Expression of keratin 5 as a distinctive feature of epithelial and biphasic mesotheliomas. An immunohistochemical study using monoclonal antibody AE14

Pleural Mesothelioma: Current Practice and Approach

Pleural mesotheliomas represent one of the most common diagnostic challenges in thoracic pathology. The diagnosis of pleural mesothelioma weighs heavily on clinical and radiologic information. In addition, in the past, before the era of immunohistochemistry, the diagnosis was aided with the use of special histochemical stains-PAS, D-PAS, and mucicarmine, which now very much have been replaced by immunohistochemical stains. In the era of immunohistochemistry, a combination of carcinomatous epitopes and positive mesothelioma markers has become paramount in the diagnosis of mesothelioma, and more recently the use of molecular techniques has become another ancillary tool in supporting such a diagnosis. At the same time, the treatment and clinical outcome of these patients may in some measure be determined by the histopathological features of the tumor and one that also over the years has changed from a palliative type to surgery, chemotherapy, radiotherapy, or a combination of these types. The histopathological growth patterns of mesothelioma are also wide, and in some cases may mimic other tumors that may be primary or metastatic to the pleura. Therefore, the assessment of the diagnosis of mesothelioma is one that requires a global view of the different factors including clinical, radiologic, pathologic-including immunohistochemistry and molecular diagnosis.

Skin-on-a-chip strategies for human hair follicle regeneration

The number of hair loss patients increases every year, and hair loss treatment has several limitations, so research on hair is attracting attention recently. However, most current hair follicle research models are limited by their inability to replicate several key functions of the hair follicle microenvironment. To complement this, an in vitro culture system similar to the in vivo environment must be constructed. It is necessary to develop a hair-on-a-chip that implements a fully functional hair follicle model by reproducing the main characteristics of hair follicle morphogenesis and cycle. In this review, we summarize the gradation of hair follicle morphogenesis and the roles and mechanisms of molecular signals involved in the hair follicle cycle. In addition, we discuss research results of various in vitro organoid products and organ-on-a-chip-based hair follicle tissue chips for the treatment of alopecia and present future research and development directions.

Transcriptomic and Functional Evidence Show Similarities between Human Amniotic Epithelial Stem Cells and Keratinocytes

Amniotic epithelial stem cells (AESCs) are considered as potential alternatives to keratinocytes (KCs) in tissue-engineered skin substitutes used for treating skin damage. However, their clinical application is limited since similarities and distinctions between AESCs and KCs remain unclear. Herein, a transcriptomics analysis and functional evaluation were used to understand the commonalities and differences between AESCs and KCs. RNA-sequencing revealed that AESCs are involved in multiple epidermis-associated biological processes shared by KCs and show more similarity to early stage immature KCs than to adult KCs. However, AESCs were observed to be heterogeneous, and some possessed hybrid mesenchymal and epithelial features distinct from KCs. A functional evaluation revealed that AESCs can phagocytose melanosomes transported by melanocytes in both 2D and 3D co-culture systems similar to KCs, which may help reconstitute pigmented skin. The overexpression of TP63 and activation of NOTCH signaling could promote AESC stemness and improve their differentiation features, respectively, bridging the gap between AESCs and KCs. These changes induced the convergence of AESC cell fate with KCs. In future, modified reprogramming strategies, such as the use of small molecules, may facilitate the further modulation human AESCs for use in skin regeneration.

Keratins as an Inflammation Trigger Point in Epidermolysis Bullosa Simplex

Epidermolysis bullosa simplex (EBS) is a group of inherited keratinopathies that, in most cases, arise due to mutations in keratins and lead to intraepidermal ruptures. The cellular pathology of most EBS subtypes is associated with the fragility of the intermediate filament network, cytolysis of the basal layer of the epidermis, or attenuation of hemidesmosomal/desmosomal components. Mutations in keratins 5/14 or in other genes that encode associated proteins induce structural disarrangements of different strengths depending on their locations in the genes. Keratin aggregates display impaired dynamics of assembly and diminished solubility and appear to be the trigger for endoplasmic reticulum (ER) stress upon being phosphorylated by MAPKs. Global changes in cellular signaling mainly occur in cases of severe dominant EBS mutations. The spectrum of changes initiated by phosphorylation includes the inhibition of proteasome degradation, TNF-α signaling activation, deregulated proliferation, abnormal cell migration, and impaired adherence of keratinocytes. ER stress also leads to the release of proinflammatory danger-associated molecular pattern (DAMP) molecules, which enhance avalanche-like inflammation. Many instances of positive feedback in the course of cellular stress and the development of sterile inflammation led to systemic chronic inflammation in EBS. This highlights the role of keratin in the maintenance of epidermal and immune homeostasis.

Cytokeratin 5 and cytokeratin 6 expressions are unconnected in normal and cancerous tissues and have separate diagnostic implications

Cytokeratins (CKs) 5 and 6 are functionally unrelated but often analyzed together using bispecific antibodies in diagnostic immunohistochemistry. To better understand the diagnostic utility of CK5 or CK6 alone, tissue microarrays with > 15,000 samples from 120 different tumor types as well as 608 samples of 76 different normal tissues were analyzed by immunohistochemistry. In normal tissues, both CKs occurred in the squamous epithelium; CK5 dominated in basal and CK6 in suprabasal layers. CK5 (not CK6) stained basal cells in various other organs. Within tumors, both CK5 and CK6 were seen in > 95% of squamous cell carcinomas, but other tumor entities showed different results: CK5 predominated in urothelial carcinoma and mesothelioma, but CK6 in adenocarcinomas. Joint analysis of both CK5 and CK6 obscured the discrimination of epithelioid mesothelioma (100% positive for CK5 alone and for CK5/6) from adenocarcinoma of the lung (12.8% positive for CK5 alone; 23.7% positive for CK5/6). CK5 and CK6 expressions were both linked to high grade, estrogen receptor, and progesterone receptor negativity in breast cancer (p < 0.0001 each), grade/stage progression in urothelial cancer (p < 0.0001), and RAS mutations in colorectal cancer (p < 0.01). Useful diagnostic properties which are commonly attributed to CK5/6 antibodies such as basal cell staining in the prostate, distinction of adenocarcinoma of the lung from squamous cell carcinoma and epithelioid mesothelioma, and identification of basal-type features in urothelial cancer are solely driven by CK5. At least for the purpose of distinguishing thoracic tumors, monospecific CK5 antibodies may be better suited than bispecific CK5/6 antibodies.

An updated classification of hair follicle morphogenesis

Hair follicle (HF) formation in developing embryonic skin requires stepwise signalling between the epithelial epidermis and mesenchymal dermis, and their specialized derivatives, the placode/germ/peg and dermal condensate/papilla, respectively. Classically, distinct stages of HF morphogenesis have been defined, in the mouse model, based on (a) changes in cell morphology and aggregation; (b) expression of few known molecular markers; (c) the extent of follicle downgrowth; and (d) the presence of differentiating cell types. Refined genetic strategies and recent emerging technologies, such as live imaging and transcriptome analyses of isolated cell populations or single cells, have enabled a closer dissection of the signalling requirements at different stages of HF formation, particularly early on. They have also led to the discovery of precursor cells for placode, dermal condensate and future bulge stem cells that, combined with molecular insights into their fate specification and subsequent formation, serve as novel landmarks for early HF morphogenetic events and studies of the signalling networks mediating these processes. In this review, we integrate the emergence of HF precursor cell states and novel molecular markers of fate and formation to update the widely used 20-year-old seminal classification guide of HF morphogenetic stages by Paus et al. We then temporally describe the latest insights into the early cellular and molecular events and signalling requirements for HF morphogenesis in relation to one another in a holistic manner.

Cellular organization and histogenesis of adenosquamous carcinoma of the pancreas: evidence supporting the squamous metaplasia concept

Adenosquamous carcinoma of the pancreas (ASCAP) is characterized by conventional pancreatic ductal adenocarcinoma (PDAC) and squamous carcinoma components with at least 30% of the tumour showing squamous differentiation. To get further insight into the histogenesis of these lesions, we analysed the cellular organization of ASCAP compared to PDACs. Using Immunohistochemistry and triple immunofluorescence labelling studies for keratins, p63, p40, MUC1, MUC2, MUC5AC, Ki67, and EGFR we demonstrate that many ASCAPs contain a transitional zone between the K8/18-positive adenocarcinomatous component and the p63+ /p40+ /K5/K14+ squamous component initiated by the expression of p63 in K8/18+ adenocarcinomatous cells and the appearance of basally located p63+ K5/14+ cells. p63+ K5/14+ cells give rise to fully developed squamous differentiation. Notably, 25% of conventional PDACs without histologically recognizable squamous component contain foci of p63+ p40+ and K5/14+ cells similar to the transitional zone. Our data provide evidence that the squamous carcinoma components of ASCAPs originate from pre-existing PDAC via transdifferentiation of keratin K8/18-positive glandular cells to p63-, p40-, and keratin K5/14-positive squamous carcinoma cells supporting the squamous metaplasia hypothesis. Thus our findings provide new evidence about the cellular process behind squamous differentiation in ASCAPs.

K-Ras and cyclooxygenase-2 coactivation augments intraductal papillary mucinous neoplasm and Notch1 mimicking human pancreas lesions

Mutational activation of K-Ras is an initiating event of pancreatic ductal adenocarcinomas (PDAC) that may develop either from pancreatic intraepithelial neoplasia (PanIN) or intraductal papillary mucinous neoplasms (IPMN). Cyclooxygenase-2 (COX-2)-derived prostaglandin E₂ (PGE₂) is causally related to pancreatic carcinogenesis. Here, we deciphered the impact of COX-2, a key modulator of inflammation, in concert with active mutant K-Ras^G12D on tumor burden and gene expression signature using compound mutant mouse lines. Concomitant activation of COX-2 and K-Ras^G12D accelerated the progression of pancreatic intraepithelial lesions predominantly with a cystic papillary phenotype resembling human IPMN. Transcriptomes derived from laser capture microdissected preneoplastic lesions of single and compound mutants revealed a signature that was significantly enriched in Notch1 signaling components. In vitro, Notch1 signaling was COX-2-dependent. In line with these findings, human IPMN stratified into intestinal, gastric and pancreatobillary types displayed Notch1 immunosignals with high prevalence, especially in the gastric lesions. In conclusion, a yet unknown link between activated Ras, protumorigenic COX-2 and Notch1 in IPMN onset was unraveled.

SuperSILAC Quantitative Proteome Profiling of Murine Middle Ear Epithelial Cell Remodeling with NTHi

Background

Chronic Otitis Media with effusion (COME) develops after sustained inflammation and is characterized by secretory middle ear epithelial metaplasia and effusion, most frequently mucoid. Non-typeable Haemophilus influenzae (NTHi), the most common acute Otitis Media (OM) pathogen, is postulated to promote middle ear epithelial remodeling in the progression of OM from acute to chronic. The goals of this study were to examine histopathological and quantitative proteomic epithelial effects of NTHi challenge in a murine middle ear epithelial cell line.

Methods

NTHi lysates were generated and used to stimulate murine epithelial cells (mMEEC) cultured at air-liquid interface over 48 hours– 1 week. Conditional quantitative Stable Isotope Labeling with Amino Acids in Cell Culture (SILAC) of cell lysates was performed to interrogate the global protein production in the cells, using the SuperSILAC technique. Histology of the epithelium over time was done to measure bacterial dependent remodeling.

Results

Mass spectrometry analysis identified 2,565 proteins across samples, of which 74 exhibited differential enrichment or depletion in cell lysates (+/-2.0 fold-change; p value<0.05). The key molecular functions regulated by NTHi lysates exposure were related to cell proliferation, death, migration, adhesion and inflammation. Finally, chronic exposure induced significant epithelial thickening of cells grown at air liquid interface.

Conclusions

NTHi lysates drive pathways responsible of cell remodeling in murine middle ear epithelium which likely contributes to observed epithelial hyperplasia in vitro. Further elucidation of these mediators will be critical in understanding the progression of OM from acute to chronic at the molecular level.

Assays to Study Consequences of Cytoplasmic Intermediate Filament Mutations: The Case of Epidermal Keratins

The discovery of the causative link between keratin mutations and a growing number of human diseases opened the way for a better understanding of the function of the whole intermediate filament families of cytoskeleton proteins. This chapter describes analytical approaches to identification and interpretation of the consequences of keratin mutations, from the clinical and diagnostic level to cells in tissue culture. Intermediate filament pathologies can be accurately diagnosed from skin biopsies and DNA samples. The Human Intermediate Filament Database collates reported mutations in intermediate filament genes and their diseases, and can help clinicians to establish accurate diagnoses, leading to disease stratification for genetic counseling, optimal care delivery, and future mutation-aligned new therapies. Looking at the best-studied keratinopathy, epidermolysis bullosa simplex, the generation of cell lines mimicking keratinopathies is described, in which tagged mutant keratins facilitate live-cell imaging to make use of today's powerful enhanced light microscopy modalities. Cell stress assays such as cell spreading and cell migration in scratch wound assays can interrogate the consequences of the compromised cytoskeletal network. Application of extrinsic stresses, such as heat, osmotic, or mechanical stress, can enhance the differentiation of mutant keratin cells from wild-type cells. To bring the experiments to the next level, 3D organotypic human cultures can be generated, and even grafted onto the backs of immunodeficient mice for greater in vivo relevance. While development of these assays has focused on mutant K5/K14 cells, the approaches are often applicable to mutations in other intermediate filaments, reinforcing fundamental commonalities in spite of diverse clinical pathologies.

Pathology analysis for mesothelioma study in the United Kingdom: Current practice and historical development

Following up on the largest case-control study of malignant mesothelioma yet performed, investigators at the London School of Hygiene and Tropical Medicine assessed 1732 male and 670 female cases as of May 2013. Epidemiological findings of a subset of these were published previously, excluding patients who died or who refused to be interviewed. Pathology reports were collected for subjects, including those both eligible and ineligible for epidemiology study based on vital status. The current investigation examined 860 cases having pathology reports available. Sixty-one cases were diagnosed using cytology only, often with equivocal diagnoses, while 799 reported at least a biopsy of the tumor. Of these, 748 had pathology sufficiently detailed for evaluation. These reports were examined for basis of diagnosis, differences between study cases and ineligible cases, pathology characteristics, and immunohistochemical and other tests used. The most prominent subtype was epithelioid (64% of study cases but only 49% of ineligible cases). Biphasic subtype was present in 10% of study cases and 16% of those ineligible. Sarcomatoid subtype was present in 7% of study cases and 19% of ineligible cases, most of whom died. Twelve percent of study cases displayed no specified subtype, versus 7% of ineligible cases. Of recorded immunohistochemical stains specific for mesothelial cell origin, calretinin (95%) and CK 5/6 or CK5 alone (84%) were by far the most common. Calretinin and CK 5/6 or CK 5 alone were also most sensitive and positive in 92% of cases presenting with surgical pathology report. Ninety percent of cases had at least one immunohistochemical marker for possible lung carcinoma applied, with BER-Ep4 and TTF-1 the most frequent at 68% and CEA at 58%. TTF-1 and CEA were positive in 1% or less of cases. Patterns of use and positive and negative results for each of these as well as other immunohistochemical stains are presented and discussed, along with a brief historical description of their development and use. Possible effects of the pathologic analysis on the results of previously published and future epidemiological studies are discussed.

Proteomic profile of keratins in cancer of the gingivo buccal complex: consolidating insights for clinical applications

Keratins play a major role in several cellular functions. Each tissue type expresses a specific set of keratins. The immense potential of keratins as diagnostic and prognostic markers for different cancers is emerging. Oral cancer is the fifteenth most common cancer worldwide. However, comprehensive information on the profile of keratins in the oral cavity is not available. Several independent reports have identified keratins using antibody based techniques which have pitfalls due to the cross reactivity of the antibodies to this set of very homologous proteins. A few recent proteomic studies have reported the identification of keratins in head and neck cancer. Majority of the studies have used tissues from the head and neck region without specifying subsites. This study reports the analysis of enriched preparations of keratins from cancer of the gingivo buccal complex (GBC) using MS, 2DE, WB, silver staining of 2DE gels and IHC. Our study reveals the absence of K4 and K13 and presence of K14, K16, and K17, in cancers of the GBC and combination of these expression patterns in the cut margins. This report also shows that K13 is glycosylated. This well characterized profile of keratins may have potential to be used in clinics.

BIOLOGICAL SIGNIFICANCE

In recent years the immense potential of keratins as diagnostic and prognostic markers for different cancers is emerging. However, comprehensive information on the profile of keratins in the oral cavity is not available. Several independent reports have identified keratins using only antibody based techniques which have pitfalls due to the cross reactivity of the antibodies to this set of very homologous proteins. This study reports the analysis of enriched preparations of keratins from a subsite of the oral cavity, the gingivo buccal complex (GBC) using mass spectrometry, 2DE, western blotting, silver staining of 2DE gels and IHC. The proteomic analysis shows the absence of K4 and K13 and presence of K14, K16, and K17 in cancers of the GBC and combination of these expression patterns in the cut margins. This well characterized profile of keratins from the gingivo buccal complex provides defined markers which may have potential to be used in the clinics.

Contribution of proteomics to the study of the role of cytokeratins in disease and physiopathology

Cytokeratins (CKs), the most abundant group of cytoskeletal intermediate filaments, and proteomics are strongly connected. On the one hand, proteomics has been extremely useful to uncover new features and functions of CKs, on the other, the highly abundant CKs serve as an exceptional tool to test new technological developments in proteomics. As a result, proteomics has contributed to finding valuable associations of CKs with diseases as diverse as cancer, cystic fibrosis, steatohepatitis, viral and bacterial infection, keratoconus, vitreoretinopathy, preeclampsia or the chronic fatigue syndrome, as well as to characterizing their participation in a number of physiopathological processes, including drug resistance, response to toxicants, inflammation, stem cell differentiation, embryo development, and tissue repair. In some cases, like in cystic fibrosis, CKs have been described as potential therapeutic targets. The development of a specific field of proteomics where CKs become the main subject of research aims and hypotheses is suggested.

Spatiotemporal regulation of keratin 5 and 17 in the axolotl limb

BACKGROUND

Amphibians have greater regeneration capability than higher vertebrates. They can regenerate their limbs after an amputation. As a limb is regenerated, a regeneration-specific epithelium called the apical epithelial cap (AEC) is induced. The AEC is an essential structure for limb regeneration. Despite the importance of the AEC, molecular marker genes have not been well studied at the molecular level.

RESULTS

In the present study, keratin5 (KRT5) and KRT17 were investigated in an axolotl-regenerating limb. KRT5 and KRT17 were expressed in a regenerating limb but down-regulated in a differentiating limb. KRT5 showed characteristic regulation in a regenerating blastema. KRT5 was suppressed in the basal layer of the AEC. This KRT5 suppression was correlated to the blastema differentiation and nerve presence. Simple skin wounding could also upregulate both KRT5 and KRT17 gene expression. But these genes were suppressed within a shorter time than in limb regeneration.

CONCLUSIONS

The KRT5 and KRT17 gene profile can be a useful marker gene to investigate AEC in limb regeneration.

Novel function of keratins 5 and 14 in proliferation and differentiation of stratified epithelial cells

Keratin expression in stratified epithelia is tightly regulated during squamous cell differentiation. Keratins 5 and 14 are expressed in mitotically active basal layer cells, but their function is not well defined. Reported here is the possible role of K14 in regulation of cell proliferation/differentiation in stratified epithelial cells.

Keratins are cytoplasmic intermediate filament proteins preferentially expressed by epithelial tissues in a site-specific and differentiation-dependent manner. The complex network of keratin filaments in stratified epithelia is tightly regulated during squamous cell differentiation. Keratin 14 (K14) is expressed in mitotically active basal layer cells, along with its partner keratin 5 (K5), and their expression is down-regulated as cells differentiate. Apart from the cytoprotective functions of K14, very little is known about K14 regulatory functions, since the K14 knockout mice show postnatal lethality. In this study, K14 expression was inhibited using RNA interference in cell lines derived from stratified epithelia to study the K14 functions in epithelial homeostasis. The K14 knockdown clones demonstrated substantial decreases in the levels of the K14 partner K5. These cells showed reduction in cell proliferation and delay in cell cycle progression, along with decreased phosphorylated Akt levels. K14 knockdown cells also exhibited enhanced levels of activated Notch1, involucrin, and K1. In addition, K14 knockdown AW13516 cells showed significant reduction in tumorigenicity. Our results suggest that K5 and K14 may have a role in maintenance of cell proliferation potential in the basal layer of stratified epithelia, modulating phosphatidylinositol 3-kinase/Akt–mediated cell proliferation and/or Notch1-dependent cell differentiation.

The human keratins: biology and pathology

The keratins are the typical intermediate filament proteins of epithelia, showing an outstanding degree of molecular diversity. Heteropolymeric filaments are formed by pairing of type I and type II molecules. In humans 54 functional keratin genes exist. They are expressed in highly specific patterns related to the epithelial type and stage of cellular differentiation. About half of all keratins—including numerous keratins characterized only recently—are restricted to the various compartments of hair follicles. As part of the epithelial cytoskeleton, keratins are important for the mechanical stability and integrity of epithelial cells and tissues. Moreover, some keratins also have regulatory functions and are involved in intracellular signaling pathways, e.g. protection from stress, wound healing, and apoptosis. Applying the new consensus nomenclature, this article summarizes, for all human keratins, their cell type and tissue distribution and their functional significance in relation to transgenic mouse models and human hereditary keratin diseases. Furthermore, since keratins also exhibit characteristic expression patterns in human tumors, several of them (notably K5, K7, K8/K18, K19, and K20) have great importance in immunohistochemical tumor diagnosis of carcinomas, in particular of unclear metastases and in precise classification and subtyping. Future research might open further fields of clinical application for this remarkable protein family.

Expression of keratin 14 in the basal cells of the lingual epithelium of mice during the morphogenesis of filiform papillae: visualization by fluorescent immunostaining and confocal laser-scanning microscopy in the transmission mode

We examined the expression of keratin 14 (K14) on the lingual epithelium by immunofluorescent staining while monitoring morphological changes in the filiform papillae of mice by confocal laser-scanning microscopy in the transmission mode of the same sections to define both the histology and the morphology of cells. It is difficult to visualize histological details of the fetal lingual epithelium of the mouse on semi-ultrathin sections by light microscopy after immunohistochemical staining because the histological structures in such sections cannot be distinguished by standard counterstaining. To solve this problem and to visualize the immunoreactivity specific for K14, we analyzed the results of immunofluorescent staining of semi-ultrathin sections in combination with an examination of the corresponding images by laser-scanning microscopy in the transmission mode after staining of specimens with toluidine blue. No immunoreactivity specific for K14 was detected on the lingual epithelium of fetuses on embryonic day 15 (E15), but immunoreactivity was distinct at all postnatal stages from postnatal day 0 (P0) to P21.

Immunohistochemical marker panels for distinguishing between epithelioid mesothelioma and lung adenocarcinoma

The distinction between epithelioid mesothelioma and lung adenocarcinoma remains an important diagnostic challenge for surgical pathologists. The aim of the present study was to select a limited and appropriate panel of antibodies that can differentiate between epithelioid mesothelioma and lung adenocarcinoma. Specimens of 90 epithelioid mesotheliomas and 51 lung adenocarcinomas obtained from Japanese cases were examined using calretinin, WT1, AE1/AE3, CAM5.2, cytokeratin (CK) 5/6, vimentin, epithelial membrane antigen (EMA), thrombomodulin, CEA, CA19-9, and CA125. Ninety-six percent of epithelioid mesotheliomas were positive for calretinin; 99% for WT1; 100% for AE1/AE; 97% for CAM5.2; 70% for CK 5/6; 91% for vimentin; 96% for EMA; 71% for thrombomodulin; 77% for mesothelin; 7% for CEA; 17% for CA19-9; and 85% for CA125. In contrast, 33% of lung adenocarcinomas were positive for calretinin; 16% for WT1; 100% for AE1/AE3, CAM5.2, and EMA; 41% for CK 5/6; 47% for vimentin; 20% for thrombomodulin; 69% for mesothelin; 98% for CEA; 73% for CA19-9; and 80% for CA125. For distinguishing between epithelioid mesothelioma and lung adenocarcinoma, the combination of CEA, calretinin and each WT1 or thrombomodulin was suggested to be the best panel of immunohistochemical markers.

Applications and limitations of immunohistochemistry in the diagnosis of malignant mesothelioma

Malignant mesothelioma is an uncommon malignant epithelial neoplasm originating from the serosal surface of body cavities. Because serosal surfaces are a common site of metastatic spread for a variety of malignant neoplasms originating from internal organs, separating malignant mesothelioma from metastatic tumors is of clinical importance. The diagnosis of malignant mesothelioma is complex and usually requires a multimodal approach that includes careful clinical history and physical examination, imaging studies, and tissue sampling for multimodal evaluation including routine histology, histochemistry, electron microscopy, and immunohistochemical tests. Of these, immunohistochemistry has emerged as the most valuable and readily available modality for the routine evaluation of these tumors. Unfortunately, no specific antibodies have yet been developed that can be accepted as exclusive for these tumors. The immunohistochemical diagnosis of malignant mesothelioma therefore depends on the use of a panel of stains that includes markers that are commonly expected to react with these tumors ("positive" markers) and markers that are not commonly expected to react with these tumors ("negative" markers). Additionally, the selection and utility of these various markers can vary considerably based on a constellation of circumstances, including patient sex, histologic appearance of the tumor (ie, epithelioid vs. sarcomatoid, etc), and various other clinical circumstances. Herein, we will review the currently available immunohistochemical markers used for the diagnosis of malignant mesothelioma and offer suggestions for the use of appropriate panels of stains based on specific morphologic types and clinical circumstances.

Expression of renal cell carcinoma-associated markers erythropoietin, CD10, and renal cell carcinoma marker in diffuse malignant mesothelioma and metastatic renal cell carcinoma

CONTEXT

Metastatic renal cell carcinoma (MRCC) involving the thorax can be difficult to distinguish from diffuse malignant mesothelioma (DMM) using traditional morphologic approaches. Standard panels of immunohistochemical markers are of limited benefit.

OBJECTIVE

To investigate several antibodies to renal cell carcinoma-associated proteins for differentiating MRCC from DMM.

DESIGN

One hundred DMMs and 20 MRCCs were evaluated for immunoexpression of erythropoietin. The same cases and an additional 45 DMMs were evaluated for CD10 and renal cell carcinoma marker (RCCMa) immunoreactivity.

RESULTS

Erythropoietin was expressed in 100% of DMMs and MRCCs. Staining for CD10 was observed in 54% of DMMs and 100% of MRCCs. RCCMa stained 26% of DMMs and 55% of MRCCs. Although erythropoietin staining was similarly strong and diffuse in both DMM and MRC, patterns of staining for RCCMa and CD10 differed between MRCC and DMM. Immunoreactivity was strong and diffuse for both RCCMa and CD10 in most MRCCs. Of CD10-positive DMMs, nearly half showed staining in less than 50% of tumor cells and about one fourth of positive cases exhibited only weak to moderately intense staining. Only half of RCCMa-positive DMMs showed staining in more than 49% of tumor cells and staining was only weak to moderately intense in most cases.

CONCLUSIONS

Given the overlap in the expression of renal cell carcinoma markers in MRCC and DMM, results with these markers must be interpreted cautiously and should be used in conjunction with mesothelium-associated markers. Differences in expression may potentially help distinguish MRCC from DMM inasmuch as strong and diffuse expression of RCCMa and CD10 supports a diagnosis of MRCC over DMM.

Preinvasive duct-derived neoplasms in pancreas of keratin 5-promoter cyclooxygenase-2 transgenic mice

BACKGROUND & AIMS

Basic research aimed at a better understanding of pancreatic carcinogenesis and improving the treatment of this disease is crucial because the majority of pancreatic cancers are highly aggressive and therapeutically nonaccessible. Cyclooxygenase (COX)-2, which is a key enzyme of prostaglandin (PG) biosynthesis, is overexpressed in around 75% of human carcinomas including those of the pancreas.

METHODS

The pathologic changes of transgenic mouse pancreas with keratin 5-promoter-driven expression and activity of COX-2 were characterized.

RESULTS

Aberrant expression of COX-2 in a few ductal cells and COX-2-mediated PG synthesis in the transgenic mice resulted in keratin 19- and mucin-positive intraductal papillary mucinous neoplasm- and pancreatic intraepithelial neoplasia-like structures, characterized by an increased proliferation index and serous cystadenomas. Moreover, Ras activation was enhanced and the HER-2/Neu receptor was overexpressed. Loss of acini, fibrosis, and inflammation were pronounced. Feeding a COX-2-selective inhibitor to the transgenic mice suppressed the accumulation of PG and the phenotype. The changes resemble the human disease in which COX-2 was overexpressed consistently.

CONCLUSIONS

We present strong evidence for a causal relationship between aberrant COX-2 overexpression and COX-2-mediated PG synthesis and the development of serous cystadenoma, intraductal papillary mucinous, and pancreatic intraepithelial neoplasms. This model offers the unique possibility of identifying molecular pathways leading to the formation and malignant progression of the various types of preinvasive lesions of pancreatic adenocarcinomas that show different dismal outcomes.

Cytokeratin expression in oral submucous fibrosis--an immunohistochemical study

BACKGROUND

Oral submucous fibrosis (OSF) is a pre-malignant condition caused by habitual use of areca nut, affecting the oro-pharynx and characterized by progressive fibrosis. Alteration of cytokeratin (CK) expression has been documented in leukoplakia and oral cancer (OC). However, very little is known of CK alterations in OSF. The present study was carried out to characterize the CK profile in OSF and ascertain if this could be used as a surrogate marker for malignant transformation.

METHODS

Paraffin-embedded tissues of OSF (n = 50), normal (n = 10) and OC (n = 10) were stained with pancytokeratin (PanCK), high molecular weight cytokeratin (HMWCK), CKs 18, 14, 8, 5, 4 and 1 by immunohistochemistry.

RESULTS

Significant difference in the CK staining pattern was seen between normal, OSF and cancer. Significant changes in OSF included increased intensity of staining for PanCK and HMWCK, aberrant expression of CK8 and decreased expression of CKs 5 and 14.

CONCLUSION

Cytokeratin profile of OSF was significantly different from normals for PanCK, HMWCK, CK8, 5 and 14 suggesting their potential to be used as surrogate markers of malignant transformation. Further studies will help in better defining the nature and clinical implications of these alterations.

Evaluation of 12 antibodies for distinguishing epithelioid mesothelioma from adenocarcinoma: identification of a three-antibody immunohistochemical panel with maximal sensitivity and specificity

We evaluated the sensitivity and specificity of 10 monoclonal and two polyclonal antibodies for distinguishing epithelioid mesothelioma from adenocarcinoma (AdCA) using immunohistochemistry (IHC). The antibodies were directed against the mesothelial-associated antigens mesothelin, calretinin, cytokeratin 5, thrombomodulin, Wilms' tumor-1 (WT-1) gene product and HBME-1, and the nonmesothelial antigens Lewis-Y blood group (antibody BG8), MOC-31, BerEp4, CD15, and carcinoembryonic antigen (CEA) family. The 133 tumors evaluated included 65 malignant epithelioid mesotheliomas, 22 lung AdCAs, 27 ovarian serous carcinomas, 24 breast carcinomas, and five gastric carcinomas. Diagnoses were based on clinical, histologic, ultrastructural, and/or IHC findings. Calretinin had the best sensitivity for mesothelioma (95%), followed by HBME-1 (84%), WT-1 (78%), cytokeratin 5 (76%), mesothelin (75%), and vimentin and thrombomodulin (68%). Thrombomodulin had the best specificity for mesothelioma (92%), followed by cytokeratin 5 (89%), calretinin (87%) vimentin (84%), and HBME-1 (45%). When ovarian carcinomas were excluded from the analysis, the specificity of mesothelin and WT-1 for the diagnosis of mesothelioma increased to 90 and 81%, respectively. The sensitivity of the nonmesothelial antigens for AdCA was organ dependent, with BG8 performing best in the breast cancer group (96%), and BerEp4, BG8, MOC-31 performing best in the lung cancer group (100%). The specificity of the nonmesothelial antigens for AdCA was 98% for BG8 and CEA, 97% for CD15, 95% for BerEp4, and 87% for MOC-31. A novel statistical analysis technique employing logic regression analysis identified a three-antibody immunohistochemical panel including calretinin, BG8, and MOC-31, which provided over 96% sensitivity and specificity for distinguishing epithelioid mesothelioma from AdCA.

Establishment and characterization of murine small cell lung carcinoma cell lines derived from HPV-16 E6/E7 transgenic mice

We have established two murine cell lines derived from Small Cell Lung Carcinomas (SCLCs) developed by HPV-E6/E7 transgenic mice. These cells named PPAP-9 and PPAP-10 were isolated from mice bearing tumors, 9 and 10 months old, respectively. The cells, 5 microm in diameter, express HPV oncoproteins and sustain tumor formation after subcutaneous injection in syngenic mice. A detailed analysis indicated the epithelial origin and the neuroendocrine differentiation of these cells. We showed by confocal immunofluorescence the expression of the epithelial marker cytokeratin 5, whose gene promoter was used to direct the expression of HPV E6/E. Cells express several neuroendocrine markers such as CGRP, MAP-2, Ash1, CgrA, Scg2. The neuroendocrine differentiation of these cells was further confirmed by electron microscopy demonstrating neuropeptides secreting granules in their cytoplasm. Furthermore, in agreement with the altered expression observed in the majority of human SCLC we showed in these cells the absence of both p53 and pRB and a dramatic reduction in the expression of Caveolin-1.

Immunohistochemical expression of keratins 13 and 14 in the lingual epithelium of rats during the morphogenesis of filiform papillae

We examined the immunofluorescence of keratins 13 (K13) and 14 (K14) and differential interference contrast (DIC) images during the morphogenesis of filiform papillae and the keratinization of the lingual epithelium of rats on semi-ultrathin sections of epoxy resin-embedded samples by laser-scanning microscopy. We also examined semi-ultrathin sections of epoxy resin embedded, toluidine blue stained samples by light microscopy to obtain details of cell histology and morphology. No immunoreactivity specific for K13 and K14 was detected on the lingual epithelium of foetuses on days 13, 15 and 17 after conception (E13, E15 and E17), during which time the number of layers of cuboidal cells in the lingual epithelium increased from one to several. Immunoreactivity specific for K13 and K14 was first detected on the lingual epithelium of foetuses on E19. The immunoreactivity specific for K13 appeared in the suprabasal cells of the papillary and interpapillary cell columns and immunoreactivity specific for K14 was detected in the basal and suprabasal cells of the papillary and interpapillary cell columns. The lingual epithelium was composed of stratified squamous cells. The rudiments of filiform papillae were compactly arranged and interpapillary cell columns were very narrow. Filiform papillae developed gradually from postnatal day 0 (PO) to 21 (P21). The width of interpapillary spaces also increased during this period. Immunoreactivity specific for K13 and K14 was distinct at all postnatal stages examined. Thus, the patterns of immunoreactivity of K13 and K14 differed as the filiform papillae developed.

Malignant pleural mesothelioma

Malignant pleural mesothelioma is an uncommon tumor; only about 3000 cases are diagnosed annually in the United States. Cases were described early in the 20th century, but their relationship to asbestos exposure was not documented until 1960. Since then, the incidence has appeared to increase, and numerous epidemiologic studies have confirmed that exposure to asbestos in a variety of settings and occupations is the most significant risk factor for the development of malignant pleural mesothelioma. More recently, the oncogenic virus SV40 has also been implicated as a potential etiologic agent. Surgery, radiotherapy, and chemotherapy have each been used in the treatment of mesothelioma, but generally with little impact on survival. New directions in therapy include aggressive multimodality programs for potentially resectable patients and targeted therapies, including antifolates, antiangiogenesis agents, and drugs directed at epidermal growth factor receptor for the majority of patients presenting with unresectable disease.

Immunocytochemical identification of carcinomas of unknown primary in serous effusions

Metastases from carcinomas of unknown primary site (CUP) in serous effusion are a common clinical problem. Immunocytochemistry was applied as an adjunct to the cytological diagnosis of metastatic carcinomas in serous effusions. Subjects of this study were 118 pleural, 53 peritoneal, and 9 pericardial effusions from 180 patients routinely investigated in the Institute of Cytopathology. Specimens were primarily stained according to Papanicolaou (Pap). The avidin-biotin-complex method (ABC) was secondarily applied for the visualization of immunologic reactions. We have used a panel of six monoclonal antibodies (CK 5/6, CK 7, CK 20, CA 125, TTF-1, and cdx 2) so as to identify the primary tumor site of metastatic carcinoma cells in serous effusions. Applying an algorithm of immunocytochemical marker constellations, we were able to correctly diagnose primary tumor sites in 86 of 101 (85.1%) patients with CUP syndromes. The best result was achieved for the identification of metastatic carcinomas of the ovaries (94.7%) and the lungs (88.1%). We established an algorithm comprising six immunocytochemical markers that enabled a correct diagnosis of primary tumor sites in 85.1%. The panel studied could be useful in diagnostic routine for the identification of primary tumors of unknown origin metastatic to the serous membranes.

Histopathologic classification of lung cancer: Relevance of cytokeratin and TTF-1 immunophenotyping

Histopathologic classification of lung carcinoma is important, as a prognostic factor and in the evaluation of treatment modalities. Although the World Health Organization classification of lung cancer is based on routine microscopy, immunohistochemistry is an important additional aspect in modern pathologic practice. This study examines whether the main histologic types of lung carcinomas are more reliably diagnosed with immunohistochemical technique using antibodies for the lung tissue-specific antigen thyroid transcription factor-1 (TTF-1) and a panel of cytokeratin (CK) antibodies. Forty-five cases of lung cancer (12 squamous cell carcinoma, 13 small cell carcinoma, 11 adenocarcinoma, 9 large cell carcinoma [LCC]/pleomorphic carcinoma) were stained with antibodies to CK CAM5.2, CK5, CK7, CK20, and TTF-1. All 45 cases were positive with CAM5.2, 16 of 45 cases with CK5, 34 of 45 cases with CK7, 4 of 45 cases with CK20, and 29 of 45 with TTF-1. Squamous cell carcinoma (epidermoid carcinoma) had the immunophenotype CK5+/TTF-1-, and at least 20% were also positive with CK7. Most nonepidermoid tumors had the "lung-specific" phenotype CK5-/TTF-1+; all small cell carcinomas had the phenotype CK5-/CK8+/TTF-1+, all adenocarcinomas CK5-/CK7+/TTF-1+ and (more than 50%) of LCC CK5-/CK7+/TTF-1+. Thus, more than 50% of LCCs were of the same phenotype as adenocarcinomas. The immunophenotypes of the main histologic types of lung carcinoma are stable and highly reproducible. However, because of considerable overlapping, immunophenotyping should not be used alone for histopathologic classification of lung cancer, but only as an adjunct to light microscopy. It is also suggested that CK5+ lung carcinomas with basaloid features should be regarded as variants of squamous cell carcinoma and not as LCC.

‘Pseudomesotheliomatous’ carcinomas of the pleura: a 10-year analysis of cases from the Environmental Lung Disease Research Group, Cardiff

AIMS

To undertake a clinicopathological study of diffuse serosal neoplasms of epithelial histogenesis which clinically and pathologically mimic malignant pleural mesothelioma.

METHODS AND RESULTS

Over a 10-year (1990-2000) study period 53 carcinomas mimicking diffuse pleural mesothelioma ('pseudomesotheliomatous' carcinoma) were identified. The study group comprised 50 men and three females, age range 33-77 (median 68) years. In 46 (87%) cases there was a history of smoking and in 40 (76%) cases a history of asbestos exposure. Histologically the pleural 'pseudomesotheliomatous' carcinomas could be divided into two broad groups: primary pulmonary carcinomas with florid pleurotropic growth (n = 47), of which 34 (70%) were adenocarcinomas; and diffuse carcinomatous involvement of the pleura by metastatic tumour (n = 6). This latter group comprised two transitional cell carcinomas of bladder, one renal (clear) cell carcinoma, one ductal pancreatic adenocarcinoma, one prostatic adenocarcinoma and one squamous cell carcinoma of parotid gland origin. Follow-up data were available in 35 cases. Regardless of tumour type, survival was poor (median 8 months) and comparable to diffuse pleural mesothelioma.

CONCLUSIONS

Pleural 'pseudomesotheliomatous' carcinomas are uncommon (comprising 6% of referrals), pathologically heterogeneous tumours with poor prognosis. Tissue diagnosis should be obtained in all cases of suspected diffuse pleural neoplasia. By light microscopy and immunophenotype many of the tumours mimicked malignant mesothelioma. In particular, an awareness that all neoplasms exhibiting squamous differentiation may express cytokeratin 5/6 and thrombomodulin is important to prevent misinterpretation. In this respect, calretinin is regarded as the most specific and sensitive mesothelial marker. Misdiagnosis may have medico-legal implications in asbestos-related compensation claims.

The immunohistochemical diagnosis of mesothelioma: a comparative study of epithelioid mesothelioma and lung adenocarcinoma

A large number of immunohistochemical markers that can facilitate the distinction between epithelioid pleural mesotheliomas and pulmonary peripheral adenocarcinomas have recently become available. The aim of this study is to compare the value of these new markers with others that are already commonly used for this purpose and to determine which are, at present, the best for discriminating between these malignancies. Sixty epithelioid mesotheliomas and 50 lung adenocarcinomas were investigated for expression of the following markers: calretinin, cytokeratin 5/6, WT1, thrombomodulin, mesothelin, CD44S, HBME-1, N-cadherin, E-cadherin, MOC-31, thyroid transcription factor-1 (TTF-1), BG-8 (Lewisy), carcinoembryonic antigen (CEA), Ber-EP4, B72.3 (TAG-72), leu-M1 (CD15), CA19-9, epithelial membrane antigen (EMA), and vimentin. All (100%) of the mesotheliomas reacted for calretinin, cytokeratin 5/6, and mesothelin, 93% for WT1, 93% for EMA, 85% for HBME-1, 77% for thrombomodulin; 73% for CD44S, 73% for N-cadherin, 55% for vimentin, 40% for E-cadherin, 18% for Ber-EP4, 8% for MOC-31, 7% for BG-8, and none for CEA, B72.3, leu-M1, TTF-1, or CA19-9. Of the adenocarcinomas, 100% were positive for MOC-31, Ber-EP4, and EMA, 96% for BG-8, 88% for CEA, 88% for E-cadherin, 84% for B72.3, 74% for TTF-1, 72% for leu-M1, 68% for HBME-1, 48% for CD44S, 48% for CA19-9, 38% for mesothelin, 38% for vimentin, 30% for N-cadherin, 14% for thrombomodulin, 8% for calretinin, 2% for cytokeratin 5/6, and none for WT1. After analyzing the results, it is concluded that calretinin, cytokeratin 5/6, and WT1 are the best positive markers for differentiating epithelioid malignant mesothelioma from pulmonary adenocarcinoma. The best discriminators among the antibodies considered to be negative markers for mesothelioma are CEA, MOC-31, Ber-EP4, BG-8, and B72.3. A panel of four markers (two positive and two negative) selected based upon availability and which ones yield good staining results in a given laboratory is recommended. Because of their specificity and sensitivity for mesotheliomas, the best combination appears to be calretinin and cytokeratin 5/6 (or WT1) for the positive markers and CEA and MOC-31 (or B72.3, Ber-EP4, or BG-8) for the negative markers. An extensive and detailed review of the literature is also provided.

Immunohistochemical detection of the expression of keratin 14 in the lingual epithelium of rats during the morphogenesis of filiform papillae

An immunofluorescence study of the expression of keratin 14 (K14) during the formation of filiform papillae was performed and the progress of keratinization of the epithelium of the rat tongue was monitored on semi-ultrathin sections by laser-scanning microscopy. Differential interference contrast (DIC) images were also examined to provide details of histology and cell morphology. No cells with immunoreactivity specific for K14 were detected on the lingual epithelium of foetuses on embryonic days 12 and 16 (E12 and E16), when the lingual epithelium was composed of a single layer or several layers of cuboidal cells. Immunoreactivity specific for K14 was detected first on basal and suprabasal keratinocytes of the dorsal epithelium of the tongue of new-borns on postnatal day 0 (P0) and was conspicuous in juveniles on P14. The immunoreactivity was particularly strong on the basal and suprabasal keratinocytes along the connective tissue papillae. The immunoreactivity extended over the entire cytoplasm but was not detected in the nucleus. The lingual epithelium was composed of stratified squamous cells and the rounded rudiments of filiform papillae were compactly arranged at equal intervals, for the most part, and the spaces between them were narrow and indistinct. Immunostaining of K14 was distinct on basal and suprabasal keratinocytes of the filiform papillar area of tongues of juveniles on P21, when the filiform papillae were conical. The spaces between them were relatively wide and, as a result, interpapillar cell columns were clearly visible. Immunoreactivity specific for K14 in the basal and suprabasal keratinocytes of the interpapillar cell columns was recognizable but was weaker than that in cells of papillar cell columns. The thickness of the epithelium in papillar and interpapillar areas increased gradually with the development of filiform papillae. However, sizes of basal and suprabasal keratinocytes remained almost unchanged during this process. These results suggest that the basal and suprabasal keratinocytes of the filiform papillar area proliferate with the initiation of the morphogenesis of filiform papillae and the keratinization of the epithelium. In addition, it appears that, after P14, the basal and suprabasal keratinocytes of the interpapillar area proliferate to supply the keratinocytes of the expanding interpapillar regions.

Epithelioid sarcoma: an immunohistochemical analysis evaluating the utility of cytokeratin 5/6 in distinguishing superficial epithelioid sarcoma from spindled squamous cell carcinoma

BACKGROUND

Epithelioid sarcoma (ES) is a rare, aggressive soft tissue tumor characterized by nodular aggregates of epithelioid and/or spindled cells that are immunoreactive to cytokeratins (CKs) and epithelial membrane antigen. ES that arises in the dermis may cause epidermal ulceration and can resemble, clinically, morphologically and immunohistochemically, cutaneous squamous cell carcinoma. CK 5/6 has recently been found to be an excellent marker of squamous cell carcinoma, including spindled variants, but it is not known if this marker can be utilized to distinguish superficial ES from cutaneous spindled squamous cell carcinoma (SSCC).

METHODS

Twenty-four cases of ES with typical histologic features and 10 cases of SSCC with ultrastructural evidence of epithelial differentiation were studied. Immunohistochemical analysis using an antibody to CK 5/6 was performed. The extent of immunoreactivity was evaluated in a semiquantitative manner using the following scale: 0, < 5% of cells staining; 1+, 6-25% of cells staining; 2+, 26-50% of cells staining; 3+, 51-75% of cells staining; 4+, > 75% of cells staining.

RESULTS

CK 5/6 was expressed in all 10 cases of SSCC, including one case with 3+ staining and six cases with 4+ staining. In contrast, CK 5/6 staining was found only in rare tumor cells (1+ staining) in one of 24 (4%) cases of ES.

CONCLUSIONS

CK 5/6 staining is useful in distinguishing superficial ES from cutaneous SSCC.

Expression of calretinin, thrombomodulin, keratin 5, and mesothelin in lung carcinomas of different types: an immunohistochemical analysis of 596 tumors in comparison with epithelioid mesotheliomas of the pleura

Several immunohistochemical markers, among them calretinin, thrombomodulin (CD141), keratin 5, and mesothelin, have been documented or suggested as useful markers for positive identification of mesothelioma and to differentiate it from pulmonary adenocarcinoma; numerous studies have documented their variable specificity. However, expression of these markers in other types of lung carcinomas has not been systematically explored, although these tumors can enter in the differential diagnosis of mesothelioma. In this study we immunohistochemically evaluated 596 lung carcinomas of different types for the four above-mentioned mesothelioma markers, all of which reacted with a great majority of epithelioid mesotheliomas studied for comparison. Calretinin expression was common in giant cell carcinomas (67%), small cell carcinomas (49%), and large cell carcinomas (38%), whereas it was rare in usual adenocarcinomas but slightly more common in those with neuroendocrine differentiation (11% and 17%, respectively). Thrombomodulin was present in all keratinizing squamous carcinomas and the great majority (87%) of nonkeratinizing tumors in a membrane-staining pattern. It was moderately common in small cell (27%) and large cell carcinomas (25%) but relatively rare in adenocarcinomas (13%). Keratin 5 was expressed in all keratinizing and the great majority (87%) of nonkeratinizing squamous carcinomas, and a majority of large cell carcinomas (56%) and some small cell carcinomas (27%). It was rare in acinar adenocarcinomas (12%) and absent in those with neuroendocrine differentiation. Mesothelin was present in more than half (53%) of adenocarcinomas and a minority (13%) of large cell carcinomas but was absent in small cell carcinomas. In squamous carcinomas it was more often seen in nonkeratinizing versus keratinizing tumors (31% vs 16%). These results show that each of these "mesothelioma" markers reacts with different subsets of pulmonary carcinomas with a variable frequency; this should be considered when using these markers in the differential diagnosis of thoracic tumors.

Immunocytochemistry of myoepithelial cells in the salivary glands

MECs are distributed on the basal aspect of the intercalated duct and acinus of human and rat salivary glands. However, they do not occur in the acinus of rat parotid glands, and sometimes occur in the striated duct of human salivary glands. MECs, as the name implies, have structural features of both epithelial and smooth muscle cells. They contract by autonomic nervous stimulation, and are thought to assist the secretion by compressing and/or reinforcing the underlying parenchyma. MECs can be best observed by immunocytochemistry. There are three types of immunocytochemical markers of MECs in salivary glands. The first type includes smooth muscle protein markers such as alpha-SMA, SMMHC, h-caldesmon and basic calponin, and these are expressed by MECs and the mesenchymal vasculature. The second type is expressed by MECs and the duct cells and includes keratins 14, 5 and 17, alpha 1 beta 1 integrin, and metallothionein. Vimentin is the third type and, in addition to MECs, is expressed by the mesenchymal cells and some duct cells. The same three types of markers are used for studying the developing gland. Development of MECs starts after the establishment of an extensively branched system of cellular cords each of which terminates as a spherical cell mass, a terminal bud. The pluripotent stem cell generates the acinar progenitor in the terminal bud and the ductal progenitor in the cellular cord. The acinar progenitor differentiates into MECs, acinar cells and intercalated duct cells, whereas the ductal progenitor differentiates into the striated and excretory duct cells. Both in the terminal bud and in the cellular cord, the immediate precursors of all types of the epithelial cells appear to express vimentin. The first identifiable MECs are seen at the periphery of the terminal bud or the immature acinus (the direct progeny of the terminal bud) as somewhat flattened cells with a single cilium projecting toward them. They express vimentin and later alpha-SMA and basic calponin. At the next developmental stage, MECs acquire cytoplasmic microfilaments and plasmalemmal caveolae but not as much as in the mature cell. They express SMMHC and, inconsistently, K14. This protein is consistently expressed in the mature cell. K14 is expressed by duct cells, and vimentin is expressed by both mesenchymal and epithelial cells. After development, the acinar progenitor and the ductal progenitor appear to reside in the acinus/intercalated duct and the larger ducts, respectively, and to contribute to the tissue homeostasis. Under unusual conditions such as massive parenchymal destruction, the acinar progenitor contributes to the maintenance of the larger ducts that result in the occurrence of striated ducts with MECs. The acinar progenitor is the origin of salivary gland tumors containing MECs. MECs in salivary gland tumors are best identified by immunocytochemistry for alpha-SMA. There are significant numbers of cells related to luminal tumor cells in the non-luminal tumor cells that have been believed to be neoplastic MECs.

Immunohistochemical diagnosis of epithelioid mesotheliomas: a critical review of old markers, new markers

Numerous new immunohistochemical markers that can be used in the diagnosis of mesothelioma have recently become available. As a result, new panels of antibodies that could be useful for distinguishing between epithelioid mesotheliomas and adenocarcinomas have been proposed. However, great differences of opinion exist regarding the individual value of some of these markers, especially when compared with those whose value has already been established. This article provides a critical review of the currently available information on those markers that could be useful in the diagnosis of epithelioid mesotheliomas or whose utility remains controversial. A practical approach to the diagnosis of these tumors is also provided.

Hepatocyte antigen as a marker of hepatocellular carcinoma: an immunohistochemical comparison to carcinoembryonic antigen, CD10, and alpha-fetoprotein

Hepatocyte monoclonal antibody (Hep) (alternatively Hep Par 1 for Hep paraffin 1) has been reported to stain normal hepatic tissue and hepatocellular carcinoma (HCC) with high specificity. We have studied the Hepatocyte expression in 96 cases of HCC and 311 cases of nonhepatic epithelial tumors. All cases of HCC were also stained with CEA-Gold 5, CD10, and alpha-fetoprotein. Hep, CEA-Gold 5, CD10, and alpha-fetoprotein immunostains were performed on formalin-fixed, paraffin-embedded tissue sections. Hep immunoreactivity was detected in 88 of 96 cases of HCC (92%), with a cytoplasmic and granular pattern of staining. The level of Hep expression in HCC corresponded to the nuclear grade and growth pattern. All 50 cases of nuclear grade 1 and nuclear grade 2 HCC were positive (100%), whereas 37 of 44 nuclear grade 3 (84%) and 1 of 2 nuclear grade 4 (50%) were positive. Sixty-seven of 68 cases of HCC with a trabecular, pseudoglandular, or scirrhous growth pattern were positive (98%), whereas 22 of 27 cases of HCC with a compact growth pattern were positive (81%). CEA-Gold 5, CD10, and alpha-fetoprotein immunoreactivity was detected in 76% (73 of 96), 52% (50 of 96), and 31% (30 of 96) cases of HCC, respectively. The positive predictive value of the combination of all four antibodies was 97%. Three cases of HCC were negative for all four antibodies; these cases had a high nuclear grade or a sarcomatoid or compact growth pattern. Twenty of 311 cases of nonhepatic tumors were positive for Hep (6%): 15 were adenocarcinomas and five were neuroendocrine tumors. The negative predictive value of Hep in HCC was 94%. The Hep-positive nonhepatic epithelial tumors were easily distinguished from HCC by the expression of keratin 7 or keratin 20 for adenocarcinoma and chromogranin and synaptophysin for neuroendocrine tumors because HCC does usually not express these markers. With the exception of two cases of hepatoid gastric carcinoma, all Hep-positive nonhepatic epithelial tumors were negative for alpha-fetoprotein, CEA-Gold 5, and CD10. Our study demonstrates that Hep is a relatively specific marker for HCC. It is useful in differentiating HCC from primary hepatic cholangiocarcinoma and metastatic tumors when combined with other immunomarkers.

Keratin expression in human tissues and neoplasms

Keratin expression in human tissues and neoplasms Keratin filaments constitute type I and type II intermediate filaments (IFs), with at least 20 subtypes named keratin 1-20. Since certain keratin subtypes are only expressed in some normal human tissues but not others, and vice versa, various tissues have been subclassified according to the pattern of keratin staining. Simple epithelia generally express the simple epithelial keratins 7, 18, 19, and 20, while complex epithelia express complex epithelial keratins 5/6, 10, 14, and 15. When an epithelium undergoes malignant transformation, its keratin profile usually remains constant. The constitution and expression patterns of keratin filaments in human epithelial neoplasms are complex and often distinctive. In this article, we first briefly review the molecular and cell biology of keratin filaments. We then focus on the expression patterns of keratin filaments in various human neoplasms.

Expression of cytokeratin 5/6 in epithelial neoplasms: an immunohistochemical study of 509 cases

Cytokeratin 5/6 (CK 5/6) immunoreactivity has been observed in the vast majority of cases of malignant mesothelioma but only rarely in pulmonary adenocarcinomas. Thus, CK 5/6 has been used to distinguish malignant mesothelioma from pulmonary adenocarcinoma. However, the utility of CK 5/6 in distinguishing pleural malignant mesothelioma from pleural metastases from nonpulmonary adenocarcinoma, as well as peritoneal malignant mesothelioma from peritoneal metastatic adenocarcinoma, has not yet been adequately addressed because the tissue expression of CK 5/6 in nonpulmonary neoplasms has not been well defined. We have studied the CK 5/6 expression in 509 cases of various epithelial tumors by immunohistochemistry. We found that the vast majority of cases of squamous cell carcinoma, basal cell carcinoma, thymoma, salivary gland tumor, and biphasic malignant mesothelioma were positive for CK 5/6. In addition, CK 5/6 immunoreactivity was detected in 15 of 24 cases (62%) of transitional cell carcinoma, in 5 of 10 cases (50%) of endometrial adenocarcinoma, in about one third of cases of pancreatic adenocarcinoma (38%) and breast adenocarcinoma (31%), and in one quarter of cases of ovarian adenocarcinomas (25%). Our study confirms the diagnostic utility of CK 5/6 immunohistochemistry in distinguishing biphasic mesothelioma from pulmonary adenocarcinoma but raises caution about its use for the differential diagnosis of pleural or peritoneal malignant mesothelioma versus pleural or peritoneal metastatic nonpulmonary adenocarcinoma, because many types of nonpulmonary adenocarcinomas may be positive for CK 5/6.

Thymic hyperplasia and lung carcinomas in a line of mice transgenic for keratin 5-driven HPV16 E6/E7 oncogenes

Human Papillomavirus type 16 (HPV-16) is the cause of both benign lesions and ano-genital cancers. In HPV-associated cancers the transforming properties of the expressed viral E6 and E7 proteins have been revealed by a number of different assays. We have generated transgenic mice expressing HPV-16 E6/E7 genes under the control of the murine keratin 5 gene promoter, which should confer cell-type specific expression in the basal cells of squamous stratified epithelia. Transgenic mice developed thymic hyperplasia and lung neoplasia with 100% frequency, the thymus showing a size increase at 2 months and reaching the maximum dimension at 6 months, when lung carcinomas appeared. After this time the size of hyperplastic thymi decreased, while malignant formations invaded the mediastinal area. Hepatic metastasis could be also observed in some of the animals at the autopsy and death invariably occurred around 10-11 months of age.

Immunohistochemical differential diagnosis of pleural effusions, with emphasis on malignant mesothelioma

The immunohistochemical diagnosis of atypical epithelial proliferations in pleural fluid is a challenging topic in cytopathology and surgical pathology. Mesothelioma may be simulated clinically and radiologically by several other nonneoplastic and neoplastic disorders, mandating that strict histologic, histochemical, immunohistochemical, and ultrastructural guidelines be followed for its diagnosis. Because of its availability to most laboratories, immunohistochemistry has emerged as the most commonly used procedure for the diagnosis of pleural malignancies. This review considers the current status of that investigative modality, with particular attention to lesions that are suspected to be mesothelial.

Calretinin and other mesothelioma markers in synovial sarcoma: analysis of antigenic similarities and differences with malignant mesothelioma

Synovial sarcoma (SS) is a mesenchymal neoplasm that typically shows epithelial differentiation. SS commonly metastasizes to lung and pleura, and has also been reported as the primary in these locations. The histologic distinction of SS from mesothelioma may be difficult because of the combination of epithelioid and spindle cells, potentially shared locations, and antigenic expression. In this study the authors examined 103 well-documented SSs including 41 biphasic, 44 monophasic, and 18 poorly differentiated SSs in comparison with 23 epithelioid and seven sarcomatous mesotheliomas. Most biphasic SSs (29 of 41, 71%) had fields or foci of calretinin-positive tumor cells. The spindle cell components were more often positive (55%), whereas 14% of tumors had positive epithelial cells. The monophasic and poorly differentiated SSs commonly had foci of calretinin-positive cells (in 52% and 56% of cases respectively). In comparison, all 23 epithelioid mesotheliomas (EM) were extensively calretinin positive and seven sarcomatoid mesotheliomas were variably calretinin positive. HBME-1 positivity was similarly detected in biphasic SS and EM (100% and 87% respectively). Among the other sarcomas, two of 15 malignant peripheral nerve sheath tumors were focally calretinin positive, whereas 16 epithelioid sarcomas, 20 leiomyosarcomas, 20 gastrointestinal stromal tumors, and 20 angiosarcomas were negative. Biphasic SSs differed from mesotheliomas by their more common BerEp4 positivity (90%) whereas EMs showed focal reactivity in 13% cases. Marked CD15 reactivity was rare in both. Wilms tumor protein-1 (WT1) was not detected in SS, but was present in 12 of 17 EMs. CD141 was rare in SS, limited to spindle cell components, whereas EMs typically showed prominent membrane staining in epithelial cells. Simple epithelial keratins were present in all epithelial cells of biphasic SS and mesothelioma (keratin 7[K7], K19), but were only focal in monophasic and poorly differentiated SS. Biphasic SSs were extensively K14 positive (89% of cases), whereas epithelial and sarcomatoid mesotheliomas typically showed only scattered positive cells. The potentially shared calretinin patterns in SS and mesothelioma require the use of other markers. The discriminating features include extensive BerEp4 positivity, rarity of CD141, and lack of WT1 in SS. Global expression of K7 and K19 in mesotheliomas versus focal expression in monophasic and poorly differentiated SSs, and differential patterns of K14 expression may also be helpful.

Anti-mesothelial markers in sarcomatoid mesothelioma and other spindle cell neoplasms

AIMS

To undertake a comparative evaluation of three antimesothelial markers (thrombomodulin, cytokeratin 5/6 and calretinin) with broad spectrum cytokeratin (AE1/AE3) in differentiating between sarcomatoid mesothelioma and a spectrum of spindle cell neoplasms.

METHODS AND RESULTS

Thirty-one malignant sarcomatoid mesotheliomas were studied. Calretinin expression was focally identified in 12 (39%) tumours and thrombomodulin and cytokeratin 5/6 immunoreactivity was seen in nine (29%) cases. In comparison there was strong diffuse cytoplasmic reactivity with the broad spectrum cytokeratin (AE1/AE3) in 24 of 31 (77%) tumours. Thirty mixed spindle cells neoplasms were studied. No calretinin expression was identified in any case. Thrombomodulin immunoreactivity was identified in four (16%) cases (two angiosarcomas, two high-grade sarcomas, not otherwise specified). Cytokeratin 5/6 expression was seen in one high-grade pulmonary sarcoma originally termed malignant fibrous histiocytoma. None of the antimesothelial markers was expressed in the four spindle cell carcinomas studied. In contrast, broad spectrum cytokeratin was diffusely expressed in all four spindle cell carcinomas (three pulmonary, one renal), both synovial sarcomas, both malignant mixed Müllerian tumours, one of three pulmonary leiomyosarcomas and two of nine sarcomas, not otherwise specified.

CONCLUSIONS

Immunohistochemistry has a more limited role in the diagnosis and distinction of sarcomatoid mesothelioma from other spindle cell neoplasms. The combination of a broad spectrum cytokeratin with calretinin combines both high sensitivity (77% for AE1/AE3) with high specificity (100% for calretinin) for sarcomatoid mesothelioma and can be diagnostically useful. The mesothelial markers, thrombomodulin and cytokeratin 5/6, are not useful alone in the diagnosis of sarcomatoid mesothelioma as each shows insufficient antibody sensitivity, although together they complement calretinin.

Glycogen-rich mesothelioma

A glycogen-rich epithelial mesothelioma is described. This variant is uncommon, but important to recognize since it is readily confused on routine light microscopy with other clear cell tumors involving the pleura. Ultrastructural and immunohistochemical studies can be helpful in establishing the correct diagnosis. Significant recent advances in the immunohistochemistry of epithelial mesothelioma are briefly reviewed.

Value of cytokeratin 5/6 immunostaining in distinguishing epithelial mesothelioma of the pleura from lung adenocarcinoma

The immunohistochemical diagnosis of mesothelioma is commonly made by using a battery of antibodies that reacts with lung adenocarcinomas but not with epithelial mesotheliomas. Only recently have markers that are often expressed in mesotheliomas but not in adenocarcinomas been recognized. Some of these markers, however, require frozen tissue sections, whereas others are not commercially available, or their value remains controversial. In a recent publication, it was suggested that immunostaining for cytokeratin 5/6 could assist in distinguishing epithelial mesothelioma from lung adenocarcinoma. To determine the practical value of cytokeratin 5/6 immunostaining in the diagnosis of mesothelioma, 40 formalin-fixed, paraffin-embedded epithelial pleural mesotheliomas, 30 pulmonary adenocarcinomas, 93 nonpulmonary adenocarcinomas, 15 squamous carcinomas of the lung, 5 large cell undifferentiated carcinomas of the lung, and 12 metastatic transitional cell carcinomas to the lung were stained with the same antibody, which was obtained from a commercial source. Cytokeratin 5/6 reactivity was observed in all 40 mesotheliomas, but there was none in any of the 30 pulmonary adenocarcinomas. Focal or weak reactivity was observed in 14 of 93 nonpulmonary adenocarcinomas (10 of 30 ovarian, 2 of 10 endometrial, 1 of 18 breast, I of 7 thyroid, 0 of 10 kidney, 0 of 10 colonic, and 0 of 8 prostatic). All 15 squamous carcinomas of the lung, 6 of 12 transitional cell carcinomas metastatic to the lung, and 3 of 5 large cell undifferentiated carcinomas of the lung expressed cytokeratin 5/6. It is concluded that cytokeratin 5/6 immunostaining is not only useful in separating epithelial pleural mesotheliomas from pulmonary adenocarcinomas but also can assist in distinguishing epithelial mesotheliomas from nonpulmonary adenocarcinomas metastatic to the pleura.

Role of immunohistochemistry in distinguishing epithelial peritoneal mesotheliomas from peritoneal and ovarian serous carcinomas

The histologic distinction between epithelial peritoneal mesothelioma and papillary serous carcinoma diffusely involving the peritoneum may be difficult. Although some investigators have indicated that immunohistochemistry can facilitate this differential diagnosis. only a few studies using a limited number of markers have been published. In this study, the immunoreactivity of keratin 5/6, vimentin, epithelial membrane antigen, thrombomodulin, calretinin, MOC-31, Ber-EP4, carcinoembryonic antigen, TAG-72 (B72.3), CD15 (Leu-M1), placental alkaline phosphatase, CA19-9, CA-125, HBME-1, 44-3A6, and S-100 protein was investigated in 35 epithelial peritoneal mesotheliomas, and 45 papillary serous carcinomas [30 ovarian (10 primary and 20 metastatic to the peritoneum) and 15 papillary serous carcinomas of the peritoneum]. After analyzing the results, it is concluded that calretinin, thrombomodulin, and keratin 5/6 are the best positive markers for differentiating epithelial malignant mesotheliomas from papillary serous carcinomas diffusely involving the peritoneum. The best diagnostic discriminators among the antibodies considered to be negative markers for mesothelioma are MOC-31, B72.3, Ber-EP4, CA19-9, and Leu-M1. Immunostaining for carcinoembryonic antigen, placental alkaline phosphatase, epithelial membrane antigen, vimentin, HBME-1, 44-3A6, CA-125, or S-100 have little or no diagnostic utility in establishing the differential diagnosis between these conditions. The results of this study also confirm previous observations indicating that both papillary serous carcinomas of the peritoneum and serous carcinomas of the ovary have a similar phenotype and, therefore, immunohistochemical studies are not useful in separating these entities.

Altered expression of epithelial cell surface glycoconjugates and intermediate filaments at the margins of mucosal wounds

Alterations in cell to cell adhesion are necessary to enable the type of cell movements that are associated with epithelial wound healing and malignant invasion. Several studies of transformed cells have related epithelial cell movement to changes in the cell surface expression of the carbohydrate structures represented by the ABO blood group antigens and, in particular, by Lewis antigens and their biosynthetic precursors. To study further the relationship between cell surface carbohydrates and keratinocyte cell movement, experimental wounds were created in human oral mucosa and examined by immunohistochemical methods for their expression of selected cytokeratins (K5, K16, K19), basement membrane components (laminin alpha5 and gamma2-chains, BP180, collagen IV and collagen VII), and blood group antigen precursor structures Le(x), sialosyl-Le(x), Le(y), H antigen, N-acetyllactosamine, and sialosyl-T antigen. The changes induced by wounding in the expression of collagen IV, laminin gamma2-chain (laminin-5), and laminin alpha5-chain were similar to those found in skin wounds and served to define the region of epithelial movement. This region was found to show a marked increase in staining for both Lewis antigen Y (Le(y)) and H blood group antigen, and decreased staining of Le(x), thus indicating an upregulation in wounded epithelium of the fucosyltransferases responsible for the synthesis of the H antigen. The changes in carbohydrate expression extended beyond the wound margin into the nonwounded epithelium, a pattern of expression similar to K16, which was also strongly upregulated in both the outgrowth and the adjacent nonwounded epithelium. These findings provide further support for an influence of such carbohydrate structures on the migratory behavior of epithelial cells.

Number and proliferation of basal and parabasal cells in normal human airway epithelium

Two roles have been suggested for basal cells on the basis of studies performed with laboratory animals: (1) anchoring of the tracheobronchial epithelium; and (2) being the epithelial stem cell. Parabasal cells located just above the basal cells have also been shown to contribute to cell renewal. However, a systematic study of the composition and proliferation of basal and parabasal cells in normal human lungs is lacking. The aims of this study were to determine in normal human conducting-airway epithelium: (1) the number of basal and parabasal cells; and (2) the contribution of basal and parabasal cells to the proliferation fraction. Samples of histologically normal tissue, free of pulmonary disease, were taken from seven lungs obtained by autopsy. Immunohistochemical staining was performed with the primary antibody MIB-1 as a proliferation marker and the antikeratin antibody 34betaE12 as a marker for basal and parabasal cells. In the largest conducting airways (diameter >= 4 mm), the percentages of basal and parabasal cells were 31% and 7%, respectively; the contribution to the proliferation compartment was 51% for basal and 33% for parabasal cells. In the smallest airways (diameter < 0.5 mm), 6% of epithelial cells were basal cells, with a 30% contribution to the proliferation compartment, whereas parabasal cells were absent. The high fraction of basal and parabasal cells contributing to the proliferation compartment of normal human conducting-airway epithelium supports the theory that cells at or near the basement membrane are likely to be progenitor cells.