结直肠锯齿状病变病理诊断及鉴别诊断

结直肠癌是最常见及致死率最高的癌症之一,其发生机制有两个主要通路:即经典的“腺瘤-腺癌”通路和锯齿状通路。锯齿状通路因其独特的分子病理学改变,而被认为是独立于经典的“腺瘤-腺癌”通路之外的结直肠癌发生路径。Longacre和Fenoglia Preiser于1990年对大肠“混合性增生性腺瘤样息肉”(mixed hyperplastic adenomatous polyps,MHAP)进行重新评估,并首次使用“锯齿状腺瘤”(serrated adenoma,SA)来定义此类病变。锯齿状病变的组织学分类及致癌的分子机制已部分阐明。然而,在实际工作中,病理医生,特别是年轻的病理医生对锯齿状病变分类及诊断仍存困惑。本文拟就锯齿状病变的分类、临床病理学特征、诊断及鉴别诊断要点进行讨论。     

Molecular heterogeneity of colorectal cancer: Implications for cancer control

Colorectal cancer (CRC) is a multi-pathway disease. A molecular approach to the classification of CRC utilises: (1) the type of genetic instability, specifically microsatellite instability (MSI) versus stable (MSS), and (2) the presence of DNA methylation or the CpG island methylator phenotype (CIMP). The MSS/CIMP-neg subset evolves through the classical adenoma-carcinoma sequence while the MSI/CIMP-pos and MSS/CIMP-pos subsets evolve through the recently recognised 'serrated pathway'. This review will show that the existence of two or more independent pathways to CRC is relevant to cancer prevention. In particular, new strategies for detecting and managing sessile serrated polyps will need to be developed and evaluated.     

The serrated neoplasia pathway of colorectal tumors: Identification of MUC5AC hypomethylation as an early marker of polyps with malignant potential

The serrated neoplasia pathway accounts for 20–30% of colorectal cancers (CRC), which are characterized by extensive methylation (CpG island methylation phenotype, CIMP), frequent BRAF mutation and high microsatellite instability (MSI). We recently identified MUC5AC mucin gene hypomethylation as a specific marker of MSI CRC. The early identification of preneoplastic lesions among serrated polyps is currently challenging. Here, we performed a detailed pathological and molecular analysis of a large series of colorectal serrated polyps and evaluated the usefulness of mucin genes MUC2 and MUC5AC to differentiate serrated polyps and to identify lesions with malignant potential. A series of 330 colorectal polyps including 218 serrated polyps [42 goblet cell‐rich hyperplastic polyps (GCHP), 68 microvesicular hyperplastic polyps (MVHP), 100 sessile serrated adenoma (SSA) and eight traditional serrated adenoma (TSA)] and 112 conventional adenomas was analyzed for BRAF/KRAS mutations, MSI, CIMP, MLH1 and MGMT methylation, and MUC2 and MUC5AC expression and methylation. We show that MUC5AC hypomethylation is an early event in the serrated neoplasia pathway, and specifically detects MVHP and SSA, arguing for a filiation between MVHP, SSA and CIMP‐H/MSI CRC, whereas GCHP and TSA arise from a distinct pathway. Moreover, MUC5AC hypomethylation specifically identified serrated lesions with BRAF mutation, CIMP‐H or MSI, suggesting that it may be useful to identify serrated neoplasia pathway‐related precursor lesions. Our data suggest that MVHP should be recognized among HP and require particular attention.     

Evolving molecular classification by genomic and proteomic biomarkers in colorectal cancer: potential implications for the surgical oncologist

Colorectal cancer (CRC) is one of the most frequent cancers in the Western world and represents a major health burden. CRC development is a multi-step process that spans 10-15years, thereby providing an opportunity for early detection and even prevention. As almost half of all patients undergoing surgery develop recurrent disease, surveillance is advocated, albeit with various means and intervals. Current screening and surveillance efforts have so far only had limited impact due to suboptimal compliance. Currently, CEA is the only biomarker in clinical use for CRC, but has suboptimal sensitivity and specificity. New and better biomarkers are therefore strongly needed. Non-invasive biomarkers may develop through the understanding of colorectal carcinogenesis. Three main pathways occur in CRC, including chromosomal instability (CIN), microsatellite instability (MSI) and epigenetic silencing through the CpG Island Methylator Phenotype (CIMP). These pathways have distinct clinical, pathological, and genetic characteristics, which can be used for molecular classification and comprehensive tumour profiling for improved diagnostics, prognosis and treatment in CRC. Molecular-biological research has advanced with the sequencing of the human genome and the availability of genomic and proteomic high-throughput technologies using different chip platforms, such as tissue microarrays, DNA microarrays, and mass spectrometry. This review aims to give an overview of the evolving biomarker concepts in CRC, with concerns on methods, and potential for clinical implications for the surgical oncologist.     

Serrated adenoma of the colorectum and the DNA-methylator phenotype

Serrated adenomas (SA) of the colorectum show features intermediate between hyperplastic polyps (HP) and adenomas. HP and SA are related lesions and there is now strong evidence for a 'serrated-polyp pathway' to colorectal cancer (CRC) that is largely independent of the classic adenoma-to-carcinoma sequence. A recently recognized lesion in this pathway is a HP variant characterized by relatively large size, atypical histology and proximal location in the colorectum. This HP variant has been given a variety of names in the literature including 'sessile SA' and 'type I SA'. Because this lesion lacks the traditional cytology of colorectal adenoma and in order to avoid confusion with SA, it is referred to in this review as sessile serrated polyp. SA are characterized by a heterogeneous group of changes at the molecular level, but a high proportion have BRAFmutations and DNA methylation. They may develop in HP or sessile serrated polyps, or may arise de novo. In the serratedpolyp pathway, the advent of genetic instability is likely to be an important rate-limiting step that drives rapid neoplastic evolution. Methylation and inactivation of the DNA repair genes MLH1 and MGMT (O-6-methylguanine-DNA methyltransferase) have been proposed as critical steps leading to genetic instability. Stretches of DNA rich in the bases guanine and cytosine (CpG islands; where p represents a phosphodiester bond linking adjacent cytosine and guanine bases) that are normally unmethylated may become methylated in malignant human colorectal tumors. Subsets of colorectal cancers with an unusually high number of methylated CpG islands have been described as having the 'CpG-island-methylator phenotype' It is possible that many, if not all, CRCs with the CpG-island-methylator phenotype evolve through the serrated-polyp pathway that would, therefore, explain approximately 20% of all CRCs. The current lack of guidelines for managing serrated polyps may explain the static incidence of proximal CRC, despite the falling incidence rates for left-sided CRC during the same time period.     

Serrated Pathway to Colorectal Carcinogenesis: A Molecular Perspective

Serrated polyps of the colorectum are formed by a spectrum of lesions that share a unique histological feature- the presence of sawtooth-shaped crypts. In the last decade, significant advances have been made on deciphering the molecular differences between these morphologically similar lesions, which has paved path for our current understanding for their neoplastic potential. In particular, the sessile serrated adenoma has become to be recognized as the precursor lesion for the group of sporadic colorectal cancers with high levels of microsatellite instability. These recent findings have challenged the long-held fundamental paradigm that all colon cancers arise via the classic adenoma-carcinoma sequence. Although it is welcome news that we now better understand the molecular pathogenesis of some proportion of sporadic cancers, nonetheless serrated polyps present with a major challenge for the early detection and management of colorectal cancer, which is no longer considered to be a homogenous entity.     

Development of invasive colon cancer with microsatellite instability in a patient with hyperplastic polyposis syndrome

The serrated pathway has recently been proposed as a route for the development of colorectal cancer with microsatellite instability. Hyperplastic polyposis syndrome is a rare syndrome defined by the presence of numerous serrated polyps, with a high risk of developing into colorectal cancer. We present here a case of hyperplastic polyposis syndrome developing into colorectal cancer with microsatellite instability from a serrated polyp. BRAF mutation and the loss of MLH1 protein were observed in the colorectal cancer, but not in the other serrated polyps around the colorectal cancer, suggesting that colorectal cancer with microsatellite instability develops rapidly from a specific serrated polyp with distinct molecular properties.     

Molecular Origins of Colon and Rectal Cancer: Not a Wnt–Wnt Situation

Extensive studies have provided crucial molecular and epidemiological insights into disease progression of late-onset colon cancer, the predominant colorectal cancer (CRC) subtype in the West. Most colon cancer cases are driven by mutational inactivation of the adenomatous polyposis coli tumor suppressor gene, causing chromosomal instability owing to constitutive activation of the Wnt pathway. A minor proportion of cases are caused by inactivation of the mismatch repair pathway resulting in microsatellite instability. Distinct etiological and molecular characteristics are, however, beginning to be unraveled in CRC occurring in developing nations. A preponderance of rectal (over colon) and early-onset (over late-onset) cancers appears to be the hallmark of CRC in developing countries. More importantly, the possible occurrence of unique non-Wnt tumorigenesis pathways in early-onset rectal cancer has been suggested in several populations. Although CRC research has mainly focused on the canonical Wnt signaling pathway for over two decades, it is imperative now to study alternative oncogenesis pathways to combat the ever-increasing rectal cancer burden in developing countries.     

Molecular patterns in the evolution of serrated lesion of the colorectum

Colorectal cancer (CRC) mostly develops from a variety of polyps following mainly three different molecular pathways: chromosomal instability (CIN), microsatellite instability (MSI) and CpG island methylation (CIMP). Polyps are classified histologically as conventional adenomas, hyperplastic polyps, sessile serrated adenomas/polyps (SSA/P) and traditional serrated adenomas (TSA). However, the association of these polyps with the different types of CRCs and the underlying genetic and epigenetic aberrations has yet to be resolved. In order to address this question we analyzed 140 tumors and 20 matched mucosae by array comparative genomic hybridization, by sequence analysis of the oncogenes BRAF, KRAS, PI3K3CA and by methylation arrays. MSI was tested indirectly by immunohistochemistry (IHC) and a loss of MLH1, MSH2, MSH6 or PMS2 was assigned as high microsatellite instability (MSI‐H), while low microsatellite instability (MSI‐L) was defined as MGMT IHC negativity only. CIN was detected in 78% of all MSI‐H CRCs, most commonly as a gain of chromosome 8. Methylation data analyses allowed classification of samples into four groups and detected similar methylation profiles in SSA/P and MSI‐H CRC. TSA also revealed aberrant methylation pattern, but clustered more heterogeneously and closer to microsatellite stable (MSS) CRCs. SSA/P, TSA and MSI‐H CRCs had the highest degree of promotor methylation (CIMP pathway). Chromosomal instability, in contrast to the established doctrine, is a common phenomenon in MSI CRCs, yet to a lower extent and at later stages than in MSS CRCs. Methylation analyses suggest that SSA/P are precursors for MSI‐H CRCs and follow the CIMP pathway.     

HNPCC and Sporadic MSI-H Colorectal Cancer: A Review of the Morphological Similarities and Differences

Morphological features may serve as diagnostically useful markers of colorectal cancer (CRC) with the microsatellite instability-high (MSI-H) phenotype. The most important of these are lymphocytic infiltration, mucin secretion and poor differentiation. These features are apparent in both sporadic MSI-H CRC and CRC occurring in the context of hereditary non-polyposis colorectal cancer (HNPCC). There is now strong evidence that that the two principal subtypes of MSI-H CRC evolve through different pathways. Sporadic MSI-H CRC orginate within serrated polyps with BRAF mutation and DNA methylation while CRC in HNPCC arise within conventional adenomas in which there is frequent mutation of APC or beta -catenin and/or K- ras. These early differences in pathogenesis translate into multiple morphological distinctions in the cancers developing through the two pathways. Lymphocytic infiltration, tumour budding (de-differentiation), and co-existing adenomas are more evident in HNPCC while mucin secretion, poor differentiation, tumour heterogeneity and glandular serration, and co-existing serrated polyps are more evident in sporadic MSI-H CRC. Sporadic MSI-H CRC are also characterized by cytoplasmic eosinophilia and nuclei that are large, round, vesicular and contain a prominent nucleolus while in HNPCC the cytological features recapitulate the basophilia and nuclear characteristics of conventional adenomas. In practice, lymphocytic infiltration is the most sensitive marker of MSI-H status in both sporadic CRC and HNPCC. The crucial distinction between HNPCC and sporadic MSI-H CRC should be achieved by means of all available data including family history, age at onset of malignancy and molecular features. There is increasing evidence that genetic factors may predispose to DNA methylation. This can result in familial clustering of MSI-H CRC in which the underlying mechanism is methylation of hMLH1 rather than germline mutation. Morphological features can assist is distinguishing such families from bona fide HNPCC families which they closely mimic.     

Exome sequencing characterizes the somatic mutation spectrum of early serrated lesions in a patient with serrated polyposis syndrome (SPS)

Background

Serrated or Hyperplastic Polyposis Syndrome (SPS, HPS) is a yet poorly defined colorectal cancer (CRC) predisposition characterised by the occurrence of multiple and/or large serrated polyps throughout the colon. A serrated polyp-CRC sequence (serrated pathway) of CRC formation has been postulated, however, to date only few molecular signatures of serrated neoplasia (BRAF, KRAS, RNF43 mutations, CpG Island Methylation, MSI) have been described in a subset of SPS patients and neither the etiology of the syndrome nor the distinct genetic alterations during tumorigenesis have been identified.

Methods

To identify somatic point mutations in potential novel candidate genes of SPS-associated lesions and the involved pathways we performed exome sequencing of eleven early serrated polyps obtained from a 41 year-old female patient with clinically confirmed SPS. For data filtering and analysis, standard pipelines were used. Somatic mutations were identified by comparison with leukocyte DNA and were validated by Sanger sequencing.

Results

The BRAF p.V600E or KRAS p.G12D mutation was identified in six polyps (~50%) and not found in polyps from the distal colon. In addition, we found seven unique rare somatic alterations of seven different genes in four serrated tumours, all of which are missense variants. The variant in ABI3BP and CATSPERB are predicted to be deleterious. No established cancer gene or candidate genes related to serrated tumorigenesis were affected.

Conclusions

Somatic mutations seem to be rare events in early hyperplastic and serrated lesions of SPS patients. Neither frequently affected genes nor enrichment of specific pathways were observed. Thus, other alterations such as non-coding variants or epigenetic changes might be the major driving force of tumour progression in SPS.

     

Serrated carcinomas form a subclass of colorectal cancer with distinct molecular basis

Serrated colorectal carcinomas (CRCs) are morphologically different from conventional CRCs and have been proposed to follow a distinct pathway of CRC formation. Despite studies of single molecular events in this tumor type, the diagnosis of serrated CRC relies on morphology and the putative unique biological character of these tumors has not been established. Here we show that the gene expression profiling of 37 CRCs separated serrated and conventional CRCs into two distinct branches in unsupervised hierarchical clustering (P-value 7.8 x 10(-7)), and revealed 201 differentially expressed genes representing potential biomarkers for serrated CRC. Immunohistochemistry was utilized to verify the key findings in the 37 CRCs examined by expression profiling, and a separate validation set of 37 serrated and 86 conventional CRCs was examined to evaluate the candidate biomarkers in an extended sample material. Ephrin receptor B2, hypoxia-inducible factor 1-alpha and patched appeared as proteins important for genesis of serrated CRC. This study establishes serrated CRCs as a biologically distinct subclass of CRC and represents a step forward in the molecular classification of these cancers. The study also provides a platform to understand the molecular basis of serrated CRC and in long term may contribute to the development of specific treatment options for this tumor type.     

Colorectal cancer: a researcher’s perspective of the molecular angel’s gone eccentric in the Vale of Kashmir

Colorectal cancer (CRC), being the most common cancer, is the major cause of mortality and morbidity worldwide. In Kashmir, CRC has been found to be the third most common gastrointestinal cancer after esophageal and gastric. The etiology of CRC involves two pathways: chromosomal instability (CIN) and microsatellite instability. CIN occurs in 80–85 % of CRC resulting in either gross changes in chromosome structure and number or point mutations in the chromosomes. Many molecular studies have been carried out on CRC in Kashmir so as to elucidate the role of tumor suppressor genes and oncogenes in modulating the carcinogenesis. We searched the various literature databases including Medline, PubMed, ASCO abstracts, and ESMO abstracts for the papers regarding colorectal cancer published in English using the terms “Kashmir,” “colorectal cancer,” “colon cancer,” “rectal cancer,” “carcinogenesis,” “epidemiology,” “genetics,” “mutation,” and “polymorphism.” Here in this review, I have shed light on the different studies carried on CRC in our Kashmiri population in an attempt to share what we know so far about the molecular carcinogenesis of CRC in Kashmir.     

Age-Specific Differences in the Risk of Colorectal Precursor Lesions Among Patients with Type 2 Diabetes Undergoing Surveillance Colonoscopy

Background: The incidence rate of colorectal cancer (CRC) in young adults is rising in parallel with type 2 diabetes (T2D). The majority of CRC develop through two main subtypes of precursor lesions; adenomas and serrated lesions. The associations between age and T2D on development of precursor lesions remain uncertain. Objectives: We studied the association of T2D with the development of adenomas and serrated lesions in individuals <50 versus ≥50 years of age, in a population undergoing long-term regular surveillance colonoscopy due to an elevated risk of CRC. Methods: A case-control study was conducted on patients who were enrolled in a surveillance colonoscopy program between 2010-2020. Findings at colonoscopy, clinical and demographic features were collected. Adjusted and unadjusted binary logistic regression assessed the association of age, T2D, sex, and other medical conditions and lifestyle-related factors with different subtypes of precursor lesions diagnosed at colonoscopy. Cox proportional hazards model analysis determined the association of T2D and other confounders with development time for precursor lesions. Results: Cases included 412 patients <50y [mean age 38.7 (range, 24-49y)] and 824 sex-matched controls ≥50y [62.1 (50-75y)]. Individuals <50y were less likely to have been diagnosed with T2D than those ≥50y (7% vs 22%, P-value<0.001). During the follow-up period, there was no significant association between T2D and diagnosis of any precursor lesions, but when considering development time, individuals with T2D developed non-significant adenomas earlier than those without T2D (HR =1.46; 95% CI: 1.14–1.87; P-value=0.003). However, this was not independent of age or findings at index colonoscopy. Conclusions: T2D does not further increase the incidence of adenomas or serrated lesions in either a young or older cohort undergoing long-term surveillance colonoscopy.     

Molecular therapy of colorectal cancer: Progress and future directions

Colorectal cancer (CRC) remains one of the most common types of cancer and leading causes of cancer death worldwide. Although the introduction of cytotoxic drugs such as oxaliplatin, irinotecan and fluorouracil has improved the treatment of advanced CRC, the individual response to chemoradiotherapy varies tremendously from one patient to another. However, recent progress in CRC molecular therapies may provide new insight into the treatment of this disease. Currently, components of the EGFR, VEGF, Wnt and NF‐kB pathways are the most important targets for CRC therapy. This review chronicles the development of molecular CRC therapies over the past few decades. We also provide an update on the current progress of research concerning the molecular pathways leading to CRC and discuss the possible implications for CRC therapy.     

Focus on genetic and epigenetic events of colorectal cancer pathogenesis: implications for molecular diagnosis

Originally, colorectal cancer (CRC) tumorigenesis was understood as a multistep process that involved accumulation of tumor suppressor genes and oncogenes mutations, such as APC, TP53 and KRAS. However, this assumption proposed a relatively limited repertoire of genetic alterations. In the last decade, there have been major advances in knowledge of multiple molecular pathways involved in CRC pathogenesis, particularly regarding cytogenetic and epigenetic events. Microsatellite instability, chromosomal instability and CpG island methylator phenotype are the most analyzed cytogenetic changes, while DNA methylation, modifications in histone proteins and microRNAs (miRNAs) were analyzed in the field of epigenetic alterations. Therefore, CRC development results from interactions at many levels between genetic and epigenetic amendments. Furthermore, hereditary cancer syndrome and individual or environmental risk factors should not be ignored. The difficulties in this setting are addressed to understand the molecular basis of individual susceptibility to CRC and to determine the roles of genetic and epigenetic alterations, in order to yield more effective prevention strategies in CRC patients and directing their treatment. This review summarizes the most investigated biomolecular pathways involved in CRC pathogenesis, their role as biomarkers for early CRC diagnosis and their possible use to stratify susceptible patients into appropriate screening or surveillance programs.     

Microsatellite instability in aberrant crypt foci from patients without concurrent colon cancer

Aberrant crypt foci (ACF) are microscopic surface abnormalities that are putative precursors to colorectal cancer (CRC). ACF exhibit similar histological and molecular abnormalities to adenomas and CRC and potentially represent useful biomarkers of cancer risk. Microsatellite instability (MSI) is one molecular abnormality identified in concurrent ACF from CRC patients that may indicate a risk for progression. To determine if MSI can be detected in ACF from cancer-free subjects, we examined 45 ACF from 20 subjects undergoing colonoscopies. The group included 12 patients at elevated risk for CRC based on family history of CRC or personal history of CRC or advanced adenoma and 8 patients with no known risk factors. ACF were identified using close-focus magnifying chromendoscopy and collected by biopsy in situ. Genomic DNA was prepared from ACF and adjacent normal colonic epithelium isolated by laser capture microdissection and analyzed for MSI. MSI was identified in at least one marker from 9 of 30 (30%) lesions from patients at elevated risk for CRC and in 2 of 15 (13%) lesions from average risk patients. Using methylation-specific PCR analysis, we also examined the ACF for promoter hypermethylation of the DNA repair genes hMLH1 and MGMT and found moderate changes (8/39 and 3/32, respectively). Although we found only a limited relationship between hMLH1 hypermethylation and MSI, all the lesions with MGMT hypermethylation displayed an MSI-low phenotype. These lesions may be precursors to MSI-low CRC, providing a potential early biomarker to assess the effects of cancer prevention strategies.