The use of histological and immunohistochemical markers to distinguish pleural malignant mesothelioma and in situ mesothelioma from reactive mesothelial hyperplasia and reactive pleural fibrosis.

Distinguishing malignant mesothelioma from reactive mesothelial hyperplasia and reactive fibrosis can be a diagnostic problem in small pleural biopsies, made more difficult by the recent recognition of mesothelioma-in-situ. Antibodies to epithelial membrane antigen (EMA), p53, and bcl-2 have all been advocated for differentiating reactive from neoplastic conditions, but reports are inconsistent. These antibodies have therefore been applied to 31 cases of malignant mesothelioma, 34 cases of reactive pleural disease (20 reactive mesothelial hyperplasia and 14 reactive pleural fibrosis) and four small biopsies that were initially coded as suspicious, from patients who later developed frank mesothelioma. Thirty out of 31 (97 per cent) cases of mesothelioma showed positive nuclear staining for p53, with a higher incidence of positivity in epithelioid than in sarcomatoid elements and 30/31 (97 per cent) showed diffuse linear membrane staining for EMA, again more intense in the epithelioid elements. No mesothelioma was positive for bcl-2. In seven cases that contained both in situ and invasive mesothelioma, the in situ elements showed similar staining patterns to the invasive epithelioid elements. Thirteen out of 20 (65 per cent) cases of reactive mesothelial hyperplasia showed occasional nuclear positivity for p53 and 5/20 (25 per cent) cases showed focal weak membrane staining for EMA. Three out of 14 (21 per cent) cases of reactive pleural fibrosis showed positive nuclear staining for p53 and 6/14 (43 per cent) cases showed focal membrane staining with EMA. No reactive cases stained for bcl-2. All four suspicious cases showed diffuse linear staining with EMA and three showed focal staining for p53. It is concluded that strong diffuse linear staining for EMA is a good marker of malignancy when differentiating epithelioid malignant mesothelioma and mesothelioma-in-situ from reactive mesothelial hyperplasia, although weak focal staining may occur in reactive conditions. Nuclear staining for p53 is also suggestive of epithelioid mesothelioma, but should be regarded as no more than suspicious. The antibodies used in this investigation are less helpful in differentiating sarcomatoid mesothelioma from reactive pleural fibrosis.     

Unusual intraparenchymal growth patterns of malignant pleural mesothelioma

AIMS: Malignant pleural mesothelioma is known to mimic morphologically a number of diverse reactive and neoplastic conditions. We describe three unusual intraparenchymal growth patterns of malignant mesothelioma seen in a series of 200 malignant pleural mesotheliomas. The diagnostic pitfalls associated with these findings are described and their potential medico-legal implications are highlighted. METHODS AND RESULTS: The study group comprised 200 malignant pleural mesotheliomas. In each case diagnosis was morphologically confirmed with ancillary immunohistochemistry using a broad panel of both mesothelial and epithelial markers. The patterns of intraparenchymal growth were documented and grouped as: direct subpleural; lymphangitic; and other. The 200 malignant pleural mesotheliomas comprised 118 epithelioid, 57 biphasic and 25 sarcomatoid, subtyped according to the WHO classification. Direct subpleural invasion was seen in 42 cases, lymphangitic spread in 27 cases. Other less well-defined intraparenchymal patterns included three sarcomatoid subtype malignant mesotheliomas exhibiting an intra-alveolar growth pattern mimicking epithelioid haemangioendothelioma. One epithelioid subtype malignant mesothelioma contained an intraparenchymal tumour nodule microscopically comprising lepidic spread of neoplastic cells over maintained alveolar structures mimicking bronchioloalveolar carcinoma. One epithelioid subtype malignant mesothelioma morphologically had areas in which alveoli were distended by discohesive epithelioid neoplastic cells with no interstitial invasion. The appearances mimicked desquamative interstitial pneumonia. Immunohistochemistry played an important role in the definitive diagnosis of each unusual parenchymal tumour deposit. In 126 malignant mesotheliomas no invasion of the subjacent lung parenchyma was identified. CONCLUSIONS: An awareness of the unusual parenchymal growth pattern in malignant mesothelioma is important to prevent misdiagnosis of other entities. In the medico-legal setting, the presence of epithelioid haemangioendothelioma or bronchioloalveolar carcinoma (in the absence of asbestosis) may be deemed to impact upon the patient's anticipated life expectancy and thereby would decrease the compensation settlement.     

Morphologische Diagnostik maligner Pleuramesotheliome

The World Health Organization (WHO) classification differentiates between pleural tumors of mesothelial and mesenchymal origin as well as lymphoproliferative disorders, with malignant mesotheliomas forming the most common pleural primary tumor. Histologically, epithelioid (40–60?%), sarcomatoid (20–40?%), and biphasic mesotheliomas (20–40?%) are distinguished. The certain morphological diagnosis of a malignant pleural mesothelioma requires the establishment of mesothelial differentiation by means of an appropriate panel of antibodies to exclude pleural dissemination of a pulmonary or extrapulmonary epithelial malignancy and also requires the establishment of at least focal invasive growth to distinguish from reactive mesothelial proliferation. The exclusion of a malignant pleural mesothelioma may induce further differential diagnostic considerations, e. g. concerning the assignment to a certain primary tumor after the establishment of carcinomatous pleuritis.     

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.     

Keratin and epithelial membrane antigen immunoreactivity in nonneoplastic fibrous pleural lesions: implications for the diagnosis of desmoplastic mesothelioma

The histologic distinction between desmoplastic mesothelioma and reactive fibrosis and between biphasic desmoplastic mesothelioma and pleural metastases with desmoplasia can be difficult. The presence of such epithelial markers as keratin and epithelial membrane antigen (EMA) within the fibrous areas of a pleural lesion might be construed as evidence in support of the diagnosis of desmoplastic mesothelioma. To test this hypothesis ten desmoplastic mesotheliomas were studied with monoclonal antisera to keratin and EMA and compared with ten hyaline pleural plaques, 11 pleural scars, five benign localized fibrous mesotheliomas, and eight desmoplastic pleural metastases. Although the hyalinized fibrous areas within the desmoplastic mesotheliomas stained with keratin (ten of ten) and EMA (five of ten), the following reactive fibrous pleural lesions were also positive: plaques (four of ten keratin-positive, five of ten EMA-positive); scars (six of 11 keratin-positive, four of 11 EMA-positive); and fibrosis induced by metastases (six of eight keratin-positive, one of eight EMA-positive). Benign localized fibrous mesotheliomas were keratin- and EMA-negative. This study suggests that both benign and malignant fibrous pleural lesions may be of mesothelial origin and demonstrates the need to determine by histologic criteria whether the spindle cell component is benign or malignant before assessing the significance of its keratin or EMA immunoreactivity. The lack of keratin and EMA staining in benign localized fibrous mesotheliomas might be of use in distinguishing benign localized cellular fibrous mesotheliomas from sarcomatous mesotheliomas.     

Immunohistochemical expression of osteopontin in epithelioid mesotheliomas and reactive mesothelial proliferations

The morphologic distinction of epithelioid mesothelioma from a reactive mesothelial proliferation can be difficult. Recent studies have demonstrated that serum osteopontin levels are increased in patients with mesotheliomas. We sought to determine if osteopontin expression is diagnostically helpful in distinguishing epithelioid mesothelioma from reactive mesothelial proliferations. We studied 7 cases of epithelioid mesothelioma and 20 cases of reactive mesothelial proliferations by immunohistochemical analysis using standard technique. All 7 mesotheliomas and 19 of 20 reactive mesothelial proliferations showed osteopontin expression.Osteopontin expression is not restricted to malignant mesothelial proliferations, and immunohistochemical analysis for osteopontin is not helpful in determining reactive vs malignant mesothelial proliferations. The reported usefulness of osteopontin as a serum tumor marker for mesothelioma may be due to differences in the amount or character of secreted protein in malignant mesothelioma compared with reactive mesothelial proliferations.     

The use of immunohistochemistry in distinguishing reactive from neoplastic mesothelium. A novel use for desmin and comparative evaluation with epithelial membrane antigen,p53, platelet-derived growth factor-receptor,P-glycoprotein and Bcl-2

AIMS: To evaluate the expression of the intermediate filament desmin in reactive mesothelium and malignant mesothelioma and to compare its utility with five other previously reported immunomarkers claimed to be of use in distinguishing reactive from neoplastic mesothelium. METHODS AND RESULTS: Sixty cases of malignant pleural mesothelioma and 40 cases of reactive mesothelial hyperplasia formed the study group. Cases were immunohistochemically stained with desmin, epithelial membrane antigen (EMA), p53, Bcl-2, P-glycoprotein and platelet-derived growth factor receptor (PDGF-R) beta-chain by the avidin-biotin complex method. The cohort of malignant pleural mesotheliomas were immunoreactive to desmin, EMA and p53 in 6/60 (10%), 48/60 (80%) and 27/60 (45%), respectively. In comparison, the cohort of reactive mesothelial hyperplasias were immunoreactive to desmin, EMA and p53 in 34/40 (85%), 8/40 (20%) and 0/40 (0%), respectively. In a smaller cohort (n = 15) of malignant pleural mesotheliomas, Bcl-2, P-glycoprotein and PDGF-R beta-chain were expressed in 0/15 (0%), 2/15 (13%) and 15/15 (100%), respectively. In a small cohort (n = 15) of reactive mesothelial hyperplasias, Bcl-2, P-glycoprotein and PDGF-R beta-chain were immunoreactive in 0/15 (0%), 0/15 (0%) and 6/15 (40%), respectively. CONCLUSIONS: Desmin and EMA appear to be the most useful markers in distinguishing benign from malignant mesothelial proliferations. Desmin appears to be preferentially expressed in reactive mesothelium and EMA appears to be preferentially expressed in neoplastic mesothelium. The complementary use of both markers is advocated in ascertaining the nature of mesothelial proliferations. Immunohistochemical detection of mutated p53 oncoprotein appeared to be of less utility in this study on account of the low marker sensitivity for malignant mesothelioma. However, p53 antibody may be of use as a second-line marker of neoplastic mesothelium within a standard immunohistochemical panel of antibodies. In this study, Bcl-2, P-glycoprotein and PDGF-R beta-chain appear to be of no use in distinguishing reactive from neoplastic mesothelium, although more formal evaluation of these markers is required.     

Diagnostic importance of 9p21 homozygous deletion in malignant mesotheliomas.

Definitive diagnosis of malignant mesothelioma in small specimens can be extremely difficult based on morphology alone. Homozygous deletion of 9p21, the locus harboring the p16 gene, has been reported as the most common genetic alteration in malignant mesotheliomas. Recent studies demonstrated that this alteration may be useful for differentiating benign from malignant mesothelial proliferations in cytology specimens. The aim of this study was to evaluate the diagnostic utility of homozygous deletion of 9p21 assessed by fluorescence in situ hybridization (FISH) in mesothelial proliferations involving serosal surfaces in paraffin-embedded tissue. p16 protein immunoexpression was also explored as a potential diagnostic aid. FISH analysis demonstrated homozygous deletion of the 9p21 locus in 35 of 52 cases (67%) of pleural mesothelioma and in 5 of 20 cases of peritoneal mesothelioma (25%) (P<0.005). None of 40 cases of reactive pleural mesothelial proliferations showed p16 deletion (P<0.005). Loss of immunoexpression of p16 was observed in 71% of the peritoneal mesotheliomas, 40% of the pleural malignant mesotheliomas and 15% of the reactive mesothelial cells. Homozygous deletion did not correlate with p16 protein expression in any of the studied groups. Our study suggests that 9p21 homozygous deletion assessed by FISH on paraffin-embedded tissue may be helpful for differentiating between malignant mesotheliomas and reactive mesothelial proliferations. A discrepancy between p16 protein expression and homozygous deletion suggests that other molecular mechanisms may play a role in p16 protein expression in mesothelial proliferations.     

β-catenin expression in benign and malignant pleural disorders

Benign and malignant pleural processes display a large and overlapping spectrum of morphological appearances, and can be difficult to distinguish, histologically, from each other. β-catenin, a participant in the wingless-type (Wnt) transduction pathway, is involved in the pathogenesis of malignant mesothelioma and has received limited evaluation for its ability to serve as a diagnostic aid for distinguishing between individual pleural disorders. We performed immunohistochemistry for β-catenin on 10 pleural malignant mesotheliomas, 10 examples of mesothelial hyperplasia and 18 cases of organizing pleuritis. Although differences were noted in staining intensity between the mesothelioma and mesothelial hyperplasia groups, extensiveness and cellular location were similar. Staining intensity (mean +/- s.d.) in mesotheliomas (2.00 +/- 0.67) was significantly less intense than in mesothelial hyperplasia cases (3.00 +/- 0.00) (p=0.0005). Stromal cell staining was cytoplasmic in all cases, and endothelial cell staining was membranous, submembranous and cytoplasmic. Nuclear expression of β-catenin was not observed in any of the cases studied. This lack of nuclear staining in the stromal cells of organizing pleuritis differs markedly from the previously reported high frequencies of nuclear β-catenin expression in other pleural spindle cell proliferations (desmoid tumors and solitary fibrous tumors). In summary, the current study adds to previous work indicating a role for β-catenin in the genesis of pleural conditions including organizing pleuritis, mesothelial hyperplasia and malignant mesothelioma. Although IHC for β-catenin does not appear to be conclusive for separating benign from malignant mesothelial proliferations, it may be valuable for assisting in the differential diagnosis of mesothelial and spindle cell proliferations in the pleura.     

p53 immunostaining in the distinction between benign and malignant mesothelial proliferations using formalin-fixed paraffin sections.

The distinction between reactive mesothelium and mesothelioma in pleural biopsy specimens is notoriously difficult, and conventional immunohistochemical markers have provided no relief. The object of this study was to examine the frequency of immunohistochemically detectable p53 overexpression in routinely processed, paraffin-embedded tissue from pleural mesotheliomas and from pleura showing reactive mesothelial hyperplasia, using a polyclonal antibody to formalin-resistant p53 epitopes, and to consider the diagnostic utility of this antibody in the distinction between mesothelioma and reactive mesothelium in pleural biopsy specimens. Immunostaining was enhanced by pepsin predigestion prior to the application of the primary antibody. Positivity occurred in 10/16 epithelial mesotheliomas, 9/19 biphasic mesotheliomas, 2/12 sarcomatous mesotheliomas but in none of 20 reactive pleura. Immunostaining was particularly intense in some of the biopsy specimens, which may be due to the rapidity with which these small pieces of tissue were fixed. In conclusion, this study suggests that p53 immunostaining can help to distinguish epithelial or biphasic mesothelioma from reactive mesothelial hyperplasia in formalin-fixed, paraffin-embedded pleural biopsy specimens.     

Usefulness of p16/CDKN2A fluorescence in situ hybridization and BAP1 immunohistochemistry for the diagnosis of biphasic mesothelioma

Malignant mesothelioma is a highly aggressive neoplasm, and the histologic subtype is one of the most reliable prognostic factors. Some biphasic mesotheliomas are difficult to distinguish from epithelioid mesotheliomas with atypical fibrous stroma. The aim of this study was to analyze p16/CDKN2A deletions in mesotheliomas by fluorescence in situ hybridization (FISH) and BAP1 immunohistochemistry to evaluate their potential role in the diagnosis of biphasic mesothelioma. We collected 38 cases of pleural mesotheliomas. The results of this study clearly distinguished 29 cases of biphasic mesothelioma from 9 cases of epithelioid mesothelioma. The proportion of biphasic mesotheliomas with homozygous deletions of p16/CDKN2A in total was 96.6% (28/29). Homozygous deletion of p16/CDKN2A was observed in 18 (94.7%) of 19 biphasic mesotheliomas with 100% concordance of the p16/CDKN2A deletion status between the epithelioid and sarcomatoid components in each case. Homozygous deletion of the p16/CDKN2A was observed in 7 (77.8%) of 9 epithelioid mesotheliomas but not in fibrous stroma. BAP1 loss was observed in 5 (38.5%) of 13 biphasic mesotheliomas and in both epithelioid and sarcomatoid components. BAP1 loss was observed in 5 (62.5%) of 8 epithelioid mesotheliomas but not in fibrous stroma. Homozygous deletion of p16/CDKN2A is common in biphasic mesotheliomas, and the analysis of only one component of mesothelioma is sufficient to show that the tumor is malignant. However, compared with histology alone, FISH analysis of the p16/CDKN2A status and BAP1 immunohistochemistry in the spindled mesothelium provide a more objective means to differentiate between biphasic mesothelioma and epithelioid mesothelioma with atypical stromal cells.     

Cadherins, catenins and APC in pleural malignant mesothelioma

Malignant mesothelioma is an aggressive disease of the pleura, and less commonly the peritoneum, with a very poor prognosis. The present study has examined the expression of cell adhesion molecules including cadherins, catenins, and APC in order to determine whether abnormal expression of components of the Wnt signalling pathway contribute to the variable phenotype of malignant mesothelioma. Sixty-three malignant mesotheliomas and nine cases of reactive mesothelial hyperplasia were analysed by immunohistochemistry for E-cadherin, N-cadherin, alpha-catenin, beta-catenin, and the C- and N-terminals of APC. In addition, DNA was extracted from formalin-fixed, paraffin wax blocks, and a 226 bp fragment of exon 3 of the beta-catenin gene was amplified, sequenced, and screened for activating mutations in the glycogen synthase kinase 3beta (GSK-3beta) phosphorylation targets. E-cadherin expression was detected in 48% of the epithelioid mesotheliomas but was observed in only 7% of sarcomatoid mesotheliomas. N-cadherin, alpha-catenin, beta-catenin, and the C- and N-terminals of APC did not show differential expression between the mesothelioma phenotypes. Abnormal nuclear localization of beta-catenin was demonstrated in 19% of mesotheliomas. Mutations of beta-catenin phosphorylation sites were not detected in any of the 62 mesotheliomas examined. Positive staining for the N-terminal of APC was seen in all of the cases of reactive mesothelial hyperplasia, as well as in all the mesotheliomas. Staining for the C-terminal of APC was negative in 23% mesotheliomas, despite being present in all the cases of reactive hyperplasia. The present study provides the first evidence that beta-catenin accumulates in the nucleus in malignant mesotheliomas. In addition, APC expression was altered in some mesotheliomas, suggesting that a truncated APC gene product may contribute to abnormal Wnt signalling and dysregulation of cell proliferation in malignant mesothelioma.     

Malignant mesothelioma: immunohistochemistry and DNA ploidy analysis as methods to differentiate mesothelioma from benign reactive mesothelial cell proliferation and adenocarcinoma in pleural and peritoneal effusions

OBJECTIVE: To determine whether malignant mesotheliomas can be differentiated from adenocarcinomas and benign reactive mesothelial cells in pleural and peritoneal fluids using immunohistochemical analysis in conjunction with DNA ploidy analysis. DESIGN: Sixteen cases of malignant mesothelioma, including epithelial, sarcomatous, and biphasic types, were collected. DNA analysis using flow cytometry and/or image analysis was performed on paraffin-embedded tissue from 15 of the mesothelioma cases, as well as on cytospin cell preparations from samples of pleural and peritoneal fluids from cases with either cytologically proven adenocarcinoma (seven cases) or benign reactive mesothelial cells (seven cases). Immunohistochemical studies were done in 15 mesotheliomas, 5 adenocarcinomas, and 4 benign reactive mesothelial cell effusions. RESULTS: All malignant mesotheliomas tested (100%) stained positively for prekeratin, whereas stains for carcinoembryonic antigen, B72.3, Leu-M1, and Ber-EP4 were negative. Stains vimentin, epithelial membrane antigen, and CA125 were positive in 75%, 75%, and 25% of cases tested, respectively. Benign reactive mesothelial cell cases stained similarly. Adenocarcinomas were more likely to react positively with B72.3, Ber-EP4, and carcinoembryonic antigen, and negatively with vimentin. DNA analysis showed that all benign cases were diploid, while all adenocarcinomas were nondiploid. Fifty-three percent of the malignant mesotheliomas were nondiploid. Sensitivity for detection of nondiploidy was greater for image analysis than for flow cytometry (100% vs 75%). CONCLUSIONS: B72.3, Ber-EP4, carcinoembryonic antigen, and vimentin are useful immunohistochemical markers in differentiating malignant mesotheliomas from adenocarcinomas, whereas immunohistochemistry does not reliably distinguish malignant from benign hyperplastic mesothelial cells. The addition of DNA ploidy studies is useful for differentiating the latter two groups.     

Praktische Differenzialdiagnose präneoplastischer Veränderungen der Pleura und früher mesothelialer Neoplasien

The morphological diagnosis of small mesothelial lesions in pleural biopsies is gaining importance in view of more aggressive, multimodal therapeutic options and of medicolegal aspects if a malignant mesothelioma is diagnosed. We present a light microscopically and immunohistochemically based morphological classification for the planning of further clinical follow-up procedures. A reactive mesothelial hyperplasia heals without scars. Mesothelial inclusions in pleuritic scars are common in recurrent pleuritis and must not be confused with an epithelioid component of a desmoplastic mesothelioma. In case of atypical mesothelial proliferations, further diagnostic procedures have to be performed to obtain a clear diagnosis of malignancy. Mesothelioma in situ is the first morphological step in neoplastic mesothelial changes, also with regard to medicolegal aspects for the unambiguous diagnosis of a mesothelioma. Early infiltrative growth is characteristic of so called early mesothelioma. A useful immunohistochemical panel for the differential diagnosis consists of anti-cytokeratin, Ck 5/6, calretinin, EMA and MiB-1, whereas the immunohistochemical detection of telomerase is not helpful.     

Benign pleural lesions and malignant mesothelioma

Summary In a series of eighteen diffuse malignant mesotheliomas, five cases were encountered in which thoracic surgery with benign nontumorous diagnosis preceded the development of a malignant mesothelioma by several years. The morphological findings in three of these five cases are compared with the morphology of the tumor specimens and an attempt is made to recognize the earliest possible malignant features. Crowding of mesothelial cells, their variability in size and nuclear hyperchromatism are pointed out as warning signs.In relation to these findings, the histogenetic significance of predominantly fibroproliferative versus epithelial-like pleural lesions is discussed. A histogenetic classification, based on the studies of eighteen diffuse malignant mesotheliomas, two benign fibrous mesotheliomas, one pleural fibrosarcoma, and numerous pleural plaques as well as reactive mesothelial lesions, is offered. The therapeutic aspects are mentioned.     

Atypical mesothelial hyperplasia associated with bronchogenic carcinoma.

Atypical mesothelial hyperplasia encountered in pleural fluid or in a pleural biopsy specimen raises the suspicion that one may be dealing with a diffuse malignant mesothelioma of the pleura. We studied eight cases with cytologic or histologic changes of mesothelial atypia thought to be suspicious for diffuse malignant mesothelioma. In each case, the hyperplasia was associated with a bronchogenic carcinoma in the lung subjacent to the mesothelial hyperplasia. Bronchogenic carcinoma should be added to the list of causes of atypical mesothelial hyperplasia. This combination of reactive and malignant processes should be appreciated, since pleural carcinomatosis and diffuse malignant mesothelioma must be separated for clinical and epidemiologic reasons.     

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.     

Scoring system for differential diagnosis of malignant mesothelioma and reactive mesothelial cells on cytology specimens

Cytology is the only useful tool in the detection of malignant mesothelioma (MM) at an early stage. No other methods, such as immunocytochemistry or electron microscopy, are available to distinguish MM from reactive mesothelial cells (RMC). Some objective analysis of cytology specimens is necessary. On the basis of our case review and cytological features described in previous articles, we developed a scoring system for malignant mesothelioma (SSMM) of effusion cytology to distinguish MM cells from RMC. Mesothelioma cells in effusions from 22 patients (20 pleural and 2 peritoneal mesotheliomas) were compared with RMC from 20 patients without obvious tumor cells and 50 effusions containing metastatic carcinoma cells. The SSMM is based on characteristic features of mesothelial and malignant cells. The total achievable score is 10 points: one point each is given for variety of cell size, cyanophilic cytoplasm with villosity/windows/bleb, sheet‐like arrangement, mirror‐ball‐like cell clusters, nuclear atypia, and cannibalism, respectively. Further two points each are ascribed for acidophilic large nucleoli and multinucleated cells with more than eight nuclei. The total score for each of the 22 mesotheliomas was more than 5 points. On the other hand, all RMC and the 50 metastatic carcinoma cases scored less than 3 points, aside from two cases that were treated with OK432. No single characteristic feature was observed to be consistent within the 22 mesotheliomas analyzed. Ancillary use of immunocytochemistry, such as podoplanin (D2‐40) and calretinin, supported the diagnostic accuracy of the SSMM. SSMM is useful for the differential diagnosis of MM. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.     

Differences in lectin binding of malignant pleural mesothelioma and adenocarcinoma of the lung.

In order to differentiate between malignant pleural mesothelioma and adenocarcinoma of the lung, the glycoconjugate profiles of 6 reactive mesothelial lesions, 23 mesotheliomas (17 epithelial, 1 desmoplastic, 2 biphasic, and 3 fibrous types), and 28 well-differentiated pulmonary adenocarcinomas were evaluated with the use of 8 lectins in addition to anti-carcinoembryonic, anti-keratin and anti-epithelial membrane antigen. Formalin-fixed, paraffin-embedded tissues were stained with the avidin-biotin peroxidase complex method. Reactions of wheat germ (WGA) and peanut (PNA) agglutinin with neuraminidase treatment lectins were positive in 5 of 6 (83%) and 3 of 6 (50%) cases, respectively, in reactive mesothelial lesions. Thirteen of 23 (57%) malignant mesotheliomas of the pleura showed a positive reaction for WGA and PNA with neuraminidase treatment; other lectins were low-positive, below 9%. In contrast, pulmonary adenocarcinomas showed positive reactions in 27 of 28 cases (96%) for PNA, 26 of 28 (93%) for Ricinus communis (RCA-I), 25 of 28 (89%) for WGA, and 22 of 28 (79%) for succinylated WGA (SucWGA). The findings suggest that malignant pleural mesothelioma and pulmonary adenocarcinoma have consistent and distinct glycoconjugate profiles, and that stains for RCA-I and SucWGA may be useful for differential diagnosis.     

D2-40: a reliable marker in the diagnosis of pleural mesothelioma.

OBJECTIVE: Malignant mesotheliomas of the pleura, peritoneum and pericardium can easily be confused with either metastatic adenocarcinomas or reactive pleural lesions. D2-40, a monoclonal antibody used as a marker for seminomatous germ cell tumours and lymphatic endothelial cells, was recently described in mesothelial cells and type I but not type II pneumocytes. METHOD: The immunoreactivities of D2-40 in 76 lung carcinomas of different histological types (adenocarcinomas, squamous cell, small cell, and bronchioloalveolar carcinomas) were compared with those of 36 pleural epithelioid and sarcomatoid mesotheliomas and 5 specimens of chronic pleuritis. RESULTS: While all 18 analysed epithelioid mesotheliomas displayed a strong membranous immunostaining, 18 sarcomatoid mesotheliomas showed no, or a merely faint, cytoplasmic signal, comparable with fibroblasts in chronic pleuritis. Out of all analysed lung carcinomas, 49 showed no immunoreactivity for D2-40 (64%), while the other 27 (36%) showed a focal weak to moderate and only cytoplasmic signal. CONCLUSIONS: We regard D2-40 as a valid marker in the differential diagnosis of epithelioid mesotheliomas versus pulmonary adenocarcinomas. However, this marker may not properly label sarcomatoid mesotheliomas or distinguish them from reactive pleural lesions.