The incidence of early-onset colorectal cancer (CRC), which occurs in individuals <50 years of age, has been increasing worldwide and particularly in high-income countries. The reasons for this ...increase remain unknown but plausible hypotheses include greater exposure to potential risk factors, such as a Western-style diet, obesity, physical inactivity and antibiotic use, especially during the early prenatal to adolescent periods of life. These exposures can not only cause genetic and epigenetic alterations in colorectal epithelial cells but also affect the gut microbiota and host immunity. Early-onset CRCs have differential clinical, pathological and molecular features compared with later-onset CRCs. Certain existing resources can be utilized to elucidate the aetiology of early-onset CRC and inform the development of effective prevention, early detection and therapeutic strategies; however, additional life-course cohort studies spanning childhood and young adulthood, integrated with prospective biospecimen collections, omics biomarker analyses and a molecular pathological epidemiology approach, are needed to better understand and manage this disease entity. In this Perspective, we summarize our current understanding of early-onset CRC and discuss how we should strategize future research to improve its prevention and clinical management.
Among 88,902 participants followed over a period of 22 years in the Nurses' Health Study and the Health Professionals Follow-up Study, colon cancer mortality was reduced after screening sigmoidoscopy ...(hazard ratio, 0.59) and screening colonoscopy (hazard ratio, 0.32).
Randomized, controlled trials have shown that screening with flexible sigmoidoscopy reduces the incidence of colorectal cancer and associated mortality, albeit with diminished effectiveness for cancers of the proximal colon.
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Although comparable data from randomized, controlled trials of screening colonoscopy are not yet available,
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colonoscopy is also widely endorsed by expert bodies for population-based screening, largely on the basis of case–control studies that show associations with reduced colorectal-cancer incidence and mortality.
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However, as with flexible sigmoidoscopy, there is uncertainty about the effectiveness of colonoscopy in reducing the incidence of and mortality associated with proximal colon cancer
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Molecular pathological epidemiology (MPE) is an integrative field that utilizes molecular pathology to incorporate interpersonal heterogeneity of a disease process into epidemiology. In each ...individual, the development and progression of a disease are determined by a unique combination of exogenous and endogenous factors, resulting in different molecular and pathological subtypes of the disease. Based on “the unique disease principle,” the primary aim of MPE is to uncover an interactive relationship between a specific environmental exposure and disease subtypes in determining disease incidence and mortality. This MPE approach can provide etiologic and pathogenic insights, potentially contributing to precision medicine for personalized prevention and treatment. Although breast, prostate, lung, and colorectal cancers have been among the most commonly studied diseases, the MPE approach can be used to study any disease. In addition to molecular features, host immune status and microbiome profile likely affect a disease process, and thus serve as informative biomarkers. As such, further integration of several disciplines into MPE has been achieved (e.g., pharmaco-MPE, immuno-MPE, and microbial MPE), to provide novel insights into underlying etiologic mechanisms. With the advent of high-throughput sequencing technologies, available genomic and epigenomic data have expanded dramatically. The MPE approach can also provide a specific risk estimate for each disease subgroup, thereby enhancing the impact of genome-wide association studies on public health. In this article, we present recent progress of MPE, and discuss the importance of accounting for the disease heterogeneity in the era of big-data health science and precision medicine.
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.
Metagenomic studies using next-generation sequencing technologies have revealed rich human intestinal microbiome, which likely influence host immunity and health conditions including cancer. Evidence ...indicates a biological link between altered microbiome and cancers in the digestive system.
Escherichia coli
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Bacteroides fragilis
have been found to be enriched in colorectal mucosal tissues from patients with familial adenomatous polyposis that is caused by germline
APC
mutations. In addition, recent studies have found enrichment of certain oral bacteria, viruses, and fungi in tumor tissue and fecal specimens from patients with gastrointestinal cancer. An integrative approach is required to elucidate the role of microorganisms in the pathogenic process of gastrointestinal cancers, which develop through the accumulation of somatic genetic and epigenetic alterations in neoplastic cells, influenced by host genetic variations, immunity, microbiome, and environmental exposures. The transdisciplinary field of molecular pathological epidemiology (MPE) offers research frameworks to link germline genetics and environmental factors (including diet, lifestyle, and pharmacological factors) to pathologic phenotypes. The integration of microbiology into the MPE model (microbiology–MPE) can contribute to better understanding of the interactive role of environment, tumor cells, immune cells, and microbiome in various diseases. We review major clinical and experimental studies on the microbiome, and describe emerging evidence from the microbiology–MPE research in gastrointestinal cancers. Together with basic experimental research, this new research paradigm can help us to develop new prevention and treatment strategies for gastrointestinal cancers through targeting of the microbiome.
Serrated polyps (SPs) and conventional adenomas are precursor lesions for colorectal cancer (CRC), but they are believed to arise via distinct pathways. We characterized risk factor profiles for SPs ...and conventional adenomas in a post hoc analysis of data from 3 large prospective studies.
We collected data from the Nurses’ Health Study, the Nurses’ Health Study 2, and the Health Professionals Follow-up Study on subjects who developed SPs or conventional adenomas. Our analysis comprised 141,143 participants who had undergone lower gastrointestinal endoscopy, provided updated diet and lifestyle data every 2–4 years, and were followed until diagnosis of a first polyp. We assessed 13 risk factors for CRC in patients with SPs or conventional adenomas and examined the associations according to histopathology features.
We documented 7945 SPs, 9212 conventional adenomas, and 2382 synchronous SPs and conventional adenomas during 18–20 years of follow-up. Smoking, body mass index, alcohol intake, family history of CRC, and height were associated with higher risk of SPs and conventional adenomas, whereas higher intake of vitamin D and marine omega-3 fatty acid were associated with lower risk. The associations tended to be stronger for synchronous SPs and conventional adenomas. Smoking, body mass index, and alcohol intake were more strongly associated with SPs than conventional adenomas (P for heterogeneity <.05), whereas physical activity and intake of total folate and calcium were inversely associated with conventional adenomas but not SPs. For SPs and conventional adenomas, the associations tended to be stronger for polyps in the distal colon and rectum, of 10 mm or larger or with advanced histology.
In an analysis of data from 3 large prospective studies, we found that although SPs and conventional adenomas share many risk factors, some factors are more strongly associated with one type of lesion than the other. These findings provide support for the etiologic heterogeneity of colorectal neoplasia.
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Endoscopic screening reduces incidence and mortality of colorectal cancer (CRC) because precursor lesions, such as conventional adenomas or serrated polyps, are removed. Individuals with ...polypectomies are advised to undergo colonoscopy surveillance to prevent CRC. However, guidelines for surveillance intervals after diagnosis of a precursor lesion, particularly for individuals with serrated polyps, vary widely, and lack sufficient supporting evidence. Consequently, some high-risk patients do not receive enough surveillance and lower-risk subjects receive excessive surveillance.
We examined the association between findings from first endoscopy and CRC risk among 122,899 participants who underwent flexible sigmoidoscopy or colonoscopy in the Nurses’ Health Study 1 (1990–2012), Nurses’ Health Study 2 (1989–2013), or the Health Professionals Follow-up Study (1990–2012). Endoscopic findings were categorized as no polyp, conventional adenoma, or serrated polyp (hyperplastic polyp, traditional serrated adenoma, or sessile serrated adenoma, with or without cytological dysplasia). Conventional adenomas were classified as advanced (≥10 mm, high-grade dysplasia, or tubulovillous or villous histology) or nonadvanced, and serrated polyps were assigned to categories of large (≥10 mm) or small (<10 mm). We used a Cox proportional hazards regression model to calculate the hazard ratios (HRs) of CRC incidence, after adjusting for various potential risk factors.
After a median follow-up period of 10 years, we documented 491 incident cases of CRC: 51 occurred in 6161 participants with conventional adenomas, 24 in 5918 participants with serrated polyps, and 427 in 112,107 participants with no polyp. Compared with participants with no polyp detected during initial endoscopy, the multivariable HR for incident CRC in individuals with an advanced adenoma was 4.07 (95% confidence interval CI 2.89–5.72) and the HR for CRC in individuals with a large serrated polyp was 3.35 (95% CI 1.37–8.15). In contrast, there was no significant increase in risk of CRC in patients with nonadvanced adenomas (HR 1.21; 95% CI 0.68–2.16, P = .52) or small serrated polyps (HR 1.25; 95% CI 0.76–2.08; P = .38).
These findings provide support for guidelines that recommend repeat lower endoscopy within 3 years of a diagnosis of advanced adenoma and large serrated polyps. In contrast, patients with nonadvanced adenoma or small serrated polyps may not require more intensive surveillance than patients without polyps.
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Toll-like receptors(TLRs)are germ line encoded innate immune sensors that recognize conserved microbial structures and host alarmins,and signal expression of major histocompatibility complex ...proteins,costimulatory molecules,and inflammatory mediators by macrophages,neutrophils,dendritic cells,and other cell types.These protein receptors are characterized by their ability to respond to invading pathogens promptlyby recognizing particular TLR ligands,including flagellin and lipopolysaccharide of bacteria,nucleic acids derived from viruses,and zymosan of fungi.There are2 major TLR pathways;one is mediated by myeloid differentiation factor 88(MYD88)adaptor proteins,and the other is independent of MYD88.The MYD88-dependent pathway involves early-phase activation of nuclear factor of kappa light polypeptide gene enhancer in B-cells 1(NF-κB1)and all the TLRs,except TLR3,have been shown to activate this pathway.TLR3and TLR4 act via MYD88-independent pathways with delayed activation of NF-κB signaling.TLRs play a vital role in activating immune responses.TLRs have been shown to mediate inflammatory responses and maintain epithelial barrier homeostasis,and are highly likely to be involved in the activation of a number of pathways following cancer therapy.Colorectal cancer(CRC)is one of the most common cancers,and accounts for almost half a million deaths annually worldwide.Inflammation is considered a risk factor for many common malignancies including cancers of the colorectum.The key molecules involved in inflammation-driven carcinogenesis include TLRs.As sensors of cell death and tissue remodeling,TLRs may have a universal role in cancer;stimulation of TLRs to activate the innate immune system has been a legitimate therapeutic strategy for some years.TLRs 3/4/7/8/9 are all validated targets for cancer therapy,and a number of companies are developing agonists and vaccine adjuvants.On the other hand,antagonists may favor inhibition of signaling responsible for autoimmune responses.In this paper,we review TLR signaling in CRC from carcinogenesis to cancer therapy.
Colorectal cancers comprise a complex mixture of malignant cells, nontransformed cells, and microorganisms. Fusobacterium nucleatum is among the most prevalent bacterial species in colorectal cancer ...tissues. Here we show that colonization of human colorectal cancers with Fusobacterium and its associated microbiome—including Bacteroides, Selenomonas, and Prevotella species—is maintained in distal metastases, demonstrating microbiome stability between paired primary and metastatic tumors. In situ hybridization analysis revealed that Fusobacterium is predominantly associated with cancer cells in the metastatic lesions. Mouse xenografts of human primary colorectal adenocarcinomas were found to retain viable Fusobacterium and its associated microbiome through successive passages. Treatment of mice bearing a colon cancer xenograft with the antibiotic metronidazole reduced Fusobacterium load, cancer cell proliferation, and overall tumor growth. These observations argue for further investigation of antimicrobial interventions as a potential treatment for patients with Fusobacterium-associated colorectal cancer.
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