Loss of expression of the SWI/SNF chromatin remodeling subunit BRG1/SMARCA4 is frequently observed in intraductal papillary mucinous neoplasms of the pancreas

SWI/SNF Complex-Deficient Undifferentiated Carcinoma of the Pancreas: Clinicopathologic and Genomic Analysis

Inactivating alterations in the SWItch/Sucrose NonFermentable (SWI/SNF) Chromatin Remodeling Complex subunits have been described in multiple tumor types. Recent studies focused on SMARC subunits of this complex to understand their relationship with tumor characteristics and therapeutic opportunities. To date, pancreatic cancer with these alterations has not been well studied, although isolated cases of undifferentiated carcinomas have been reported. Herein, we screened 59 pancreatic undifferentiated carcinomas for alterations in SWI/SNF complex-related (SMARCB1 [BAF47/INI1], SMARCA4 [BRG1], SMARCA2 [BRM]) proteins and/or genes using immunohistochemistry and/or next-generation sequencing. Cases with alterations in SWI/SNF complex-related proteins/genes were compared with cases without alterations, as well as with 96 conventional pancreatic ductal adenocarcinomas (PDAC). In all tumor groups, mismatch repair and PD-L1 protein expression were also evaluated. Thirty of 59 (51%) undifferentiated carcinomas had a loss of SWI/SNF complex-related protein expression or gene alteration. Twenty-seven of 30 (90%) SWI-/SNF-deficient undifferentiated carcinomas had rhabdoid morphology (vs 9/29 [31%] SWI-/SNF-retained undifferentiated carcinomas; P < .001) and all expressed cytokeratin, at least focally. Immunohistochemically, SMARCB1 protein expression was absent in 16/30 (53%) cases, SMARCA2 in 4/30 (13%), and SMARCA4 in 4/30 (13%); both SMARCB1 and SMARCA2 protein expressions were absent in 1/30 (3%). Five of 8 (62.5%) SWI-/SNF-deficient undifferentiated carcinomas that displayed loss of SMARCB1 protein expression by immunohistochemistry were found to have corresponding SMARCB1 deletions by next-generation sequencing. Analysis of canonical driver mutations for PDAC in these cases showed KRAS (2/5) and TP53 (2/5) abnormalities. Median combined positive score for PD-L1 (E1L3N) was significantly higher in the undifferentiated carcinomas with/without SWI/SNF deficiency compared with the conventional PDACs (P < .001). SWI-/SNF-deficient undifferentiated carcinomas were larger (P < .001) and occurred in younger patients (P < .001). Patients with SWI-/SNF-deficient undifferentiated carcinoma had worse overall survival compared with patients with SWI-/SNF-retained undifferentiated carcinoma (P = .004) and PDAC (P < .001). Our findings demonstrate that SWI-/SNF-deficient pancreatic undifferentiated carcinomas are frequently characterized by rhabdoid morphology, exhibit highly aggressive behavior, and have a negative prognostic impact. The ones with SMARCB1 deletions appear to be frequently KRAS wild type. Innovative developmental therapeutic strategies targeting this genomic basis of the SWI/SNF complex and the therapeutic implications of EZH2 inhibition (NCT03213665), SMARCA2 degrader (NCT05639751), or immunotherapy are currently under investigation.

Lobular Endocervical Glandular Hyperplasia, a mimicker and potential pitfall for HPV-independent well differentiated Gastric-type Endocervical Adenocarcinoma: Case report and literature review focusing on histology, immunophenotype, and molecular findings

Lobular glandular endocervical hyperplasia is an uncommon benign entity within the spectrum of gastric-type endocervical lesions. We report a case of a 48-year-old woman who presented with a palpable mass and watery vaginal discharge. Ultrasound revealed an 8 cm × 4 cm × 3 cm multicystic mass affecting the cervix, and hysterectomy was performed. The well-delimited multicystic, mucinous mass distorted the entire cervix. Microscopically, endocervical glandular proliferation with a lobular architecture was observed. The glands were lined with a single layer of tall, mucin-rich, columnar cells with basal and bland nuclei. The lesion was positive for MUC6 marker and hormonal receptors were negative, while P53 expression was normal. Three years later, the patient remained disease free. Here, we discuss the differential diagnosis between lobular glandular endocervical hyperplasia and similar conditions, particularly gastric-type endocervical adenocarcinoma, and review the literature focusing on the molecular pathways underlying gastric-type endocervical lesions. This case highlights the importance of accurate diagnosis to ensure favorable outcomes.

(mis)-Targeting of SWI/SNF complex(es) in cancer

The ATP-dependent chromatin remodeling complex SWI/SNF (also called BAF) is critical for the regulation of gene expression. During the evolution from yeast to mammals, the BAF complex has evolved an enormous complexity that contains a high number of subunits encoded by various genes. Emerging studies highlight the frequent involvement of altered mammalian SWI/SNF chromatin-remodeling complexes in human cancers. Here, we discuss the recent advances in determining the structure of SWI/SNF complexes, highlight the mechanisms by which mutations affecting these complexes promote cancer, and describe the promising emerging opportunities for targeted therapies.

Clinical and Molecular Attributes and Evaluation of Pancreatic Cystic Neoplasm

Intraductal papillary mucinous neoplasms (IPMNs) and mucinous cystic neoplasms (MCNs) are all considered "Pancreatic cystic neoplasms (PCNs)" and show a varying risk of developing into pancreatic ductal adenocarcinoma (PDAC). These lesions display different molecular characteristics, mutations, and clinical manifestations. A lack of detailed understanding of PCN subtype characteristics and their molecular mechanisms limits the development of efficient diagnostic tools and therapeutic strategies for these lesions. Proper in vivo mouse models that mimic human PCNs are also needed to study the molecular mechanisms and for therapeutic testing. A comprehensive understanding of the current status of PCN biology, mechanisms, current diagnostic methods, and therapies will help in the early detection and proper management of patients with these lesions and PDAC. This review aims to describe all these aspects of PCNs, specifically IPMNs, by describing the future perspectives.

Genetic Mutations of Pancreatic Cancer and Genetically Engineered Mouse Models

Simple Summary

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy. Recent multi-gene analysis approaches such as next-generation sequencing have provided useful information on the molecular characterization of pancreatic tumors. Different types of pancreatic cancer and precursor lesions are characterized by specific molecular alterations. Genetically engineered mouse models (GEMMs) of PDAC are useful tools to understand the roles of altered genes. Most GEMMs are driven by oncogenic Kras, and can recapitulate the histological and molecular hallmarks of human PDAC and comparable precursor lesions. In this review, we summarize the main molecular alterations found in pancreatic neoplasms and GEMMs developed based on these alterations.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy, and the seventh leading cause of cancer-related deaths worldwide. An improved understanding of tumor biology and novel therapeutic discoveries are needed to improve overall survival. Recent multi-gene analysis approaches such as next-generation sequencing have provided useful information on the molecular characterization of pancreatic tumors. Different types of pancreatic cancer and precursor lesions are characterized by specific molecular alterations. Genetically engineered mouse models (GEMMs) of PDAC are useful to understand the roles of altered genes. Most GEMMs are driven by oncogenic Kras, and can recapitulate the histological and molecular hallmarks of human PDAC and comparable precursor lesions. Advanced GEMMs permit the temporally and spatially controlled manipulation of multiple target genes using a dual-recombinase system or CRISPR/Cas9 gene editing. GEMMs that express fluorescent proteins allow cell lineage tracing to follow tumor growth and metastasis to understand the contribution of different cell types in cancer progression. GEMMs are widely used for therapeutic optimization. In this review, we summarize the main molecular alterations found in pancreatic neoplasms, developed GEMMs, and the contribution of GEMMs to the current understanding of PDAC pathobiology. Furthermore, we attempted to modify the categorization of altered driver genes according to the most updated findings.

Intraductal Papillary Mucinous Neoplasms of the Pancreas: A Review of Their Genetic Characteristics and Mouse Models

Simple Summary

Pancreatic cancer is one of the deadliest cancers with the lowest survival rate. Little progress has been achieved in prolonging the survival for patients with pancreatic adenocarcinoma. Hence, special attention should be paid to pre-cancerous lesions, for instance, an intraductal papillary mucinous neoplasm (IPMN). Here, we reviewed its genetic characteristics and the mouse models involving mutations in specific pathways, and updated our current perception of how this lesion develops into a precursor of invasive cancer.

Abstract

The intraductal papillary mucinous neoplasm (IPMN) is attracting research attention because of its increasing incidence and proven potential to progress into invasive pancreatic ductal adenocarcinoma (PDAC). In this review, we summarized the key signaling pathways or protein complexes (GPCR, TGF, SWI/SNF, WNT, and PI3K) that appear to be involved in IPMN pathogenesis. In addition, we collected information regarding all the genetic mouse models that mimic the human IPMN phenotype with specific immunohistochemistry techniques. The mouse models enable us to gain insight into the complex mechanism of the origin of IPMN, revealing that it can be developed from both acinar cells and duct cells according to different models. Furthermore, recent genomic studies describe the potential mechanism by which heterogeneous IPMN gives rise to malignant carcinoma through sequential, branch-off, or de novo approaches. The most intractable problem is that the risk of malignancy persists to some extent even if the primary IPMN is excised with a perfect margin, calling for the re-evaluation and improvement of diagnostic, pre-emptive, and therapeutic measures.

The role of the SWI/SNF chromatin remodeling complex in pancreatic ductal adenocarcinoma

ATP-dependent chromatin remodeling complexes are a group of epigenetic regulators that can alter the assembly of nucleosomes and regulate the accessibility of transcription factors to DNA in order to modulate gene expression. One of these complexes, the SWI/SNF chromatin remodeling complex is mutated in more than 20% of human cancers. We have investigated the roles of the SWI/SNF complex in pancreatic ductal adenocarcinoma (PDA), which is the most lethal type of cancer. Here, we reviewed the recent literature regarding the role of the SWI/SNF complex in pancreatic tumorigenesis and current knowledge about therapeutic strategies targeting the SWI/SNF complex in PDA. The subunits of the SWI/SNF complex are mutated in 14% of human PDA. Recent studies have shown that they have context-dependent oncogenic or tumor-suppressive roles in pancreatic carcinogenesis. To target its tumor-suppressive properties, synthetic lethal strategies have recently been developed. In addition, their oncogenic properties could be novel therapeutic targets. The SWI/SNF subunits are potential therapeutic targets for PDA, and further understanding of the precise role of the SWI/SNF complex subunits in PDA is required for further development of novel strategies targeting SWI/SNF subunits against PDA.

SWI/SNF-deficient cancers of the Gastroenteropancreatic tract: an in-depth review of the literature and pathology

The SWItch Sucrose non-fermentable (SWI/SNF) complex is a large, multi-subunit ATP-dependent nucleosome remodeling complex that acts as a tumor suppressor by modulating transcription. Mutations of SWI/SNF subunits have been described in relation to developmental disorders, hereditary SWI/SNF deficiency syndromes, as well as malignancies. In this review we summarize the current literature in regards to SWI/SNF-deficient tumors of the luminal gastrointestinal tract (GIT) and pancreas. As a group they range from moderately to undifferentiated tumors composed of monotonous anaplastic cells, prominent macronucleoli and a variable rhabdoid cell component. Deficiency of a SWI/SNF subunit is typified by complete loss of nuclear staining by immunohistochemistry for respective subunit.

The clinicopathological and molecular analysis of gastric cancer with altered SMARCA4 expression

AIMS

In this study, we examine the clinicopathological and molecular features of gastric cancer (GC) with SMARCA4 alterations.

METHODS AND RESULTS

We screened SMARCA4 alterations using immunohistochemistry on 1199 surgically resected GCs with information on Epstein-Barr virus (EBV), microsatellite instability (MSI) and other SWI/SNF subunits. SMARCA4, SMARCA2 and ARID1A mutations were investigated by targeted sequencing. The clinicopathological significance was determined by statistical analysis. Twenty-seven cases (2%) with altered SMARCA4 expression were identified, exhibiting completely lost (six), reduced (nine) or heterogeneous (12) patterns. Frequent concomitant alterations of other SWI/SNF subunits were noted with an unusual discordant spatial heterogeneity. In comparison with SMARCA4-retained GCs, SMARCA4-lost GCs were observed more frequently in the non-EBV/MSI subgroup (five of six) and reduced or heterogeneous SMARCA4 expression mainly occurred in EBV- or MSI-associated cases (six of nine and six of 12, respectively; P < 0.001). Histologically, SMARCA4-altered GC, irrespective of expression pattern, demonstrated divergent histomorphology, spanning tubular, poorly cohesive or mixed, neuroendocrine to solid and undifferentiated carcinoma, with a predilection to the latter two (P < 0.001). De-differentiation-like transition and rhabdoid features were noted in a minority of cases. For overall survival, altered SMARCA4 expression was an unfavourable prognostic factor in stage III, EBV-associated GC and non-EBV/MSI intestinal subtype (P ≤ 0.001). SMARCA4 or ARID1A mutations were detected mainly in SMARCA4-lost or reduced GC, respectively.

CONCLUSIONS

SMARCA4-altered GCs are rare and have intratumoral heterogeneity, histomorphological diversity, conditional prognostic significance and various genetic drivers. SMARCA4-lost GC may represent a genuine SMARCA4-deficient neoplasm, but most SMARCA4-reduced/heterogeneous cases are secondary to ARID1A collapse or associated with different genotypes.

The SWI/SNF complex in cancer - biology, biomarkers and therapy

Cancer genome-sequencing studies have revealed a remarkably high prevalence of mutations in genes encoding subunits of the SWI/SNF chromatin-remodelling complexes, with nearly 25% of all cancers harbouring aberrations in one or more of these genes. A role for such aberrations in tumorigenesis is evidenced by cancer predisposition in both carriers of germline loss-of-function mutations and genetically engineered mouse models with inactivation of any of several SWI/SNF subunits. Whereas many of the most frequently mutated oncogenes and tumour-suppressor genes have been studied for several decades, the cancer-promoting role of mutations in SWI/SNF genes has been recognized only more recently, and thus comparatively less is known about these alterations. Consequently, increasing research interest is being focused on understanding the prognostic and, in particular, the potential therapeutic implications of mutations in genes encoding SWI/SNF subunits. Herein, we review the burgeoning data on the mechanisms by which mutations affecting SWI/SNF complexes promote cancer and describe promising emerging opportunities for targeted therapy, including immunotherapy with immune-checkpoint inhibitors, presented by these mutations. We also highlight ongoing clinical trials open specifically to patients with cancers harbouring mutations in certain SWI/SNF genes.

Molecular markers contribute to the clinical diagnosis for pancreatic cystic neoplasms

A pancreatic cystic neoplasm (PCN) is a rare pancreatic disease. Malignant PCNs are usually identified incidentally while evaluating other lesions. However, PCNs are being identified more frequently owing to the increased use of abdominal imaging. Malignant PCNs have complicated and diverse biological behaviors, including various malignant risk factors, diverse molecular features, natural history, and complex pathological classifications. Although many diagnostic methods, such as cross-sectional imaging and endoscopic evaluation, have been developed, malignant PCNs are still difficult to differentiate from benign tumors. On searching for related articles in the recent decade, we found that some molecular biomarkers such as carcinoembryonic antigen could be useful for discriminating between malignant tumors and benign tumors. However, cytopathologic evaluation is the most useful method for differentiating between benign and malignant lesions. Although cytopathologic evaluation has a specificity of 100% for identifying malignancies, its accuracy is often hampered by the low cellularity of PCN cells in the cystic fluid. Herein, we review the progress in the use of cellular and molecular markers for the accurate identification of PCNs.

The Emerging Roles of ATP-Dependent Chromatin Remodeling Complexes in Pancreatic Cancer

Pancreatic cancer is an aggressive cancer with low survival rates. Genetic and epigenetic dysregulation has been associated with the initiation and progression of pancreatic tumors. Multiple studies have pointed to the involvement of aberrant chromatin modifications in driving tumor behavior. ATP-dependent chromatin remodeling complexes regulate chromatin structure and have critical roles in stem cell maintenance, development, and cancer. Frequent mutations and chromosomal aberrations in the genes associated with subunits of the ATP-dependent chromatin remodeling complexes have been detected in different cancer types. In this review, we summarize the current literature on the genomic alterations and mechanistic studies of the ATP-dependent chromatin remodeling complexes in pancreatic cancer. Our review is focused on the four main subfamilies: SWItch/sucrose non-fermentable (SWI/SNF), imitation SWI (ISWI), chromodomain-helicase DNA-binding protein (CHD), and INOsitol-requiring mutant 80 (INO80). Finally, we discuss potential novel treatment options that use small molecules to target these complexes.

The Use of Genetically Engineered Mouse Models for Studying the Function of Mutated Driver Genes in Pancreatic Cancer

Pancreatic cancer is often treatment-resistant, with the emerging standard of care, gemcitabine, affording only a few months of incrementally-deteriorating survival. Reflecting on the history of failed clinical trials, genetically engineered mouse models (GEMMs) in oncology research provides the inspiration to discover new treatments for pancreatic cancer that come from better knowledge of pathogenesis mechanisms, not only of the derangements in and consequently acquired capabilities of the cancer cells, but also in the aberrant microenvironment that becomes established to support, sustain, and enhance neoplastic progression. On the other hand, the existing mutational profile of pancreatic cancer guides our understanding of the disease, but leaves many important questions of pancreatic cancer biology unanswered. Over the past decade, a series of transgenic and gene knockout mouse modes have been produced that develop pancreatic cancers with features reflective of metastatic pancreatic ductal adenocarcinoma (PDAC) in humans. Animal models of PDAC are likely to be essential to understanding the genetics and biology of the disease and may provide the foundation for advances in early diagnosis and treatment.

SMARCA2-deficiency confers sensitivity to targeted inhibition of SMARCA4 in esophageal squamous cell carcinoma cell lines

SMARCA4/BRG1 and SMARCA2/BRM, the two mutually exclusive catalytic subunits of the BAF complex, display a well-established synthetic lethal relationship in SMARCA4-deficient cancers. Using CRISPR-Cas9 screening, we identify SMARCA4 as a novel dependency in SMARCA2-deficient esophageal squamous cell carcinoma (ESCC) models, reciprocal to the known synthetic lethal interaction. Restoration of SMARCA2 expression alleviates the dependency on SMARCA4, while engineered loss of SMARCA2 renders ESCC models vulnerable to concomitant depletion of SMARCA4. Dependency on SMARCA4 is linked to its ATPase activity, but not to bromodomain function. We highlight the relevance of SMARCA4 as a drug target in esophageal cancer using an engineered ESCC cell model harboring a SMARCA4 allele amenable to targeted proteolysis and identify SMARCA4-dependent cell models with low or absent SMARCA2 expression from additional tumor types. These findings expand the concept of SMARCA2/SMARCA4 paralog dependency and suggest that pharmacological inhibition of SMARCA4 represents a novel therapeutic opportunity for SMARCA2-deficient cancers.

Alteration of Epigenetic Modifiers in Pancreatic Cancer and Its Clinical Implication

The incidence of pancreatic cancer has considerably increased in the past decade. Pancreatic cancer has the worst prognosis among the cancers of the digestive tract because the pancreas is located in the posterior abdominal cavity, and most patients do not show clinical symptoms for early detection. Approximately 55% of all patients are diagnosed with pancreatic cancer only after the tumors metastasize. Therefore, identifying useful biomarkers for early diagnosis and screening high-risk groups are important to improve pancreatic cancer therapy. Recent emerging evidence has suggested that genetic and epigenetic alterations play a crucial role in the molecular aspects of pancreatic tumorigenesis. Here, we summarize recent progress in our understanding of the epigenetic alterations in pancreatic cancer and propose potential synthetic lethal strategies to target these genetic defects to treat this deadly disease.

The Role of ARID1A in Endometrial Cancer and the Molecular Pathways Associated With Pathogenesis and Cancer Progression

AT-rich interaction domain 1A gene (ARID1A) encodes for a subunit of the switch/sucrose non-fermentable (SWI/SNF) complex, a chromatin remodeling complex, and it has been implicated in the pathogenesis of various cancer types. In this review, we discuss how ARID1A is linked to endometrial cancer and what molecular pathways are affected by mutation or inhibition of ARID1A. We also discuss the potential use of ARID1A not only as a prognostic biomarker, but also as a target for therapeutic interventions.

[Pathogenesis and molecular pathology of vestibular schwannoma]

Schwannomas are benign Schwann cell-derived tumors of the peripheral nerve sheath often involving the vestibular cranial nerve (vestibular schwannoma). Histologically, they consist of bipolar spindle cells and show a moderate cellularity. Typically, Antoni A regions with a storiform pattern and loose Antoni B regions are intermingled. Verocay bodies are the pathognomonic palisading structures. Malignant transformation is rare. Merlin (schwannomin), the protein product of NF2, is inactivated by mutations, loss of heterozygosity or methylation. Within neurofibromatosis type 2, a germline mutation is present in about half of cases, whereas tumors demonstrate an additional second hit of the NF2 gene. A loss of chromosome 22 or 22q is common. Merlin links the cell membrane with the cytoskeleton and regulates intracellular signaling pathways leading to dysorganization when merlin is inactivated. Loss of merlin activates Rac1 and Ras, and the PAK1, mTORC1, EGFR-Ras-ERK, PI3K-Akt, WNT and Hippo pathways as well as receptor tyrosine kinases. Furthermore, merlin locates to the nucleus and inhibits E3 ubiquitin ligase CRL4^DCAF1. Besides biallelic inactivation of NF2 in schwannomas, other genes are involved in the pathogenesis of schwannomatosis-associated schwannomas such as LZTR1, SMARCB1, COQ6 indicating an important role of SWI/SNF chromatin-remodeling complex for schwannoma development. Our own investigations point to deregulation of BAF170, another essential SWI/SNF complex component. Knowledge of mechanisms allows targeted molecular therapy, especially in vestibular schwannomas, using antagonists against mTOR (rapamycin/sirolmus/everolimus), EGFR (lapatinib) or VEGF (bevacizumab), although clinical studies have been in part disappointing so far.

The BRG1 ATPase of human SWI/SNF chromatin remodeling enzymes as a driver of cancer

Mammalian SWI/SNF enzymes are ATP-dependent remodelers of chromatin structure. These multisubunit enzymes are heterogeneous in composition; there are two catalytic ATPase subunits, BRM and BRG1, that are mutually exclusive, and additional subunits are incorporated in a combinatorial manner. Recent findings indicate that approximately 20% of human cancers contain mutations in SWI/SNF enzyme subunits, leading to the conclusion that the enzyme subunits are critical tumor suppressors. However, overexpression of specific subunits without apparent mutation is emerging as an alternative mechanism by which cellular transformation may occur. Here we highlight recent evidence linking elevated expression of the BRG1 ATPase to tissue-specific cancers and work suggesting that inhibiting BRG1 may be an effective therapeutic strategy.

Diversity of Precursor Lesions For Pancreatic Cancer: The Genetics and Biology of Intraductal Papillary Mucinous Neoplasm

Pancreatic ductal adenocarcinoma (PDA), one of the most lethal cancers worldwide, is associated with two main types of morphologically distinct precursors—pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasm (IPMN). Although the progression of PanIN into invasive cancer has been well characterized, there remains an urgent need to understand the biology of IPMNs, which are larger radiographically detectable cystic tumors. IPMNs comprise a number of subtypes with heterogeneous histopathologic and clinical features. Although frequently remaining benign, a significant proportion exhibits malignant progression. Unfortunately, there are presently no accurate prognosticators for assessing cancer risk in individuals with IPMN. Moreover, the fundamental mechanisms differentiating PanIN and IPMN remain largely obscure, as do those that distinguish IPMN subtypes. Recent studies, however, have identified distinct genetic profiles between PanIN and IPMN, providing a framework to better understand the diversity of the precursors for PDA. Here, we review the clinical, biological, and genetic properties of IPMN and discuss various models for progression of these tumors to invasive PDA.

Mammalian SWI/SNF complexes in cancer: emerging therapeutic opportunities

Mammalian SWI/SNF (BAF) chromatin remodeling complexes orchestrate a diverse set of chromatin alterations which impact transcriptional output. Recent whole-exome sequencing efforts have revealed that the genes encoding subunits of mSWI/SNF complexes are mutated in over 20% of cancers, spanning a wide range of tissue types. The majority of mutations result in loss of subunit protein expression, implicating mSWI/SNF subunits as tumor suppressors. mSWI/SNF-deficient cancers remain a therapeutic challenge, owing to a lack of potent and selective agents which target complexes or unique pathway dependencies generated by mSWI/SNF subunit perturbations. Here, we review the current landscape of mechanistic insights and emerging therapeutic opportunities for human malignancies driven by mSWI/SNF complex perturbation.

Expression of BRG1 in colorectal cancer: Correlation with prognosis and MMP-2 expression

AIM

To analyze the relationship of the expression of BRG1 with clinicopathologic characters and prognosis of colorectal cancer.

METHODS

Tissue microarray and immunohistochemical method were used to detect the expression of BRG1 in 112 cases of colorectal cancer and 71 cases of matched normal intestinal mucosa tissue. The relationship of BRG1 expression with clinicopathologic characters, prognosis, and matrix metalloproteinase-2 (MMP-2) expression was statistically analyzed.

RESULTS

The positive expression rate of BRG1 in colorectal cancer was significantly higher than that in normal intestine mucosa tissue (66.1% vs 35.2%, P < 0.01). The positive expression rate of MMP-2 was also significantly higher in colorectal cancer than in normal intestine mucosa tissue (61.2% vs 3.3%, P < 0.01). The expression of BRG1 showed no significant correlation with clinicopathologic characters including gender, age, tumor size, invasive depth, differentiation degree, lymph node metastasis, and clinical stage, but was significantly correlated with 5-year survival rate of colorectal cancer patients. The prognosis of colorectal cancer patients with high BRG1 expression was much worse than that of patients with low BRG1 expression. There was a positive correlation between BRG1 and MMP-2 expression (r = 0.307, P < 0.05).

CONCLUSION

BRG1 is highly expressed in colorectal cancer tissue. BRG1 is an independent prognostic factor in colorectal cancer. Increased expression of MMP-2 may be a probable reason of worse prognosis of colorectal cancer.

Pancreatic Cancer, A Mis-interpreter of the Epigenetic Language

Pancreatic cancer is the third leading cause of cancer mortality in the U.S. with close to 40,000 deaths per year. Pancreatic ductal adenocarcinoma (PDAC) represents approximately 90 percent of all pancreatic cancer cases and is the most lethal form of the disease. Current therapies for PDAC are ineffective and most patients cannot be treated by surgical resection. Most research efforts have primarily focused on how genetic alterations cause, alter progression, contribute to diagnosis, and influence PDAC management. Over the past two decades, a model has been advanced of PDAC initiation and progression as a multi-step process driven by the acquisition of mutations leading to loss of tumor suppressors and activation of oncogenes. The recognition of the essential roles of these genetic alterations in the development of PDAC has revolutionized our knowledge of this disease. However, none of these findings have turned into effective treatment for this dismal malignancy. In recent years, studies in the areas of chromatin modifications, and non-coding RNAs have uncovered mechanisms for regulating gene expression which occur independently of genetic alterations. Chromatin-based mechanisms are interwoven with microRNA-driven regulation of protein translation to create an integrated epigenetic language, which is grossly dysregulated in PDAC. Thus in PDAC, key tumor suppressors that are well established to play a role in PDAC may be repressed, and oncogenes can be upregulated secondary to epigenetic alterations. Unlike mutations, epigenetic changes are potentially reversible. Given this feature of epigenetic mechanisms, it is conceivable that targeting epigenetic-based events promoting and maintaining PDAC could serve as foundation for the development of new therapeutic and diagnostic approaches for this disease.

GLI1, a master regulator of the hallmark of pancreatic cancer

Hedgehog signaling is highly conserved across species and governs proper embryonic development. Germline gene mutations that reduce this signaling activity cause a variety of developmental abnormalities such as holoprosencephaly, while those that enhance Hedgehog signaling activity induce a tumor-predisposition condition Nevoid basal cell carcinoma syndrome. Furthermore, dysregulated activation of Hedgehog signaling has been recognized in various sporadic malignancies, including pancreatic adenocarcinoma. Pancreatic adenocarcinoma develops through a multistep carcinogenesis starting with oncogenic mutation of the KRAS gene. During this process, precancerous or cancer cells secrete Hedgehog ligand proteins to promote characteristic desmoplastic stroma around the cells, which in turn activates the expression of the downstream transcription factor GLI1 inside the cells. The quantitative and spatiotemporal dysregulation of GLI1 subsequently leads to the expression of transcriptional target genes of GLI1 that govern the hallmark of malignant properties. Here, after a brief introductory outline, a perspective is offered of Hedgehog signaling with a special focus on the role of GLI1 in pancreatic carcinogenesis.

TGF-β1 promotes acinar to ductal metaplasia of human pancreatic acinar cells

Animal studies suggest that pancreatitis-induced acinar-to-ductal metaplasia (ADM) is a key event for pancreatic ductal adenocarcinoma (PDAC) initiation. However, there has not been an adequate system to explore the mechanisms of human ADM induction. We have developed a flow cytometry-based, high resolution lineage tracing method and 3D culture system to analyse ADM in human cells. In this system, well-known mouse ADM inducers did not promote ADM in human cells. In contrast, TGF-β1 efficiently converted human acinar cells to duct-like cells (AD) in a SMAD-dependent manner, highlighting fundamental differences between the species. Functionally, AD cells gained transient proliferative capacity. Furthermore, oncogenic KRAS did not induce acinar cell proliferation, but did sustain the proliferation of AD cells, suggesting that oncogenic KRAS requires ADM-associated-changes to promote PDAC initiation. This ADM model provides a novel platform to explore the mechanisms involved in the development of human pancreatic diseases.

Selecting optimal surgical procedures for intraductal papillary mucinous neoplasm (IPMN): An analysis based on the Surveillance, Epidemiology, and End Result registry database

INTRODUCTION

Intraductal papillary mucinous neoplasm (IPMN) is a field defect disease of pancreas that has malignant potential. Many studies have recommended surgery as the preferred treatment. We investigated whether a total pancreatectomy (TP) can improve patient prognosis compared to a pancreatoduodenectomy (PD) and the indications for each approach.

PATIENTS AND METHODS

We obtained data of 548 malignant IPMN patients who underwent either a TP or a PD from SEER database. The survival rates were analyzed using the Kaplan-Meier method and a Cox regression model. Cases were subdivided to investigate the advantages of each procedure.

RESULTS

The surgical procedures (PD and TP) did not significantly affect either cancer-specific survival (CSS) times or overall survival (OS) times in both Kaplan-Meier analysis and Cox regression (Kaplan-Meier: PCSS = 0.919, POS = 0.996; Cox: PCSS = 0.735, POS = 0.820). In the subgroup analyses, patients in stage T4 and AJCC stage III in the TP group had a longer survival time than did those in the PD group (33 months vs 14 months), but not significant (T4: PCSS = 0.124, AJCC III: PCSS = 0.102). In addition, PD had the trend to be better for poorly differentiated patients (Pos = 0.055) and older patients.

CONCLUSION

TP did not offer any significant OS and CSS benefits as compared to PD. However, for patients in stage T4 and AJCC stage III, TP may extend survival time in some degree. In older or histologically poorly differentiated patients, PD may be preferable to TP. The results are rational, but still warrant further verification due to limited sample volumes of specific subgroups.

Brg1 promotes both tumor-suppressive and oncogenic activities at distinct stages of pancreatic cancer formation

Pancreatic Ductal Adenocarcinoma (PDA) develops predominantly through pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasm (IPMN) precursor lesions. Roy et al. identify critical antagonistic roles for Brg1, a catalytic subunit of the SWI/SNF complexes, during IPMN-PDA development. In mature duct cells Brg1 inhibits the dedifferentiation that precedes neoplastic transformation. In contrast, Brg1 promotes tumorigenesis in full-blown PDA by supporting a mesenchymal-like transcriptional landscape. JQ1 impairs PDA tumorigenesis by both mimicking some and inhibiting other Brg1-mediated functions.

Pancreatic ductal adenocarcinoma (PDA) develops predominantly through pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasm (IPMN) precursor lesions. Pancreatic acinar cells are reprogrammed to a “ductal-like” state during PanIN-PDA formation. Here, we demonstrate a parallel mechanism operative in mature duct cells during which functional cells undergo “ductal retrogression” to form IPMN-PDA. We further identify critical antagonistic roles for Brahma-related gene 1 (Brg1), a catalytic subunit of the SWI/SNF complexes, during IPMN-PDA development. In mature duct cells, Brg1 inhibits the dedifferentiation that precedes neoplastic transformation, thus attenuating tumor initiation. In contrast, Brg1 promotes tumorigenesis in full-blown PDA by supporting a mesenchymal-like transcriptional landscape. We further show that JQ1, a drug that is currently being tested in clinical trials for hematological malignancies, impairs PDA tumorigenesis by both mimicking some and inhibiting other Brg1-mediated functions. In summary, our study demonstrates the context-dependent roles of Brg1 and points to potential therapeutic treatment options based on epigenetic regulation in PDA.

Pancreatic adenocarcinoma pathology: changing "landscape"

Pancreatic cancer is a devastating disease. At time of diagnosis the disease is usually advanced and only a minority of patients are eligible for surgical resection. The overall 5-year survival is 6%. However, survival of patients with early stage pancreatic cancer is significantly better. To improve the prognosis of patients with pancreatic cancer, it is essential to diagnose and treat pancreatic cancer in the earliest stage. Prevention of pancreatic cancer by treating noninvasive precursor lesions just before they invade tissues can potentially lead to even better outcomes. Pancreatic carcinogenesis results from a stepwise progression in which accumulating genetic alterations drive neoplastic progression in well-defined precursor lesions, ultimately giving rise to an invasive adenocarcinoma. A thorough understanding of the genetic changes that drive pancreatic carcinogenesis can lead to identification of biomarkers for early detection and targets for therapy. Recent next-generation sequencing (NGS) studies have shed new light on our understanding of the natural history of pancreatic cancer and the precursor lesions that give rise to these cancers. Importantly, there is a significant window of opportunity for early detection and treatment between the first genetic alteration in a cell in the pancreas and development of full-blown pancreatic cancer. The current views on the pathology and genetics of pancreatic carcinogenesis that evolved from studies of pancreatic cancer and its precursor lesions are discussed in this review.

Cytosine deamination is a major cause of baseline noise in next-generation sequencing

BACKGROUND AND OBJECTIVES

As next-generation sequencing (NGS) becomes a major sequencing platform in clinical diagnostic laboratories, it is critical to identify artifacts that constitute baseline noise and may interfere with detection of low-level gene mutations. This is especially critical for applications requiring ultrasensitive detection, such as molecular relapse of solid tumors and early detection of cancer. We recently observed a ~10-fold higher frequency of C:G > T:A mutations than the background noise level in both wild-type peripheral blood and formalin-fixed paraffin-embedded samples. We hypothesized that these might represent cytosine deamination events, which have been seen using other platforms.

METHODS

To test this hypothesis, we pretreated samples with uracil N-glycosylase (UNG). Additionally, to test whether some of the cytosine deamination might be a laboratory artifact, we simulated the heat associated with polymerase chain reaction thermocycling by subjecting samples to thermocycling in the absence of polymerase. To test the safety of universal UNG pretreatment, we tested known positive samples treated with UNG.

RESULTS

UNG pretreatment significantly reduced the frequencies of these mutations, consistent with a biologic source of cytosine deamination. The simulated thermocycling-heated samples demonstrated significantly increased frequencies of C:G > T:A mutations without other baseline base substitutions being affected. Samples with known mutations demonstrated no decrease in our ability to detect these after treatment with UNG.

CONCLUSION

Baseline noise during NGS is mostly due to cytosine deamination, the source of which is likely to be both biologic and an artifact of thermocycling, and it can be reduced by UNG pretreatment.

Molecular mechanism of intraductal papillary mucinous neoplasm and intraductal papillary mucinous neoplasm-derived pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal human malignancies. Dissecting the mechanisms underlying PDA development is important for developing early detection methods and effective prevention and therapies for the disease. PDA is considered to arise from distinct precursor lesions, including pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasia (IPMN). However, little is known about molecular mechanisms of development of IPMN and IPMN-derived PDA. We have recently reported that loss of Brg1, a core subunit of SWI/SNF chromatin remodeling complexes, cooperates with oncogenic Kras to form cystic neoplastic lesions that resemble human IPMN and progress to PDA. Brg1 null IPMN-PDA is less lethal compared to PanIN-derived PDA (PanIN-PDA) driven by mutant Kras and hemizygous p53 deletion, mirroring prognostic trends in PDA patients. Brg1 null IPMN-PDA possesses a distinct molecular signature that supports less malignant potential compared to PanIN-PDA. Furthermore, Brg1 deletion inhibits Kras-dependent PanIN development from adult acinar cells, but promotes Kras-driven preneoplastic transformation in adult duct cells. Therefore, Brg1 is a determinant of context-dependent Kras-driven pancreatic tumorigenesis and chromatin remodeling may underlie the development of distinct PDA subsets. Understanding molecular mechanism of IPMN and IPMN-derived PDA could provide critical clues for novel diagnostic and therapeutic strategies of the disease.

Beyond Mutations: Additional Mechanisms and Implications of SWI/SNF Complex Inactivation

SWI/SNF is a major regulator of gene expression. Its role is to facilitate the shifting and exposure of DNA segments within the promoter and other key domains to transcription factors and other essential cellular proteins. This complex interacts with a wide range of proteins and does not function within a single, specific pathway; thus, it is involved in a multitude of cellular processes, including DNA repair, differentiation, development, cell adhesion, and growth control. Given SWI/SNF's prominent role in these processes, many of which are important for blocking cancer development, it is not surprising that the SWI/SNF complex is targeted during cancer initiation and progression both by mutations and by non-mutational mechanisms. Currently, the understanding of the types of alterations, their frequency, and their impact on the SWI/SNF subunits is an area of intense research that has been bolstered by a recent cadre of NextGen sequencing studies. These studies have revealed mutations in SWI/SNF subunits, indicating that this complex is thus important for cancer development. The purpose of this review is to put into perspective the role of mutations versus other mechanisms in the silencing of SWI/SNF subunits, in particular, BRG1 and BRM. In addition, this review explores the recent development of synthetic lethality and how it applies to this complex, as well as how BRM polymorphisms are becoming recognized as potential clinical biomarkers for cancer risk.

SIGNIFICANCE

Recent reviews have detailed the occurrence of mutations in nearly all SWI/SNF subunits, which indicates that this complex is an important target for cancer. However, when the frequency of mutations in a given tumor type is compared to the frequency of subunit loss, it becomes clear that other non-mutational mechanisms must play a role in the inactivation of SWI/SNF subunits. Such data indicate that epigenetic mechanisms that are known to regulate BRM may also be involved in the loss of expression of other SWI/SNF subunits. This is important since epigenetically silenced genes are inducible, and thus, the reversal of the silencing of these non-mutationally suppressed subunits may be a viable mode of targeted therapy.

Topoisomerase IIα in chromosome instability and personalized cancer therapy

Genome instability is a hallmark of cancer cells. Chromosome instability (CIN), which is often mutually exclusive from hypermutation genotypes, represents a distinct subtype of genome instability. Hypermutations in cancer cells are due to defects in DNA repair genes, but the cause of CIN is still elusive. However, because of the extensive chromosomal abnormalities associated with CIN, its cause is likely a defect in a network of genes that regulate mitotic checkpoints and chromosomal organization and segregation. Emerging evidence has shown that the chromosomal decatenation checkpoint, which is critical for chromatin untangling and packing during genetic material duplication, is defective in cancer cells with CIN. The decatenation checkpoint is known to be regulated by a family of enzymes called topoisomerases. Among them, the gene encoding topoisomerase IIα (TOP2A) is commonly altered at both gene copy number and gene expression level in cancer cells. Thus, abnormal alterations of TOP2A, its interacting proteins, and its modifications may play a critical role in CIN in human cancers. Clinically, a large arsenal of topoisomerase inhibitors have been used to suppress DNA replication in cancer. However, they often lead to the secondary development of leukemia because of their effect on the chromosomal decatenation checkpoint. Therefore, topoisomerase drugs must be used judiciously and administered on an individual basis. In this review, we highlight the biological function of TOP2A in chromosome segregation and the mechanisms that regulate this enzyme's expression and activity. We also review the roles of TOP2A and related proteins in human cancers, and raise a perspective for how to target TOP2A in personalized cancer therapy.

SWI/SNF chromatin remodeling complexes and cancer

The identification of mutations and deletions in the SMARCB1 locus in chromosome band 22q11.2 in pediatric rhabdoid tumors provided the first evidence for the involvement of the SWI/SNF chromatin remodeling complex in cancer. Over the last 15 years, alterations in more than 20 members of the complex have been reported in a variety of human tumors. These include germline mutations and copy number alterations in SMARCB1, SMARCA4, SMARCE1, and PBRM1 that predispose carriers to both benign and malignant neoplasms. Somatic mutations, structural abnormalities, or epigenetic modifications that lead to reduced or aberrant expression of complex members have now been reported in more than 20% of malignancies, including both solid tumors and hematologic disorders in both children and adults. In this review, we will highlight the role of SMARCB1 in cancer as a paradigm for other tumors with alterations in SWI/SNF complex members and demonstrate the broad spectrum of mutations observed in complex members in different tumor types.

Molecular pathology of intraductal papillary mucinous neoplasms of the pancreas

Since the first description of intraductal papillary mucinous neoplasms (IPMNs) of the pancreas in the eighties, their identification has dramatically increased in the last decades, hand to hand with the improvements in diagnostic imaging and sampling techniques for the study of pancreatic diseases. However, the heterogeneity of IPMNs and their malignant potential make difficult the management of these lesions. The objective of this review is to identify the molecular characteristics of IPMNs in order to recognize potential markers for the discrimination of more aggressive IPMNs requiring surgical resection from benign IPMNs that could be observed. We briefly summarize recent research findings on the genetics and epigenetics of intraductal papillary mucinous neoplasms, identifying some genes, molecular mechanisms and cellular signaling pathways correlated to the pathogenesis of IPMNs and their progression to malignancy. The knowledge of molecular biology of IPMNs has impressively developed over the last few years. A great amount of genes functioning as oncogenes or tumor suppressor genes have been identified, in pancreatic juice or in blood or in the samples from the pancreatic resections, but further researches are required to use these informations for clinical intent, in order to better define the natural history of these diseases and to improve their management.

BRG1 promotes chemoresistance of pancreatic cancer cells through crosstalking with Akt signalling

Gemcitabine is a standard chemotherapeutic agent for locally advanced and metastatic pancreatic cancer. However, the chemoresistance of pancreatic cancer is the major barrier to efficient chemotherapy. Here, we reported that BRG1, a chromatin modulator, was exclusively overexpressed in human pancreatic ductal adenocarcinoma tissues. BRG1 knockdown inhibited PANC-1 and MIA PaCa-2 cell growth in vitro and in vivo, reduced the phosphorylation/activation of Akt and p21(cip/waf), enhanced intrinsic and gemcitabine induced apoptosis and attenuated gemcitabine-induced downregulation of E-cadherin. Moreover, by establishing acquired chemoresistance of MIA PaCa-2 cells in vitro, we found that BRG1 knockdown effectively reversed the chemoresistance to gemcitabine. Surprisingly, inhibiting Akt phosphorylation resulted in BRG1 suppression in pancreatic cancer cells, indicating BRG1 as a new downstream target of Akt signalling. Taken together, our findings suggest that BRG1 promotes both intrinsic and acquired chemoresistance of pancreatic cancer cells, and BRG1 crosstalks with Akt signalling to form a positive feedback loop to promote pancreatic cancer development.

Clinical validation of KRAS, BRAF, and EGFR mutation detection using next-generation sequencing

OBJECTIVES

To validate next-generation sequencing (NGS) technology for clinical diagnosis and to determine appropriate read depth.

METHODS

We validated the KRAS, BRAF, and EGFR genes within the Ion AmpliSeq Cancer Hotspot Panel using the Ion Torrent Personal Genome Machine (Life Technologies, Carlsbad, CA).

RESULTS

We developed a statistical model to determine the read depth needed for a given percent tumor cellularity and number of functional genomes. Bottlenecking can result from too few input genomes. By using 16 formalin-fixed, paraffin-embedded (FFPE) cancer-free specimens and 118 cancer specimens with known mutation status, we validated the six traditional analytic performance characteristics recommended by the Next-Generation Sequencing: Standardization of Clinical Testing Working Group. Baseline noise is consistent with spontaneous and FFPE-induced C:G→T:A deamination mutations.

CONCLUSIONS

Redundant bioinformatic pipelines are essential, since a single analysis pipeline gave false-negative and false-positive results. NGS is sufficiently robust for the clinical detection of gene mutations, with attention to potential artifacts.

Genetic variants in the SWI/SNF complex and smoking collaborate to modify the risk of pancreatic cancer in a Chinese population

Pancreatic cancer (PC) is an aggressive malignancy with extremely low 5-year survival rate (<5%). SWItch/Sucrose Non Fermentable (SWI/SNF) complex is a core factor for chromatin-remodeling that utilize energy of ATP hydrolysis to mobilize nucleosomes, and modulate gene transcription. Recent studies have identified recurrent mutations in major components of SWI/SNF in a variety of human cancers, including PC. We conducted a two-stage case-control study to investigate the associations between 14 common variants in 6 genes (SMARCA4, SMCRB1, PBRM1, BRD7, ARID1, and ARID2) encoding major components of the SWI/SNF complex and the risk of PC. Three promising variants, rs11644043, rs11085754, and rs2073389 in the discovery stage comprising 310 cases and 457 controls were further genotyped in the validation stage containing 429 cases and 585 controls. rs11644043 in BRD7 and rs11085754 in SMARCA4 showed consistent significant association with increased risk of PC in both stages, with odds ratios (ORs) and 95% confidence interval (CI) of 2.04 (1.17-3.56) and 1.64 (1.16-2.33) in stage one, and 1.97 (1.24-3.14) and 1.45 (1.04-2.02) in stage two, respectively in a recessive model. Furthermore, the accumulative effects of rs11644043, rs11085754, and rs2073389 in SMARCB1 were observed (P for trend <0.0001). Intriguingly, gene-environmental interactions analysis consistently revealed the potential interactions of rs2073389 (P(add)  - FDR = 6.00 × 10(-4), P(mul)  - FDR = 1.50 × 10(-2)) and rs11085754 (P(add)  - FDR = 0.03) collaborating with smoking to modify the risk of PC. In conclusion, the current study provides evidence that genetic variants of SWI/SNF may contribute to the susceptibility of PC in the Chinese population.

The chromatin regulator Brg1 suppresses formation of intraductal papillary mucinous neoplasm and pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) develops through distinct precursor lesions, including pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasia (IPMN). However, genetic features resulting in IPMN-associated PDA (IPMN-PDA) versus PanIN-associated PDA (PanIN-PDA) are largely unknown. Here we find that loss of Brg1, a core subunit of SWI/SNF chromatin remodelling complexes, cooperates with oncogenic Kras to form cystic neoplastic lesions that resemble human IPMN and progress to PDA. Although Brg1-null IPMN-PDA develops rapidly, it possesses a distinct transcriptional profile compared with PanIN-PDA driven by mutant Kras and hemizygous p53 deletion. IPMN-PDA also is less lethal, mirroring prognostic trends in PDA patients. In addition, Brg1 deletion inhibits Kras-dependent PanIN development from adult acinar cells, but promotes Kras-driven preneoplastic transformation in adult duct cells. Therefore, this study implicates Brg1 as a determinant of context-dependent Kras-driven pancreatic tumorigenesis and suggests that chromatin remodelling may underlie the development of distinct PDA subsets.

Loss of ARID1A expression and its relationship with PI3K-Akt pathway alterations, TP53 and microsatellite instability in endometrial cancer

The switch/sucrose non-fermentable (SWI/SNF) subunit ARID1A (AT-rich interactive domain 1A gene) has been recently postulated as a novel tumor suppressor of gynecologic cancer and one of the driver genes in endometrial carcinogenesis. However, specific relationships with established molecular alterations in endometrioid endometrial cancer (EEC) are currently unknown. We analyzed the expression of ARID1A in 146 endometrial cancers (130 EECs and 16 non-EECs) in relation to alterations in the PI3K-Akt pathway (PTEN expression/KRAS/PIK3CA mutations), TP53 status (TP53 immunohistochemistry) and microsatellite instability. To discriminate between microsatellite instability due to somatic MLH1 promoter hypermethylation or germline mutations in one of the mismatch repair genes (Lynch syndrome), we included a 'Lynch syndrome set'. This set included 21 cases with confirmed germline mutations and 15 cases that were suspected to have a germline mutation. Loss of ARID1A expression was exclusively found in EECs in 31% (40/130) of the EEC cases. No loss of expression of the other subunits of the SWI/SNF complex, SMARCD3 and SMARCB1, was detected. Alterations in the PI3K-Akt pathway were more frequent when ARID1A expression was lost. Loss of ARID1A and mutant-like TP53 expression was nearly mutually exclusive (P=0.0004). In contrast to Lynch-associated tumors, a strong association between ARID1A loss and sporadic microsatellite instability was found. Only five cases (14%) of the 'Lynch syndrome set' as compared with 24 cases (75%, P<0.0001) of the sporadic microsatellite-unstable tumors showed loss of ARID1A. These observations suggest that ARID1A is a causative gene, instead of a target gene, of microsatellite instability by having a role in epigenetic silencing of the MLH1 gene in endometrial cancer.

Intraductal papillary mucinous neoplasms of the pancreas: is the puzzle solved?

Intraductal papillary mucinous neoplasms (IPMN) are drawing more attention and being detected more frequently. This review focuses on current understanding of the management of IPMN, regarding morphological classification, subclassification by cell lineage features, molecular abnormalities, radiological and imaging evaluation, progression to cancer, incidence and risk factors for malignancy, risk of distinct pancreatic adenocarcinoma and extrapancreatic malignancies, treatment strategy, and types of surgical resection. In particular, missing links in solving the IPMN puzzles are described with regard to differential diagnosis, role of cyst fluid analysis, multifocal IPMN, histological evaluation of the surgical specimen, observation without resection, follow up of patients after resection, role of adjuvant therapy for invasive carcinoma, screening for other neoplasms in patients with IPMN on follow up, prognostic factors influencing long-term outcomes, and role of endoscopic therapy.

BRG1 is a prognostic marker and potential therapeutic target in human breast cancer

BRG1, a core component of the SWI/SNF chromatin-remodeling complex, has been implicated in cancer development; however, the biological significance of BRG1 in breast cancer remains unknown. We explored the role of BRG1 in human breast cancer pathogenesis. Using tissue microarray and immunohistochemistry, we evaluated BRG1 staining in 437 breast cancer specimens and investigated its role in breast cancer cell proliferation, migration and invasion. Our Kaplan-Meier survival curves showed that high BRG1 expression is inversely correlated with both overall (P = 0.000) and disease-specific (P = 0.000) 5-year patient survival. Furthermore, we found that knockdown of BRG1 by RNA interference markedly inhibits cell proliferation and causes cessation of cell cycle. This reduced cell proliferation is due to G1 phase arrest as cyclin D1 and cyclin E are diminished whereas p27 is upregulated. Moreover, BRG1 depletion induces the expression of TIMP-2 but reduces MMP-2, thereby inhibiting the ability of cells to migrate and to invade. These results highlight the importance of BRG1 in breast cancer pathogenesis and BRG1 may serve as a prognostic marker as well as a potentially selective therapeutic target.

Is it necessary to follow patients after resection of a benign pancreatic intraductal papillary mucinous neoplasm?

BACKGROUND

Little is known about the risk of subsequently developing a new or progressive intraductal papillary mucinous neoplasm (IPMN) after partial pancreatic resection of a noninvasive IPMN.

STUDY DESIGN

One hundred thirty patients with more than 1 year of follow-up after resection were included in this analysis.

RESULTS

At a median follow-up of 38 months, 22 (17%) developed imaging evidence of a new or progressive IPMN. Eleven (8%) underwent completion resection. Three of the 11 patients had invasive adenocarcinoma. Two other patients developed metastatic pancreatic adenocarcinoma and did not undergo resection. All 5 patients (4%) with cancer had negative margins at initial operation. Sixteen of 100 patients (16%) with negative margins for IPMN at the initial operation developed a new IPMN vs 6 of 30 patients (20%) with margins positive for IPMN (p = ns). Five of 22 patients (23%) with a new IPMN had a family history of pancreatic cancer, while 8 of 108 patients (7%) without a new IPMN had a family history (p < 0.05). Overall, the chances of developing a new IPMN at 1, 5, and 10 years after the initial surgery were 4%, 25%, and 62%, respectively, and of requiring surgery were 1.6%, 14%, and 18%, respectively. The estimated chances of developing invasive pancreatic cancer were 0%, 7%, and 38% at 1, 5, and 10 years, respectively.

CONCLUSIONS

Patients who have undergone resection for noninvasive IPMN require indefinite close surveillance because of the risks of developing a new IPMN, of requiring surgery, and of developing cancer. A family history of pancreatic cancer, but not margin status or degree of dysplasia, is associated with a risk of development of a new or progressive IPMN.

The spectrum of SWI/SNF mutations, ubiquitous in human cancers

SWI/SNF is a multi-subunit chromatin remodeling complex that uses the energy of ATP hydrolysis to reposition nucleosomes, thereby modulating gene expression. Accumulating evidence suggests that SWI/SNF functions as a tumor suppressor in some cancers. However, the spectrum of SWI/SNF mutations across human cancers has not been systematically investigated. Here, we mined whole-exome sequencing data from 24 published studies representing 669 cases from 18 neoplastic diagnoses. SWI/SNF mutations were widespread across diverse human cancers, with an excess of deleterious mutations, and an overall frequency approaching TP53 mutation. Mutations occurred most commonly in the SMARCA4 enzymatic subunit, and in subunits thought to confer functional specificity (ARID1A, ARID1B, PBRM1, and ARID2). SWI/SNF mutations were not mutually-exclusive of other mutated cancer genes, including TP53 and EZH2 (both previously linked to SWI/SNF). Our findings implicate SWI/SNF as an important but under-recognized tumor suppressor in diverse human cancers, and provide a key resource to guide future investigations.

Intraductal papillary mucinous neoplasm of the pancreas: an update

Intraductal papillary mucinous neoplasm (IPMN) is a cystic tumor of the pancreas. The etiology is unknown, but increasing evidence suggests the involvement of several tumorigenesis pathways, including an association with hereditary syndromes. IPMN occurs more commonly in men, with the mean age at diagnosis between 64 and 67 years old. At the time of diagnosis, it may be benign, with or without dysplasia, or frankly malignant with an invasive carcinoma. Tumors arising from the main pancreatic duct are termed main-duct IPMNs, those involving the branch ducts, branch-duct IPMNs. In general, small branch-duct IPMNs are benign, particularly in asymptomatic patients, and can be safely followed. In contrast, main-duct tumors should be surgically resected and examined carefully for an invasive component. In the absence of invasion, patient's survival is excellent, from 94 to 100%. For patients with an IPMN-associated invasive carcinoma, the prognosis overall is better than those with a de novo pancreatic ductal adenocarcinoma, with a 5-year survival of 40% to 60% in some series. However, no survival advantage can be demonstrated if the invasive component in an IPMN patient is that of the conventional tubular type (versus mucinous carcinoma). Several histomorphologic variants are recognized, although the clinical significance of this "subtyping" is not well defined.

Insights into the epigenetic mechanisms controlling pancreatic carcinogenesis

During the last couple decades, we have significantly advanced our understanding of mechanisms underlying the development of pancreatic ductual adenocarcinoma (PDAC). In the late 1990s into the early 2000s, a model of PDAC development and progression was developed as a multi-step process associated with the accumulation of somatic mutations. The correlation and association of these particular genetic aberrations with the establishment and progression of PDAC has revolutionized our understanding of this process. However, this model leaves out other molecular events involved in PDAC pathogenesis that contribute to its development and maintenance, specifically those being epigenetic events. Thus, a new model considering the new scientific paradigms of epigenetics will provide a more comprehensive and useful framework for understanding the pathophysiological mechanisms underlying this disease. Epigenetics is defined as the type of inheritance not based on a particular DNA sequence but rather traits that are passed to the next generation via DNA and histone modifications as well as microRNA-dependent mechanisms. Key tumor suppressors that are well established to play a role in PDAC may be altered through hypermethylation, and oncogenes can be upregulated secondary to permissive histone modifications. Factors involved in tumor invasiveness can be aberrantly expressed through dysregulated microRNAs. A noteworthy characteristic of epigenetic-based inheritance is its reversibility, which is in contrast to the stable nature of DNA sequence-based alterations. Given this nature of epigenetic alterations, it becomes imperative that our understanding of epigenetic-based events promoting and maintaining PDAC continues to grow.