRNAs in postsurgery plasma specimens indicated their tumor specificity. CONCLUSIONS: Our novel miRNA signature for the diagnosis of EOCRC has the potential to identify patients with EOCRC with high accuracy for clinical application in the noninvasive diagnosis of EOCRC.

Diagnosis and Management of Cancer Risk in the Gastrointestinal Hamartomatous Polyposis Syndromes: Recommendations From the US Multi-Society Task Force on Colorectal Cancer.

The gastrointestinal hamartomatous polyposis syndromes are rare, autosomal dominant disorders associated with an increased risk of benign and malignant intestinal and extraintestinal tumors. They include Peutz-Jeghers syndrome, juvenile polyposis syndrome, the PTEN hamartoma tumor syndrome (including Cowden's syndrome and Bannayan-Riley-Ruvalcaba syndrome), and hereditary mixed polyposis syndrome. Diagnoses are based on clinical criteria and, in some cases, confirmed by demonstrating the presence of a germline pathogenic variant. The best understood hamartomatous polyposis syndrome is Peutz-Jeghers syndrome, caused by germline pathogenic variants in the STK11 gene. The management is focused on prevention of bleeding and mechanical obstruction of the small bowel by polyps and surveillance of organs at increased risk for cancer. Juvenile polyposis syndrome is caused by a germline pathogenic variant in either the SMAD4 or BMPR1A genes, with differing clinical courses. Patients with SMAD4 pathogenic variants may have massive gastric polyposis, which can result in gastrointestinal bleeding and/or protein-losing gastropathy. Patients with SMAD4 mutations usually have the simultaneous occurrence of hereditary hemorrhagic telangiectasia (juvenile polyposis syndrome-hereditary hemorrhagic telangiectasia overlap syndrome) that can result in epistaxis, gastrointestinal bleeding from mucocutaneous telangiectasias, and arteriovenous malformations. Germline pathogenic variants in the PTEN gene cause overlapping clinical phenotypes (known as the PTEN hamartoma tumor syndromes), including Cowden's syndrome and related disorders that are associated with an increased risk of gastrointestinal and colonic polyposis, colon cancer, and other extraintestinal manifestations and cancers. Due to the relative rarity of the hamartomatous polyposis syndromes, recommendations for management are based on few studies. This US Multi-Society Task Force on Colorectal Cancer consensus statement summarizes the clinical features, assesses the current literature, and provides guidance for diagnosis, assessment, and management of patients with the hamartomatous polyposis syndromes, with a focus on endoscopic management.

Aspirin's effect on kinetic parameters of cells contributes to its role in reducing incidence of advanced colorectal adenomas, shown by a multiscale computational study.

Aspirin intake has been shown to lead to significant protection against colorectal cancer, for example with an up to twofold reduction in colorectal adenoma incidence rates at higher doses. The mechanisms contributing to protection are not yet fully understood. While aspirin is an anti-inflammatory drug and can thus influence the tumor microenvironment, in vitro and in vivo experiments have recently shown that aspirin can also have a direct effect on cellular kinetics and fitness. It reduces the rate of tumor cell division and increases the rate of cell death. The question arises whether such changes in cellular fitness are sufficient to significantly contribute to the epidemiologically observed protection. To investigate this, we constructed a class of mathematical models of in vivo evolution of advanced adenomas, parameterized it with available estimates, and calculated population level incidence. Fitting the predictions to age incidence data revealed that only a model that included colonic crypt competition can account for the observed age-incidence curve. This model was then used to predict modified incidence patterns if cellular kinetics were altered as a result of aspirin treatment. We found that changes in cellular fitness that were within the experimentally observed ranges could reduce advanced adenoma incidence by a sufficient amount to account for age incidence data in aspirin-treated patient cohorts. While the mechanisms that contribute to the protective effect of aspirin are likely complex and multi-factorial, our study demonstrates that direct aspirin-induced changes of tumor cell fitness can significantly contribute to epidemiologically observed reduced incidence patterns.

Diagnosis and management of cancer risk in the gastrointestinal hamartomatous polyposis syndromes: recommendations from the U.S. Multi-Society Task Force on Colorectal Cancer.

The gastrointestinal hamartomatous polyposis syndromes are rare, autosomal dominant disorders associated with an increased risk of benign and malignant intestinal and extraintestinal tumors. They include Peutz-Jeghers syndrome, juvenile polyposis syndrome, the PTEN hamartoma tumor syndrome (including Cowden's syndrome and Bannayan-Riley-Ruvalcaba syndrome), and hereditary mixed polyposis syndrome. Diagnoses are based on clinical criteria and, in some cases, confirmed by demonstrating the presence of a germline pathogenic variant. The best understood hamartomatous polyposis syndrome is Peutz-Jeghers syndrome, caused by germline pathogenic variants in the STK11 gene. The management is focused on prevention of bleeding and mechanical obstruction of the small bowel by polyps and surveillance of organs at increased risk for cancer. Juvenile polyposis syndrome is caused by a germline pathogenic variant in either the SMAD4 or BMPR1A genes, with differing clinical courses. Patients with SMAD4 pathogenic variants may have massive gastric polyposis, which can result in gastrointestinal bleeding and/or protein-losing gastropathy. Patients with SMAD4 mutations usually have the simultaneous occurrence of hereditary hemorrhagic telangiectasia (juvenile polyposis syndrome-hereditary hemorrhagic telangiectasia overlap syndrome) that can result in epistaxis, gastrointestinal bleeding from mucocutaneous telangiectasias, and arteriovenous malformations. Germline pathogenic variants in the PTEN gene cause overlapping clinical phenotypes (known as the PTEN hamartoma tumor syndromes), including Cowden's syndrome and related disorders that are associated with an increased risk of gastrointestinal and colonic polyposis, colon cancer, and other extraintestinal manifestations and cancers. Due to the relative rarity of the hamartomatous polyposis syndromes, recommendations for management are based on few studies. This U.S. Multi-Society Task Force on Colorectal Cancer consensus statement summarizes the clinical features, assesses the current literature, and provides guidance for diagnosis, assessment, and management of patients with the hamartomatous polyposis syndromes, with a focus on endoscopic management.

Diagnosis and Management of Cancer Risk in the Gastrointestinal Hamartomatous Polyposis Syndromes: Recommendations From the US Multi-Society Task Force on Colorectal Cancer.

The gastrointestinal hamartomatous polyposis syndromes are rare, autosomal dominant disorders associated with an increased risk of benign and malignant intestinal and extraintestinal tumors. They include Peutz-Jeghers syndrome, juvenile polyposis syndrome, the PTEN hamartoma tumor syndrome (including Cowden's syndrome and Bannayan-Riley-Ruvalcaba syndrome), and hereditary mixed polyposis syndrome. Diagnoses are based on clinical criteria and, in some cases, confirmed by demonstrating the presence of a germline pathogenic variant. The best understood hamartomatous polyposis syndrome is Peutz-Jeghers syndrome, caused by germline pathogenic variants in the STK11 gene. The management is focused on prevention of bleeding and mechanical obstruction of the small bowel by polyps and surveillance of organs at increased risk for cancer. Juvenile polyposis syndrome is caused by a germline pathogenic variant in either the SMAD4 or BMPR1A genes, with differing clinical courses. Patients with SMAD4 pathogenic variants may have massive gastric polyposis, which can result in gastrointestinal bleeding and/or protein-losing gastropathy. Patients with SMAD4 mutations usually have the simultaneous occurrence of hereditary hemorrhagic telangiectasia (juvenile polyposis syndrome-hereditary hemorrhagic telangiectasia overlap syndrome) that can result in epistaxis, gastrointestinal bleeding from mucocutaneous telangiectasias, and arteriovenous malformations. Germline pathogenic variants in the PTEN gene cause overlapping clinical phenotypes (known as the PTEN hamartoma tumor syndromes), including Cowden's syndrome and related disorders that are associated with an increased risk of gastrointestinal and colonic polyposis, colon cancer, and other extraintestinal manifestations and cancers. Due to the relative rarity of the hamartomatous polyposis syndromes, recommendations for management are based on few studies. This U.S Multi-Society Task Force on Colorectal Cancer consensus statement summarizes the clinical features, assesses the current literature, and provides guidance for diagnosis, assessment, and management of patients with the hamartomatous polyposis syndromes, with a focus on endoscopic management.

Review article: Lynch Syndrome-a mechanistic and clinical management update.

BACKGROUND: Lynch syndrome (LS) is an autosomal dominant familial condition caused by a pathogenic variant (PV) in a DNA mismatch repair gene, which then predisposes carriers to various cancers. AIM: To review the pathogenesis, clinical presentation, differential diagnosis and clinical strategies for detection and management of LS. METHODS: A narrative review synthesising knowledge from published literature, as well as current National Comprehensive Cancer Network guidelines for management of LS was conducted. RESULTS: LS tumours are characterised by unique pathogenesis, ultimately resulting in hypermutation, microsatellite instability and high immunogenicity that has significant implications for cancer risk, clinical presentation, treatment and surveillance. LS is one of the most common hereditary causes of cancer, and about 1 in 279 individuals carry a PV in an LS gene that predisposes to associated cancers. Individuals with LS have increased risks for colorectal, endometrial and other cancers, with significant variation in lifetime risk by LS-associated gene. CONCLUSIONS: As genetic testing becomes more widespread, the number of individuals identified with LS is expected to increase in the population. Understanding the pathogenesis of LS informs current strategies for detection and clinical management, and also guides future areas for clinical innovation. Unravelling the mechanisms by which these tumours evolve may help to more precisely tailor management by the gene involved.

The rising tide of early-onset colorectal cancer: a comprehensive review of epidemiology, clinical features, biology, risk factors, prevention, and early detection.

The incidence of early-onset colorectal cnacer-ie, colorectal cancer diagnosed in patients under the age of 50 years- has been increasing around the world. This Series paper provides a comprehensive review on the topic of early-onset colorectal cancer, including examining the epidemiology of early-onset colorectal cancer around the world, clinical and pathological features, genetic and epigenetic landscapes, and emerging data on the clinical risk factors associated with this malignancy. Evidence-based approaches to prevention and early detection are also presented.

Early-Age Onset Colorectal Neoplasia in Average-Risk Individuals Undergoing Screening Colonoscopy: A Systematic Review and Meta-Analysis.

BACKGROUND & AIMS: Incidence and mortality associated with early-age onset colorectal cancer (EAO-CRC) is increasing, prompting professional society recommendations to lower the screening age in average-risk individuals. The yield of screening individuals younger than 50 years is not known. METHODS: A systematic review of 3 databases from inception through July 2020 was performed in all languages that reported colonoscopy findings in average-risk individuals younger than 50 years. The primary outcomes were EAO colorectal neoplasia (CRN) and advanced colorectal neoplasia (aCRN) prevalence. Subgroup analyses were performed based on sex, geographic location, time period, and age, including comparison with those aged 50-59 years. Generalized linear mixed model with random intercept logistic regression and fixed subgroup effects were performed. RESULTS: Of 10,123 unique articles, 17 studies published between 2002 and 2020, including 51,811 average-risk individuals from 4 continents, were included. The pooled rate of EAO-CRN was 13.7% (95% confidence interval [CI], 0.112%-0.168%) and EAO-aCRN was 2.2% (95% CI, 0.016%-0.031%). Prevalence of CRC was 0.05% (95% CI, 0.00029%-0.0008%). Rates of EAO-CRN were higher in men compared with women (relative risk, 1.71%; 95% CI, 1.49%-1.98%), and highest in the United States (15.6%; 95% CI, 12.2%-19.7%) compared with Europe (14.9%; 95% CI, 6.9%-29.3%), East Asia (13.4%; 95% CI, 10.3%-17.2%), and the Middle East (9.8%; 95% CI, 7.8%-12.2%) (P = .04) The rate of EAO-CRN in age groups 45-49 years and 50-59 years was 17.8% (95% CI, 14.5%-21.6%) and 24.8% (95% CI, 19.5%-30.8%), respectively (P = .04). The rate of EAO-aCRN in age group 45-49 years was 3.6% (95% CI, 1.9%-6.7%) and 4.2% (95% CI, 3.2%-5.7%), respectively (P = .69). CONCLUSIONS: The rate of aCRN in individuals aged 45-49 years was similar to the rate observed in individual aged 50-59 years, suggesting that expanding screening to this population could yield a similar impact on colorectal cancer risk reduction.

Interval Colorectal Cancer 2006-2015: Novel Observations.

BACKGROUND: Screening for colorectal cancer (CRC) with colonoscopy has been credited for the majority of the decline in mortality over the past 40 years. However, colonoscopy is hampered by frequent interval cancers (ICs) occurring within 36 months after the last examination. Risk factors for IC imply that most misses are amenable to improved colonoscopic techniques. This study had two primary objectives: (1) to determine whether the proportion of persons with ICs has declined in association with improved approaches to the quality of colonoscopy and (2) to determine unrecognized causes for missed diagnoses. METHODS: This is a retrospective, single-center study of persons with CRC having been diagnosed within 6-36 months since the most recent colonoscopy between 2006 and 2015. Participants, ages 50 and 89 years, were evaluated specifically for technical features and findings of the most recent colonoscopy. RESULTS: Thirty-nine persons met the inclusion criteria for IC. Mean age was 69.3 years, range 50-86 years, women were 58%, races included 95% Caucasian, 2.5% Asian, and 2.5% African-American, and history of a first-degree relative with CRC was 26%. Symptoms led to the interval diagnosis in 83%, including iron-deficient anemia (38%), bleeding (25%), abdominal/pelvic pain (18%), and change in bowel habit (2.5%). Preexisting neoplasia was present in 72%. The CRC was located in the proximal colon in 51%. Late-stage disease was present in 45%. When compared to persons with an initial diagnosis of screen-detected late-onset CRC, differences were noted for older age, more women, more with a family history of CRC, and more with late-stage disease. The ratio of interval cancers to new cancers ranged between 6 and 11.5%. Findings indicating a "difficult examination" were observed in 14 cases (36%) compared to "easy or no difficulty" examinations in 25 (65%) cases. In a biennial analysis of IC rates between 2006 and 2015, the percentage of IC remained stable between 6 and 11.5%. CONCLUSIONS: ICs have been stable constituting 6-11.5% of all CRCs. A "difficult examination" was often associated with IC, may be a risk factor for this problem, and may be an important clue warranting further study.

Aspirin and the chemoprevention of cancers: A mathematical and evolutionary dynamics perspective.

Epidemiological data indicate that long-term low dose aspirin administration has a protective effect against the occurrence of colorectal cancer, both in sporadic and in hereditary forms of the disease. The mechanisms underlying this protective effect, however, are incompletely understood. The molecular events that lead to protection have been partly defined, but remain to be fully characterized. So far, however, approaches based on evolutionary dynamics have not been discussed much, but can potentially offer important insights. The aim of this review is to highlight this line of investigation and the results that have been obtained. A core observation in this respect is that aspirin has a direct negative impact on the growth dynamics of the cells, by influencing the kinetics of tumor cell division and death. We discuss the application of mathematical models to experimental data to quantify these parameter changes. We then describe further mathematical models that have been used to explore how these aspirin-mediated changes in kinetic parameters influence the probability of successful colony growth versus extinction, and how they affect the evolution of the tumor during aspirin administration. Finally, we discuss mathematical models that have been used to investigate the selective forces that can lead to the rise of mismatch-repair deficient cells in an inflammatory environment, and how this selection can be potentially altered through aspirin-mediated interventions. This article is categorized under: Models of Systems Properties and Processes > Mechanistic Models Analytical and Computational Methods > Analytical Methods Analytical and Computational Methods > Computational Methods.

Novel candidates in early-onset familial colorectal cancer.

In 20-30% of patients suspected of a familial colorectal cancer (CRC) syndrome, no underlying genetic cause is detected. Recent advances in whole exome sequencing have generated evidence for new CRC-susceptibility genes including POLE, POLD1 and NTHL1¸ but many patients remain unexplained. Whole exome sequencing was performed on DNA from nine patients from five different families with familial clusters of CRC in which traditional genetic testing failed to yield a diagnosis. Variants were filtered by minor allele frequencies, followed by prioritization based on in silico prediction tools, and the presence in cancer susceptibility genes or genes in cancer-associated pathways. Effects of frameshift variants on protein structure were modeled using I-Tasser. One known pathogenic variant in POLD1 was detected (p.S478N), together with variants in 17 candidate genes not previously associated with CRC. Additional in silico analysis using SIFT, PROVEAN and PolyPhen on the 14 missense variants indicated a possible damaging effect in nine of 14 variants. Modeling of the insertions/deletions showed a damaging effect of two variants in NOTCH2 and CYP1B1. One family was explained by a mutation in a known familial CRC gene. In the remaining four families, the most promising candidates found are a frameshift NOTCH2 and a missense RAB25 variant. This study provides potential novel candidate variants in unexplained familial CRC patients, however, functional validation is imperative to confirm the role of these variants in CRC tumorigenesis. Additionally, while whole exome sequencing enables detection of variants throughout the exome, other causes explaining the familial phenotype such as multiple single nucleotide polymorphisms accumulating to a polygenic risk or epigenetic events, might be missed with this approach.

Clinical and Genetic Characteristics of Colorectal Cancer in Persons under 50 Years of Age: A Review.

BACKGROUND: The incidence of colorectal cancer (CRC) in persons under the age of 50 years (EOCRC) is increasing even as the incidence of CRC in persons over age 50 is decreasing. This has led to recommendations to lower the age of CRC screening to age 45. It is not clear whether EOCRC is identical to CRCs in older patients or whether there are distinctive features between the two groups. AIMS AND METHODS: We reviewed the literature on the clinical and genetic aspects of EOCRC. RESULTS: We found that there is an increased likelihood of a strong genetic basis for EOCRC, but that at least 80% of cases do not come from the known high-penetrance cancer syndromes. Early-onset CRCs tend to occur in the distal colon or rectum, are more likely to be detected due to cancer-related symptoms, appear to be increasing in whites more than non-whites on a population-wide analysis, and are more likely to present in an advanced stage of disease. There are some unique genetic features of EOCRC, including an increased proportion of tumors with LINE-1 hypomethylation, and combined chromosomal and microsatellite stability. CONCLUSIONS: EOCRC deserves additional attention because of the high number of life years at risk with EOCRC, and the implications for earlier CRC screening. Additional focus is needed on determining whether some cases of EOCRC have a unique mechanistic basis.