Benign papillary mesothelioma of peritoneum: a histological, histochemical and ultrastructural study of six cases

Six cases of localized benign papillary mesothelioma of peritoneum were retrieved from laboratory files over a 20-year period. One presented because of pain following torsion and the remaining five were incidental findings at operation. Light microscopy showed a delicate papillary stroma covered by a single layer of mesothelial cells. The mesothelial cells often showed punctate periodic acid-Schiff staining of cytoplasm. The brush border and stroma showed alcian blue positive staining which was abrogated by prior incubation with hyaluronidase. Electron microscopy revealed typical features of mesothelial cells with long microvilli, rough endoplasmic reticulum in relation to mitochondria, bundles of microfilaments, and tight junctions. Between cells there was a series of intercommunicating channels containing occasional lymphocytes and debris. These features are compared with nodular mesothelial hyperplasia, malignant mesothelioma and adenomatoid tumours of the genital tract. The necessity to distinguish benign papillary mesothelioma from metastatic carcinoma is stressed and relies on the recognition of their mesothelial origin.     

Cytopathologic differential diagnosis of malignant mesothelioma, adenocarcinoma and reactive mesothelial cells: A logistic regression analysis

Distinguishing malignant mesothelioma, adenocarcinoma and reactive mesothelial proliferation in both cytologic and surgical pathologic specimens is often a diagnostic challenge. Conventional cytomorphologic assessment is an important step in the differential diagnosis of these entities.The pleural effusion cytologies from 40 cases of malignant mesothelioma, 40 cases of adenocarcinoma and 30 cases of reactive mesothelial proliferation diagnosed between 1997 and 2007 were reviewed. Twenty-seven cytologic features which are regarded as useful in the differential diagnosis of mesothelioma, adenocarcinoma and benign mesothelial proliferation were assessed. These cytologic features were subjected to a stepwise logistic regression analysis. Three features were selected to distinguish malignant mesothelioma from adenocarcinoma: giant atypical mesothelial cell (P = 0.0001), nuclear pleomorphism (P = 0.0001) and acinar structures (P = 0.0001), the latter two being characteristics of adenocarcinoma. The variables selected to differentiate malignant mesothelioma from reactive mesothelial cells were: cell ball formation (P = 0.0001), cell in cell engulfment (P = 0.0001) and monolayer cell groups (P = 0.0001), the latter being a feature of benign mesothelial proliferation. When these selected variables were subjected to a stepwise logistic regression analysis, the logistic model correctly predicted 90% of cases of benign mesothelial proliferation versus 97.5% of malignant mesothelioma and 92.5% of malignant mesothelioma versus 92.5% of adenocarcinoma.Conventional cytomorphologic assessment is the first step to establish an accurate diagnosis in pleural effusions. Several cytologic features have predictive value to separate malignant mesothelioma from adenocarcinoma and reactive mesothelial proliferation.     

Immunohistochemical positivity for neuron-specific enolase and Leu-7 in malignant mesotheliomas.

The discovery of immunostaining for neuron-specific enolase (NSE) and Leu-7 in a small cell mesothelioma prompted us to study some putative immunohistochemical markers of neuroendocrine differentiation in malignant mesotheliomas and to examine any diagnostically important immunohistochemical distinctions or similarities between malignant mesothelioma and other histologically similar lung tumours. Most mesotheliomas were positive for NSE (96 per cent) and Leu-7 (70 per cent) and positivity for these two markers was also found in small cell carcinomas (NSE 25 per cent, Leu-7 81 per cent) and adenocarcinomas (NSE 28 per cent, Leu-7 28 per cent) but carcinosarcomas were positive for only NSE (44 per cent). Chromogranin A positivity was found only in occasional small cell carcinomas (6 per cent) and adenocarcinomas (6 per cent). No tumour was positive for bombesin. The high incidence of NSE and Leu-7 positivity in mesotheliomas is an important original observation because it guards against the unjustified exclusion of mesothelioma from a differential diagnosis on the basis of positivity for these two markers.     

Pathology of malignant mesothelioma

The diagnosis of malignant mesothelioma can pose several problems to the surgical pathologist. First, the morphological appearances of the tumour are known to be diverse with mimicry of a range of both reactive and neoplastic conditions. Second, due to the relative inaccessibility of the serosa, biopsy material is often scanty and fragmentary, producing a plethora of interpretive ambiguities. Third, adjunct techniques such as mucin histochemistry and immunohistochemistry, whilst useful in excluding malignant mesothelioma have little role in confirming the diagnosis. The accurate diagnosis of diffuse malignant mesothelioma is important for two reasons: (1) In relation to prognosis as it has an almost invariable fatal outcome, which contrasts with the other mesothelial neoplasms such as the benign adenomatoid tumour and the borderline malignant tumours, namely the well-differentiated papillary mesothelioma and multicystic mesothelioma; (2) In relation to occupational-related compensation claims following asbestos exposure. This review summarizes the aetiology of asbestos-induced neoplasia, possible mechanisms of tumour development and highlights potential diagnostic pitfalls.     

Immunocytochemistry of malignant mesothelioma: OV632 as a marker of malignant mesothelioma.

In pleural or ascitic effusions the cytomorphological distinction of adenocarcinoma cells, reactive mesothelial cells, and malignant mesothelioma cells often causes a diagnostic dilemma. The value of immunocytochemistry was investigated on cytological smears of 24 well-established cases of malignant mesothelioma, a selected series of 31 metastatic adenocarcinomas, and 20 smears of patients without known malignancy. In these smears we scored the immunoreactivity with a panel of four monoclonal antibodies. In addition to antibodies for epithelial membrane antigen (EMA) and carcinoembryonic antigen (CEA), the monoclonal antibody MOC31 and the ovarian carcinoma specific antibody OV632 were incorporated in the panel. With none of these four antibodies was immunostaining of reactive mesothelial cells found. CEA- and MOC31-positive tumour cells were frequent in metastatic adenocarcinomas, but occurred rarely in malignant mesotheliomas. EMA-positive tumour cells were found in all metastatic adenocarcinomas (100 per cent) and in most malignant mesotheliomas (83 per cent). In addition to the expected reactivity of OV632 with ovarian carcinomas, 22 of 24 malignant mesotheliomas contained immunopositive tumour cells, while only a small proportion of non-ovarian adenocarcinomas reacted with this antibody. This selective staining of malignant mesothelioma cells, but not reactive mesothelial cells, with OV632 now permits the positive identification of malignant mesothelioma cells in male patients.     

Solitary (localized) fibrous mesothelioma: evidence against mesothelial cell origin

Five cases of solitary (localized) fibrous mesothelioma were studied immunohistochemically, utilizing monoclonal antibodies against high and low molecular weight cytokeratin, vimentin, carcinoembryonic antigen, epithelial membrane antigen and factor VIII related antigen. In contrast to normal mesothelium and contrary to previous reports from malignant mesotheliomas all the tumours were negative for keratin. They were strongly positive for vimentin. Two cases were studied electron microscopically; no ultrastructural evidence of mesothelial cell differentiation was identified. Our immunohistochemical and ultrastructural findings argue against a mesothelial cell origin, whereas the presence of vimentin suggests a mesenchymal histogenesis. It is postulated that these tumours arise from sub-mesothelial mesenchymal connective tissue.     

The expression of CXCR4, CXCL12 and CXCR7 in malignant pleural mesothelioma

The chemokine CXCL12 and its receptors, CXCR4 and CXCR7, are involved in tumour progression, metastasis, and survival. We investigated the expression of CXCR4, CXCL12, and CXCR7 in malignant pleural mesothelioma to determine if they are possible biomarkers and potential therapeutic targets. Forty-one mesothelioma tumour tissues, ten normal human pleural tissues, and two mesothelioma cell lines were stained with anti-CXCR4, anti-CXCL12, anti-CXCR7, and anti-p-Akt antibodies. RT-PCR was performed to determine the expression of CXCR4, CXCL12, and CXCR7 in six human mesothelioma cell lines (H28, 211H, H2052, ms-1, H290, and H513) and one human normal mesothelial cell line, LP9. These seven cell lines were also stained with anti-CXCR7. We found that CXCR4 and CXCL12 were expressed in 97.6% and 78.0% mesothelioma tissue samples, concurrently with strong expression of p-Akt (R(2) = 0.739 and 0.620, respectively). In addition, CXCR7 expression was weaker than CXCR4 expression in mesothelioma tissues. Furthermore, RT-PCR showed that CXCR4 and CXCL12 were overexpressed in 5/6 mesothelioma cell lines (211H, H2052, ms-1, H290, and H513), whereas CXCR7 was overexpressed in only 2/6 (H513 and H2052). Moreover, we found that the CXCR4 antagonist AMD3100 inhibited the growth of all five mesothelioma cell lines that overexpress CXCR4 and CXCL12. Our results suggest that the Akt-mTOR pathway is involved during the interruption of the CXCL12/CXCR4 axis in these five mesothelioma cell lines. In conclusion, CXCR4 and CXCL12 are highly expressed in most mesothelioma cell lines and tumour tissues, suggesting that CXCR4 and CXCL12 may be used as biomarkers for patients with mesothelioma. The CXCL12-CXCR4 interaction may be a potential therapeutic target for mesothelioma.     

'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.     

Assessment of cell cycle state may facilitate the histopathological diagnosis of malignant mesothelioma

AIMS: The differentiation of benign pleural conditions from malignant mesothelioma may be difficult, especially with a small biopsy. We have tested the hypothesis that assessment of the cell cycle status is of value in the histopathological diagnosis of such biopsies, by comparing 33 malignant mesotheliomas with 36 cases of reactive mesothelial hyperplasia and reactive pleural fibrosis. METHODS AND RESULTS: Biopsies were investigated for proliferative status by immunostaining for a novel antibody, MCM2, all of which showed nuclear expression of MCM2 at higher frequency than Ki67 (P < 0.0001). Counts in areas of maximum tumour staining showed significantly higher labelling indices (LIMax) in epithelioid and sarcomatoid mesotheliomas compared with reactive mesothelial hyperplasia and reactive pleural fibrosis (P < 0.0001 for both). Average counts (LIAve) revealed a significant increase in epithelioid mesothelioma compared with reactive mesothelial hyperplasia (P < 0.0001). CONCLUSION: We consider MCM2 to be a useful adjunct in the differential diagnosis of malignant mesothelioma.     

Malignant epithelioid mesothelioma: anti-mesothelial marker expression correlates with histological pattern

AIMS: Malignant epithelioid mesothelioma shows marked cytoarchitectural diversity. The aim of the study was to evaluate how immunoreactivity with mesothelial markers related to histological pattern. METHODS AND RESULTS: Ninety-two cases of malignant epithelioid mesothelioma (60 pleural, 32 peritoneal) were examined and classified as exhibiting tubulopapillary, adenomatoid, solid, small cell or pleomorphic patterns. All cases were immunohistochemically stained with thrombomodulin, calretinin, CD44H, and cytokeratin 5/6. Cases of malignant mesothelioma exhibited a number of different histological forms. Immunohistochemical expression of each mesothelial marker tested was not homogeneous across different histological patterns of malignant epithelioid mesothelioma, even within the same tumour section. Calretinin (with nuclear expression) was identified to show the highest overall sensitivity and lowest range variation in staining (67% sensitivity in small cell areas to 100% expression in pleomorphic areas). Cytokeratin 5/6 and thrombomodulin yielded similar overall sensitivity. Thrombomodulin appeared to demonstrate higher sensitivity for small cell variant tumour (83% sensitivity). A notable advantage with cytokeratin 5/6 was that expression was more diffuse in nature rather than the focal membranous elaboration seen in thrombomodulin. The widest range of staining was seen in small cell mesothelioma (83% sensitivity with thrombomodulin to 17% sensitivity with cytokeratin 5/6) and in tubulopapillary areas (90% sensitivity with calretinin to 38% sensitivity with CD44H). CONCLUSIONS: Calretinin appears most useful and shows the highest overall sensitivity for malignant epithelioid mesothelioma, with good expression in areas displaying a tubulopapillary, adenomatoid, solid and pleomorphic pattern. For small cell mesothelioma, thrombomodulin appears to confer higher sensitivity and is advocated, in this setting, as the first line mesothelial marker. Cytokeratin 5/6 is a useful and easily interpretable mesothelial marker. CD44H is not of particular use in the diagnosis of malignant epithelioid mesothelioma. Accurate interpretation of immunohistochemistry in mesothelioma requires an awareness of the immunophenotypic heterogeneity identified in different histological forms of the tumour, and this is of particular importance in small biopsies.     

EXPRESSION OF ICAM-1 AND VCAM-1 IN HUMAN MALIGNANT MESOTHELIOMA

Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) are cytokine-inducible adhesion molecules which recognize ligands that are highly expressed on leukocytes. Expression of ICAM-1 and VCAM-1 was investigated in tissue sections of 16 cases of malignant mesothelioma (seven epithelial, eight biphasic, and one sarcomatoid) using immunohistochemistry. Neoplastic cells were diffusely and intensely stained for ICAM-1 in all cases. VCAM-1 was detected in 14 of 16 cases. The percentage of VCAM-1-positive tumour cells was more than 50 per cent in eight cases and the staining was observed mainly in epithelial-like cells. VCAM-1 was rarely expressed in other malignant tumours of epithelial origin, being present in only 1 of 58 cases of carcinoma originating from different anatomical sites. At the cellular level, ICAM-1 and VCAM-1 appeared co-distributed, the staining for both being cytoplasmic with a membrane reinforcement. The regulation of VCAM-1 expression by neoplastic mesothelial cells was investigated in vitro using 14 mesothelioma cell lines. ICAM-1 was expressed by cultured cells of all mesothelioma cell lines, even in the absence of cytokines. VCAM-1 was detected in 10–50 per cent of the cells in three non-stimulated mesothelioma cell lines (mero-95, mero-96, and mero-134), and was absent or poorly expressed in the remaining 11. Exposure of a negative cell line (mero-48a) to an optimal concentration of tumour necrosis factor alpha (TNFα) or interleukin-13 (IL-13) for 6–18 h resulted in the induction of VCAM-1 mRNA synthesis and in VCAM-1 expression at the membrane level in 60–70 per cent of the cells. These findings are consistent with the possibility that TNFα, IL-13, or other activating signals are released in the tumour micro-environment and regulate the expression of VCAM-1 in malignant mesothelioma cells.     

Malignant mesothelioma: cytologic diagnosis with histologic, immunohistochemical, and ultrastructural correlation.

The differential diagnoses of malignant mesothelioma in serous effusions include adenocarcinoma and reactive mesothelial cells. While several cytologic features are of predictive value in separating these entities, immunostaining and ultrastructural examination are important adjuncts that increase the diagnostic yield. Many of the cytomorphologic features can be correlated with immunohistochemical and ultrastructural findings. Most important among these is the ultrastructural demonstration of long, often branching microvillous processes in malignant mesothelial cells. Corresponding microvilli can be visualized by immunostaining for epithelial membrane antigen in both cell block preparations from effusions and biopsy specimens, allowing the identification of malignant mesothelioma. In addition, the circumferential distribution of these immunostained microvilli in cells dispersed in stromal connective tissue identifies them as malignant mesothelial cells, corresponding to the ultrastructural appearance of aberrant microvilli, which project through deficiencies in the basal lamina. These microvilli show interdigitation with stromal collagen fibers, a phenomena not observed in adenocarcinoma.     

Adenomatoid tumour of the uterus

Two adenomatoid tumours of the uterus were examined immunohistochemically using antibodies to keratin, Factor VIII related antigen, EMA, CEA and a specific protein isolated from mesothelioma cells. The tumour cells gave positive staining for keratin and for the specific mesothelial marker. The results strongly support a mesothelial origin for adenomatoid tumours and this panel of antibodies may be used to solve diagnostic problems.     

Papillary mesothelioma of ovary

A case of primary papillary mesothelioma of the ovary is reported and its microscopic and ultrastructural features described. This tumour was an incidental surgical finding and was accompanied by multiple, partially cystic, peritoneal lesions with similar microscopic features. The histological pattern was predominantly papillary with well-differentiated mesothelial cells and a prominent stromal infiltrate that included large numbers of lymphocytes and lipid-filled macrophages. A comparison is made with adenomatoid tumours and with other tumours of ovarian epithelium and it is suggested that this tumour may represent the benign counterpart of one form of clear cell carcinoma of the ovary. The presence of multiple peritoneal lesions may indicate limited malignant potential comparable to some other papillary epithelial neoplasms of the ovary.     

The histology and immunohistochemistry of small cell mesothelioma

The object of this study was to describe the histology and immunohistochemistry of 13 small cell mesotheliomas, concentrating on reliable distinctions between them and small cell carcinoma. All 13 tumours showed regions of more typical mesothelioma if multiple blocks were examined. No tumours showed the streams, ribbons, rosettes, or haematoxyphilic blood vessels that are typical of small cell carcinoma. Mitotic figures were relatively scarce and the nuclei had a particularly characteristic open appearance with prominent nucleoli and delicate chromatin. Nuclear moulding was not seen. No tumour produced neutral mucin. Immunohistochemical positivity for neuron-specific enolase (NSE) was found in 11/13, cytokeratin in 9/13 and Leu-7 in 4/13 but none was positive for chromogranin A, carcino-embryonic antigen (CEA) or leucocyte common antigen (LCA). We conclude that the accurate diagnosis of small cell mesothelioma is possible, provided that the clinical presentation is known, the tumour is adequately sampled and the microscopy carefully assessed. In small biopsy specimens, where the diagnosis is less straightforward, immunohistochemistry for CEA, and perhaps LCA and chromogranin A may be helpful. NSE and Leu-7 positivity is common in these tumours and might be misleading if interpreted as reliable evidence of neuroendocrine differentiation.     

Sarcomatous Type of Malignant Mesothelioma

Thirteen malignant mesotheliomas of a sarcomatous type were studied by light microscopy and ten were studied by electron microscopy. The histologic patterns varied from tumor to tumor, often resembling other soft tissue sarcomas. Electron microscopic observation showed most of the tumors to be composed of primitive cells. Despite their mesenchymal character, many tumors contained foci of rudimentary epithelial differentiation. It is concluded that both histologic types of malignant mesothelioma, the epithelial as well as the sarcomatous, originate from the same precursor cell at various points of its differentiation and reflect the range of maturation from the mesenchymal reserve cell to the epithelial mesothelial cell.     

Sarcomatous Type of Malignant Mesothelioma

Thirteen malignant mesotheliomas of a sarcomatous type were studied by light microscopy and ten were studied by electron microscopy. The histologic patterns varied from tumor to tumor, often resembling other soft tissue sarcomas. Electron microscopic observation showed most of the tumors to be composed of primitive cells. Despite their mesenchymal character, many tumors contained foci of rudimentary epithelial differentiation. It is concluded that both histologic types of malignant mesothelioma, the epithelial as well as the sarcomatous, originate from the same precursor cell at various points of its differentiation and reflect the range of maturation from the mesenchymal reserve cell to the epithelial mesothelial cell.     

Immunohistochemical phenotype of malignant mesothelioma: predictive value of CA125 and HBME-1 expression

Histological diagnosis of malignant mesothelioma and differentiation from adenocarcinoma is often difficult. Definitive pathological confirmation of malignant mesothelioma requires demonstration of an appropriate immunohistochemical phenotype. Selection of an optimum panel of immunohistochemical antibodies for the reliable identification of malignant mesothelioma is hindered by the absence of a specific immunohistochemical label for mesothelioma cells. Recently, we have found that the ovarian carcinoma cell antibody CA125 labels malignant mesothelioma cells, and the antibody HBME-1 has been developed as a sensitive mesothelial cell marker. We have compared the immunohistochemical staining patterns achieved with CA125 and HBME-1 to those obtained using a panel of eight further antibodies in 17 malignant mesotheliomas and 14 primary and secondary adenocarcinomas within lung and pleura. CA125 labelled malignant mesothelioma cells in 15 of 17 cases (88%), and adenocarcinoma cells in seven of 14 cases (50%). HBME-1 labelled mesothelioma cells in all 17 cases (100%) but also labelled adenocarcinoma cells in 10 of 14 cases (71%). BerEP4 positively labelled one malignant mesothelioma but was negative in the remaining 16 cases and positively labelled nine of 14 adenocarcinomas (64%). Monoclonal anti-CEA, AUA-1, CA19.9 and LeuM1 labelled no malignant mesotheliomas and were positive in 10 (71%), nine (64%), eight (57%) and six (43%) of 14 cases of adenocarcinoma, respectively. Diastase-PAS staining detected neutral mucin in none of the malignant mesotheliomas but in 10 (71%) of the 14 adenocarcinomas. We conclude that CA125 and HBME-1 do not label mesothelial cells with sufficient specificity to be useful for differentiating malignant mesothelioma from adenocarcinoma, although negative staining with HBME-1 makes a diagnosis of malignant mesothelioma unlikely. As there remains an absence of a specific positive mesothelial cell marker this distinction is still most reliably made using a panel of antibodies including at least two of the following: anti-CEA, AUA-1, BerEP4, LeuM1 and CA19.9, in combination with histochemical assessment of neutral mucin production.     

心包原发性恶性间皮瘤的临床病理分析

目的：探讨心包原发性恶性间皮瘤的临床病理特征。诊断与鉴别诊断要点。方法：对4例心包原发性恶性间皮瘤进行临床病理分析。光镜及免疫组化染色观察并复习有关文献。结果：男3例,女1例,平均年龄42岁,3例呈局限型,1例为弥漫浸润型。组织学上可表现为肉瘤样梭形细胞型,上皮样型及双相型,免疫组化染色显示肉瘤样梭形细胞表CK、vimentin;上皮样型瘤细胞表达HBME1、CK。结论：原发于心包的恶性间皮瘤罕见,预后极差。临床常被误诊,其组织形态亦复杂多样,应注意与心包的良性增生性病变,心包转移性腺癌和梭形细胞肿瘤等相鉴别。