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

Immunocytochemistry of effusion fluids: Introduction to SCIP approach

Due to the remarkably wide morphologic spectrum of reactive mesothelial cells, some of the effusion fluids may be difficult to interpret with objective certainty by cytomorphology alone. Cytomorphology of well to moderately differentiated adenocarcinomas (responsible for the bulk of malignant effusions) may overlap with floridly reactive mesothelial cells. Even mesotheliomas including diffuse malignant epithelioid mesothelioma, are usually cytomorphologically bland without unequivocal features of malignancy. The intensity of challenge depends on the interpreter's training or experience level, institutional demographics of patients (such as type of prevalent diseases, predominant sex and age group), technical support, and quality of cytopreparatory processing. In general immunocytochemistry is valuable adjunct to facilitate objective interpretation with or without other ancillary techniques as indicated. An increasing number of immunomarkers is further refining the contribution of immunohistochemistry to this field. However, application of immunohistochemistry to effusion fluids is relatively challenging because of many variables. Multiple factors such as delay after specimen collection, specimen processing related factors including fixation and storage; ambient conditions under which paraffin blocks are archived (for retrospective testing); antigen retrieval method; duration of antigen retrieval step; antibody clone and dilution; and antibody application time are identical to application of immunohistochemistry in other areas. The significant challenge related to the potential compromization of the immunoreactivity pattern due to exposure to non-formalin fixatives / reagents is also applicable to effusion fluid specimens. The immunoreactivity results would be compared and corelated with cumulative metadata based on the reported studies performed and validated on formalin-fixed paraffin-embedded tissue sections. Deviating from such protocols may lead to suboptimal results, which is not uncommon in clinical practice with potential compromization of patient care and related liability. Because of this, it is critical to perform immunocytochemistry on formalin-fixed cell-block sections only. In addition, unless the interpretation criteria for immunohistochemical evaluation of effusion fluids are not modified specifically, it may not be productive in resolving some challenging cases. However, this aspect is not well elaborated in the literature. A basic and critical challenge is finding and locating the cells of interest in cell-block sections of effusion fluids. A unique approach is to choose a fundamental immunopanel which highlight the mesothelial and inflammatory cells in reactive effusion fluids to create the basic map. This allows detection of a 'second-foreign' population which can be immunocharacterized further with the help of subtractive coordinate immunoreactivity pattern (SCIP) approach elaborated here.

Immunochemistry in the work-up of mesothelioma and its differential diagnosis and mimickers

The differential diagnosis in cellular effusions with cytological atypia often includes malignant mesothelioma (MM), reactive mesothelial proliferation, and malignancies of metastatic origin, particularly carcinomas. The International Reporting System for Serous Fluid recently established guidelines for reporting MM. In conjunction with the cytomorphologic evaluation, the role of immunochemistry (IC) was emphasized as a very useful tool in the workup of serous fluids, especially with the availability of novel markers. Utilizing a panel of markers, IC allows the characterization of the cells, whether mesothelial or not, and when mesothelial origin is established, IC can frequently assist in delineating its benign or malignant nature. IC can also confirm metastatic disease, allowing the identification of the primary origin in most cases. This review summarizes the current status of IC and its role in the diagnosis of MM and its differential diagnosis in serous fluids.

Value of claudin-4 immunostaining in the diagnosis of mesothelioma

Claudin-4 (CL-4) is a tight junction-associated protein that is expressed in most epithelial cells but absent in mesothelial cells. The purpose of this study is to evaluate the utility of CL-4 immunostaining for assisting in the differential diagnosis of mesothelioma. Sixty mesotheliomas (40 epithelioid, 10 biphasic, and 10 sarcomatoid), 185 carcinomas of different origins that can potentially be confused with mesotheliomas, 37 soft-tissue sarcomas, and 5 melanomas were investigated for CL-4 expression. All 60 mesotheliomas were CL-4 negative. In contrast, 169 (91%) of 185 carcinomas expressed this marker. Five of 8 desmoplastic small round cell tumors and the epithelial component of all 5 biphasic synovial sarcomas were CL-4 positive, whereas none of the remaining soft-tissue sarcomas or melanomas expressed this marker. It is concluded that CL-4 is a highly specific and sensitive immunohistochemical marker for assisting in distinguishing epithelioid mesotheliomas from metastatic carcinomas to the serosal membranes.

Application of immunohistochemistry in the diagnosis of epithelioid mesothelioma: a review and update

A large number of immunohistochemical markers that can assist in the differential diagnosis of epithelioid mesotheliomas are currently available. Because these markers are expressed differently in the various types of carcinomas that can metastasize to the serosal membranes and can potentially be confused with epithelioid mesothelioma, their selection for inclusion in a diagnostic panel largely depends on the differential diagnosis, as well as on which ones work the best in a given laboratory. Traditionally, the panels used in the differential diagnosis of epithelioid mesothelioma have consisted of a combination of positive mesothelioma markers and broad-spectrum carcinoma markers. At present, a wide variety of organ-associated carcinoma markers such as thyroid transcription factor-1 and napsin A for the lung, PAX 8 and PAX 2 for the kidney, and Müllerian-derived tumors; gross cystic disease fluid protein-15 and mammaglobin for the breast; and CDX2 for intestinal differentiation are available, which can assist in establishing the site of origin of an adenocarcinoma when included in a diagnostic panel. This article provides updated information on the composition of the panels of markers recommended in the various differential diagnoses.

Immunocytochemical panel for distinguishing between adenocarcinomas and reactive mesothelial cells in effusion cell blocks

The aim of our study was to determine the value of a panel that consisted of one epithelial marker (MOC-31) and two mesothelial markers (D2-40 and calretinin) for distinguishing between reactive mesothelial cells (RMCs) and adenocarcinomas (ACs) in effusion fluids. A total of 118 cell block specimens from pleural and peritoneal effusions, including 88 ACs and 30 benign effusions with RMCs were stained with antibodies against MOC-31, D2-40, and calretinin. MOC-31 membranous activity was observed in all samples from ACs, regardless of the primary tumor site. All benign effusion samples with RMCs were negative for MOC-31. All benign effusion samples with RMCs exhibited membranous staining for D2-40, and one AC case had focal reactivity for D2-40. Almost all benign effusions reacted positively with calretinin. Staining was noted in both the cytoplasm and the nucleus in the majority of cases. Scattered tumor cells had weak calretinin positivity in two AC cases. Background RMCs in AC effusions were consistently positive for D2-40 and calretinin. In general, D2-40 identified more RMCs than calretinin. The staining combination of positive for MOC-31 and negative for D2-40 or calretinin were 100% specific and 99% sensitive for ACs. Our data suggest that immunohistochemical studies performed on cell blocks with MOC-31, D2-40, and calretinin were useful in the differentiation between ACs and RMCs. D2-40 was a more sensitive marker for RMCs than calretinin.

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.

What are the current best immunohistochemical markers for the diagnosis of epithelioid mesothelioma? A review and update

Numerous immunohistochemical markers that can assist in the diagnosis of epithelioid mesotheliomas, some of which have only recently been recognized, are currently available. Because the various types of carcinomas express these markers differently, their selection for inclusion in a diagnostic panel can vary according to the differential diagnosis. This article provides a critical review of all of the information that is presently available on those markers that are believed to have the greatest potential for assisting in distinguishing between epithelioid mesotheliomas and those carcinomas with which they are most likely to be confused. Information is also provided regarding the panels of immunohistochemical markers that are, at present, recommended in these differential diagnoses.

The high post-test probability of a cytological examination renders further investigations to establish a diagnosis of epithelial malignant pleural mesothelioma redundant

The aim of the study was to establish in a prospective and blinded manner the diagnostic yield of morphology, immunocytochemistry (ICH) and electron microscopy (EM) in the cytological analysis of malignant pleural mesothelioma (MPM). Pleural fluid from consecutive patients, 14 with a histologically proven MPM, 12 with a malignant pleuritis due to adenocarcinoma (AC), and 13 with a reactive pleural effusion (RM), was separately analyzed. Smears were incubated with monoclonal antibodies (Tag72, Ber-Ep4, anti-CEA, EMA). These were considered suggestive for MPM when only EMA stained positive, for AC when three out of four markers stained positive, and for RM when no marker stained positive. The post-test probability of the morphological, ICH, and EM analysis were 92, 100, 92% or MPM, 91, 100, 86% for AC, and 88, 88, 90% for RM, respectively. We concluded that the high post-test probability of a combined morphological and ICH diagnosis of MPM warrants to cease further diagnostic procedures in these patients. Electron microscopy did not add to accuracy of diagnosis.

Use of mesothelin as a marker for mesothelial cells in cytologic specimens

Immunocytochemistry is often employed for the distinction between mesothelial cells and adenocarcinoma. Mesothelin has recently been reported to be expressed in reactive mesothelial cells and epithelioid mesotheliomas. The objective of this study is to determine the utility of mesothelin as marker for mesothelial cells in cytologic preparations. Thirty cell blocks were retrieved from the archives and immunostained with monoclonal antibody directed against mesothelin and calretinin. Heat-induced epitope retrieval technique was employed, and the immunostaining was accomplished using an automated stainer. These tissue blocks were from 35 patients (17 females and 18 males) with a median age of 64 years. Nine were benign effusions, 11 mesotheliomas, and 18 metastatic adenocarcinomas. The presence of any immunoreactivity, irrespective of level of intensity or percentage of cells, was considered positive for mesothelin expression. Follow up included correlation with pathology materials obtained at surgery and review of medical records. Mesothelin staining was positive in 7/9 benign cases, 8/11 mesotheliomas, and 8/18 adenocarcinomas. The difference of mesothelin expression between mesothelial cells and adenocarcinoma was statistically significant. For calretinin, all cases, except 2 malignant mesotheliomas and 3 adenocarcinomas, showed positive staining with calretinin. As a marker for mesothelial cells, the sensitivity and specificity of mesothelin were 73% and 55%, respectively, and the sensitivity and specificity of calretinin were 95% and 86%, respectively. Therefore, mesothelin is not a sensitive or a specific marker for mesothelial cells in cytologic specimens when compared with calretinin.

Sensitivity and specificity of immunohistochemical markers used in the diagnosis of epithelioid mesothelioma: a detailed systematic analysis using published data

AIMS

Immunohistochemistry is frequently employed to aid the distinction between mesothelioma and pulmonary adenocarcinoma metastatic to the pleura, but there is uncertainty as to which antibodies are most useful. We analysed published data in order to establish sensitivity and specificity of antibodies used to distinguish between these tumours with a view to defining the most appropriate immunohistochemical panel to use when faced with this diagnostic problem.

METHODS AND RESULTS

A systematic analysis of the results of 88 published papers comparing immunohistochemical staining of a panel of antibodies in mesothelioma with epithelioid areas, and pulmonary adenocarcinoma metastatic to the pleura. Results for a total of 15 antibodies were analysed and expressed in terms of sensitivity and specificity. The most sensitive antibodies for identifying pulmonary adenocarcinoma were MOC-31 and BG8 (both 93%), whilst the most specific were monoclonal CEA (97%) and TTF-1 (100%). The most sensitive antibodies to identify epithelioid mesothelioma were CK5/6 (83%) and HBME-1 (85%). The most specific antibodies were CK5/6 (85%) and WT1 (96%).

CONCLUSIONS

No single antibody is able to differentiate reliably between these two tumours. The use of a small panel of antibodies with a high combined sensitivity and specificity is recommended.

Monoclonal antibody MOC-31 reactivity as a marker for adenocarcinoma in cytologic preparations

BACKGROUND

It has been shown previously that detection of the epithelial membrane antigen using the mouse monoclonal antibody MOC-31 has diagnostic utility in the distinction between mesothelioma and metastatic carcinoma in body fluids. The current immunohistochemical study confirmed the effectiveness of MOC-31 as a marker for adenocarcinoma from a broad range of primary sites in body fluid cytology prepared as paraffin sections of cell blocks.

METHODS

The authors evaluated 112 cell blocks for MOC-31 immunoreactivity, including 17 mesotheliomas, 86 metastatic adenocarcinomas from various sites, and 9 control fluids from patients with nonneoplastic conditions.

RESULTS

Membranous reactivity for MOC-31 was observed in 86 of 86 samples (100%) of metastatic adenocarcinoma, regardless of the specific primary site. Sixteen of 17 mesothelioma samples were negative. In all but 1 sample of adenocarcinoma, > 90% of tumor cells present showed reactivity, and the staining intensity consistently was strong. Staining of scattered, morphologically benign mesothelial cells was observed in nine samples but did not interfere with interpretation.

CONCLUSIONS

On the basis of the staining profile, MOC-31 represented an effective marker for metastatic carcinoma in cell block preparations and may aid in distinguishing between benign and malignant mesothelial cells in these tumors.

Ber-EP4 and anti-calretinin antibodies: a useful combination for differential diagnosis of various histological types of ovarian cancer cells and mesothelial cells

The differential diagnosis between reactive mesothelial cells and ovarian carcinoma cells is often difficult in cytologic specimens. Immunocytochemical procedures have been utilized in assisting this differential diagnosis, with limitations. Furthermore, previous studies examined only serous type but not other histological types of ovarian carcinoma cases. Therefore, we evaluated the practical value of various epithelial and mesothelial markers in differential diagnosis of these two types of cells. Various types of ovarian carcinoma (serous, n = 22; mucinous, n = 10; endometrioid, n = 7; clear cell, n = 10) and benign mesothelial tissues (n = 15) were studied by immunohistochemistry. We then studied effective panels of antibodies by immunohistochemistry in 43 cytologic specimens of ascites or peritoneal lavage fluid consisting of 20 reactive mesothelium and 23 adenocarcinomas of the ovary. In the tissue specimens, Ber-EP4, a monoclonal antibody of epithelial antigen, and a polyclonal antibody against calretinin, which is expressed in mesothelium, are used in differentiating reactive mesothelial cells from ovarian carcinoma. In cytologic specimens, the sensitivity and specificity of Ber-EP4 were 100% and 90%, respectively. The sensitivity and specificity of the anti-calretinin antibody were 90% and 91%, respectively. Using multiple regression analysis, the correlation coefficient between epithelial antigen and calretinin reactivity was r = 0.938, with a significance level of p < 0.0001. In conclusion, the combined immunostaining of cytologic specimens for Ber-EP4 and the anti-calretinin antibody is helpful for the differential diagnosis between mesothelial cells and not only serous type, but also mucinous, endometrioid and clear cell types of ovarian cancer cells.

Serous effusions: diagnosis of malignancy beyond cytomorphology. An analytic review

In this brief review, the role of various ancillary techniques to detect malignancy in effusion fluid are evaluated and discussed. The data were collected from a large number of research articles published in various medical journals. The role of these techniques to increase the diagnostic accuracy in serous effusions is emphasised.

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 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.

Use of a panel of markers in the differential diagnosis of adenocarcinoma and reactive mesothelial cells in fluid cytology

To evaluate the use of a panel of markers to differentiate adenocarcinoma and the reactive/inflammatory process in fluid cytology, we stained 29 formalin-fixed, paraffin-embedded cell blocks of effusion fluid from patients with metastatic adenocarcinoma and 24 cell blocks from patients with benign effusion with mucicarmine and antibodies to carcinoembryonic antigen (CEA), B72.3, and calretinin. Positive staining with CEA, B72.3, and mucicarmine was seen in 22 (76%), 20 (69%), and 18 (62%) adenocarcinoma cases, respectively. All except 1 adenocarcinoma was negative for calretinin. No benign cases were positive for B72.3 and mucicarmine. In 1 benign case, scattered epithelial cells demonstrated weak positivity for CEA. The majority of combinations were 100% specific for adenocarcinoma. The highest sensitivity (86%) for adenocarcinomas was achieved with the staining combination of negative for calretinin and positive for any adenocarcinoma marker (CEA, B72.3, or mucicarmine). The use of a panel of markers that recognize adenocarcinoma and mesothelial cells is useful in the differential diagnosis between metastatic adenocarcinoma and the reactive/inflammatory process. The profile of positive staining with at least one of the adenocarcinoma markers and negative calretinin staining is highly specific and sensitive for identifying adenocarcinoma in fluid cytology.

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.

Combined use of novel epithelial (MOC-31) and mesothelial (HBME-1) immunohistochemical markers for optimal first line diagnostic distinction between mesothelioma and metastatic carcinoma in pleura

AIMS

To determine the value of immunohistochemistry in differentiation of malignant pleural mesothelioma from carcinoma in a pleural biopsy we optimized a double panel of MOC-31 and HBME-1 and compared the results with others from the literature.

METHODS AND RESULTS

A multi-antibody panel was applied to biopsy samples from 44 cases of malignant pleural mesothelioma and 23 cases of carcinoma metastatic to the pleura. We used monoclonal antibodies against keratins, epithelial membrane antigen (EMA), epithelial antigen Ber-EP4, carcinoembryonic antigen (CEA), tumour-associated glycoprotein (B72.3), LeuM1, vimentin, desmin, epithelial related antigen (MOC-31) and mesothelial cell (HBME-1). Positivity for MOC-31 and Ber-EP4 was found to have the highest nosologic sensitivity (94.1% and 84.6%, respectively) and specificity (86.3% both antibodies) for carcinoma. Positive staining for HBME-1 and vimentin had the highest sensitivity (90.9% and 100%, respectively) and specificity (91.3% and 60%, respectively) for mesothelioma. A two-marker antibody panel with HBME-1 and MOC-31 was the most efficient for the distinction between carcinoma and malignant pleural mesothelioma.

CONCLUSION

A combination of MOC-31 (an anti- epithelial marker) and HBME-1 (an anti-mesothelial marker) has a diagnostic efficiency of 76.1% for the distinction between carcinoma and mesothelioma in pleura.

Image analysis and flow cytometric DNA studies of benign and malignant body cavity fluids: reappraisal of the role of current methods in the differential diagnosis of reactive versus malignant conditions

Cytologic examination of body fluids is commonly performed in the clinical laboratory. Determination of the presence of malignancy may sometimes be difficult. In this study, we prospectively studied 60 body fluids with a panel of antibodies, including MOC-31, epithelial membrane antigen, carcinoembryonic antigen, B72.3, keratin, desmin, and CA-125. DNA and S-phase studies were performed both by flow cytometry and image analysis. Thirty-seven fluids were classified as benign and 23 were classified as malignant. The sensitivity of the antibodies for identification of carcinoma in descending order of percentage detection rate were MOC-31 (95%), epithelial membrane antigen (93%), B72.3 (84%), and carcinoembryonic antigen (80%). Desmin stained mesothelial cells in all cases. CA-125 gave similar results but was less specific. Flow cytometry detected 14 of 20 malignant fluids and image analysis 17 of 23 by identifying an aneuploid population. Benign reactive mesothelial cells were not aneuploid. Tetraploidy due to reactive mesothelial cells was found in 9 of 37 body fluids. Their S-phase fraction was low (average, 3.2%). Tetraploidy in malignant cells was distinguished from the reactive mesothelial cells by high S-phase (average, 25.95). S-phase had some use as a discriminating factor, because no benign reactive cases had more than 17%. However, 7 of 23 malignant cases had a value below 17%. DNA analysis by image was more sensitive and specific than flow. Either may be used when immunocytochemistry is nondiagnostic or cannot be performed.

Calretinin staining pattern aids in the differentiation of mesothelioma from adenocarcinoma in serous effusions

BACKGROUND

The differentiation between malignant mesothelioma and adenocarcinoma based on morphology alone can be a diagnostic challenge. The majority of the available antibodies recognize molecules expressed by adenocarcinoma whereas to the authors' knowledge specific markers for mesothelial cells are lacking. Calretinin, a calcium-binding protein, has been reported to be a selective marker for mesothelioma and largely is absent from adenocarcinoma on histologic material. The results with cytologic preparations have been inconsistent.

METHODS

To evaluate the specificity of calretinin in differentiating mesothelioma from adenocarcinoma in cytologic preparations, 21 paraffin embedded cells blocks of serous effusions from 15 patients with metastatic adenocarcinoma and 16 cell blocks from 9 patients with malignant mesothelioma were stained with a monoclonal antibody against calretinin. The immunoreactivity was evaluated blindly by two observers. Positive staining was defined as nuclear and cytoplasmic staining with or without intense membranous decoration. The former resulted in a characteristic "fried egg" appearance.

RESULTS

Calretinin staining was positive in all but 2 cases of mesothelioma (14 of 16 cases; 87.5%). The latter contained predominantly spindle-shaped neoplastic mesothelial cells in the cell block preparations. All adenocarcinoma specimens were classified as negative for calretinin staining; 9 (42.9%) lacked any immunoreactivity and 12 (57.1%) showed weak, sparse, coarse, granular cytoplasmic staining without nuclear or membranous staining. Benign reactive mesothelial cells, when observed in association with adenocarcinoma, also showed the characteristic "fried egg" appearance. The difference in the staining pattern of calretinin between cells of mesothelial origin and adenocarcinoma cells was statistically significant.

CONCLUSIONS

Calretinin is a useful marker in differentiating mesothelioma of the epithelial type from adenocarcinoma in serous effusions. The "fried-egg" appearance or cytoplasmic and nuclear staining pattern is characteristic of cells of mesothelial origin.

HBME-1, MOC-31, WT1 and calretinin: an assessment of recently described markers for mesothelioma and adenocarcinoma

AIMS

To evaluate HBME-1, WT1, calretinin and MOC-31 in the differential diagnosis of pleural mesothelioma and adenocarcinoma of the lung.

METHODS AND RESULTS

Paraffin-embedded formalin-fixed blocks from six reactive pleuras, 42 mesotheliomas and 40 adenocarcinomas were used. Sections were stained for Leu-M1, HBME-1, calretinin, WT1 and MOC-31. Leu-M1 was positive or equivocal in 34% of mesotheliomas and in 78% of adenocarcinomas; reactive pleuras were all negative. HBME-1 was positive or equivocal in 76% of mesotheliomas and in 73% of adenocarcinomas; five reactive pleuras were positive. Calretinin was positive or equivocal in 92% of mesotheliomas and in 73% of adenocarcinomas; two reactive pleura were equivocal and four were positive. WT1 was positive or equivocal in 72% of mesotheliomas (excluding autopsy cases) and in 20% of adenocarcinomas; all reactive pleuras were positive. MOC-31 was positive or equivocal in 5% of mesotheliomas and in 90% of adenocarcinomas; all reactive pleuras were negative. The reaction with Leu-M1 was graded as equivocal in 25% of the adenocarcinomas. All 24 of the autopsy cases of mesothelioma were negative for WT1 and in many operative specimens only the periphery was stained.

CONCLUSIONS

Neither calretinin nor HBME-1 are sufficiently discriminatory to be of use, even as members of a panel of antibodies. WT1 shows some promise, but it cannot be used on autopsy material. The utility of MOC-31 is confirmed, and outperforms Leu-M1.

MOC-31 aids in the differentiation between adenocarcinoma and reactive mesothelial cells

BACKGROUND

Evaluation of effusion specimens for the presence of adenocarcinoma often is complicated by the presence of reactive mesothelial cells that can mimic adenocarcinoma. Ancillary studies, in particular immunohistochemistry, can be helpful in making this distinction. MOC-31 is an antibody that recently was reported to be useful in distinguishing adenocarcinoma from mesothelioma in tissue specimens. In this study we examined the utility of this antibody in pleural effusions.

METHODS

Eighty-nine archival, formalin fixed, paraffin embedded cell blocks representing 59 adenocarcinomas, 12 other neoplasms (including 6 mesotheliomas), and 18 reactive effusions were retrieved. After protease digestion, recut slides were immunostained with the MOC-31 antibody utilizing a modified avidin-biotin complex technique. Only membrane-based reactivity was considered as positive.

RESULTS

In two adenocarcinomas there was insufficient material remaining in the cell block. Among the 57 remaining cases, reactivity was observed in 54 cases. Reactivity also was observed in one of six mesotheliomas and one small cell carcinoma. The remaining cases, including all 18 reactive effusions, were nonreactive. In distinguishing adenocarcinoma from reactive mesothelial cells, the presence of MOC-31 reactivity was found to be 95% sensitive and 100% specific with a positive predictive value of 100% and a negative predictive value of 95%.

CONCLUSIONS

MOC-31 is useful in differentiating between adenocarcinoma and reactive mesothelial cells in pleural effusion specimens. Cancer (Cancer Cytopathol)

The value of anti-calretinin antibody in the differential diagnosis of normal and reactive mesothelia versus metastatic tumors in effusion cytology

In effusion cytology the distinction of reactive mesothelia from metastatic carcinoma cells may be a diagnostic challenge. Immunocytochemistry using antibodies suitable to detect epithelial cells must be considered carefully due to limited sensitivity and specificity of these antibodies. Efficient results in histological differential diagnosis of malignant mesothelioma versus lung-adenocarcinoma applying a novel antiserum against the calcium binding protein calretinin inspirated us to investigate the value of anti-calretinin antibody in effusion cytology combined with an epithelial marker. Cytoslides prepared by cytocentrifugation from 42 malignant and 65 reactive effusion specimens were immunostained using antibodies against calretinin and the epithelial marker Ber-EP4. Positive immunoreaction for calretinin in normal and reactive mesothelial cells was noted in 93% of the cases, whereas immunoreaction for calretinin was completely negative in the metastatic cells in 95% of the malignant effusions. Metastatic carcinoma cells were detected with anti-Ber-EP4 in 83% of malignant effusions. Non-specific positive reactions for Ber-EP4 in single mesothelial cells were observed in 16% of all cases and, moreover, frequently with macrophages or neutrophilic granulocytes. Our results demonstrate high sensitivity and specificity of anti-calretinin antibody for mesothelial cells in effusion specimens. They support its application to improve the diagnostic reliability of epithelial markers, especially because anti-calretinin antibody could be helpful in the assessment of false positive and false negative reactions of epithelial markers.

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.

Utility of the antibodies CA 19-9, HBME-1, and thrombomodulin in the diagnosis of malignant mesothelioma and adenocarcinoma in cytology

BACKGROUND

The distinction between malignant mesothelioma (MM) and adenocarcinoma (ACA) in cytologic specimens frequently is difficult, often requiring immunocytochemistry to support the diagnosis. Recent reports have proposed the utilization of antibodies to mesothelial cell clone HBME-1 and thrombomodulin (TM), because they are immunoreactive in MM and less commonly reactive in ACA. Immunoreactivity for the monoclonal antibody CA 19-9 has been observed in many ACAs and reportedly is absent in MM.

METHODS

In this study, immunostaining was performed on formalin fixed, paraffin embedded cell blocks from effusions or fine-needle aspirations using the avidin-biotin-peroxidase method. Thirty-eight MMs and 49 ACAs were tested using antibodies to CA 19-9, HBME-1, and TM.

RESULTS

Anti-CA 19-9 stained only 1 of the 37 cases of MM tested (3%), but stained 24 of the 49 cases of ACA (49%). Anti-HBME-1 stained 34 of 38 cases of MM (89%), and 28 of 43 cases of ACA tested (65%). Anti-TM stained 24 of 36 cases of MM (67%), and 21 of 40 cases of ACA tested (53%).

CONCLUSIONS

CA 19-9 has utility as part of an immunocytochemical panel for distinguishing ACA from MM, because a positive staining reaction would make the diagnosis of MM unlikely. Although HBME-1 and TM can identify MM positively, each frequently is detected in ACA, thus limiting the utility of these antibodies in cytologic specimens.

Immunohistochemical evidence of the mesothelial histogenesis of a uterine adenomatoid tumor

We present rare case of a uterine adenomatoid tumor. In order to characterize the diversity of immunoreactive antigens associated with mesothelial differentiation, we immunohistochemically examined the tumor's epithelioid and myofibromatoid components, as well as the biphasic pattern of its adenomatoid changes. Immunostaining of tumor cells was positive for high- and low-molecular-weight cytokeratins and vimentin. Specific immunoreactions with antibodies against desmin, alpha-actin, and the S-100 protein also were observed. The present adenomatoid tumor can be explained in terms of various transformations and typical alterations in mesothelioma cells: (1) the mesothelial cells had differentiated to epithelial and stromal components, concomitant with the presence of predominant reactive foci; (2) intermediate cells expressed different types of cytoskeletal intermediate filament proteins (IMPs); and (3) the patterns of fibromatoid and leiomyoid differentiation resembled those of a benign mesothelioma of the ovarian or oviductal peritoneum. Our immunohistochemical investigations indicated that the present tumor exhibited the histogenesis of a true mesothelioma, an adenomatoid mesothelioma.

E-cadherin and calretinin: a useful combination of immunochemical markers for differentiation between mesothelioma and metastatic adenocarcinoma

AIMS

To assess the diagnostic accuracy of combinations of antibodies in the differential diagnosis of metastatic carcinomas and mesotheliomas in pleural lesions.

METHODS AND RESULTS

The specificity and sensitivity of the commercially available antibodies Ber-EP4, MOC-31, CEA, B72.3, CD15, E-cadherin and calretinin were evaluated using an indirect immunoperoxidase staining technique. This technique was applied to formalin-fixed, paraffin-embedded tissue blocks of pleural lesions. Twenty-one patients with metastatic carcinoma (MC) and 20 patients with malignant mesothelioma (MM) were included. The combination E-cadherin/calretinin had the highest specificity (MC 100% and MM 91%) and sensitivity (MM 100% and MC 91%) considering both categories of tumours.

CONCLUSIONS

The combination of E-cadherin/calretinin appears to be a suitable panel for distinguishing metastatic carcinomas and mesotheliomas in pleural lesions. The additional value of other markers is limited.

Value of the MOC-31 monoclonal antibody in differentiating epithelial pleural mesothelioma from lung adenocarcinoma

MOC-31 is a monoclonal antibody that has recently become commercially available that recognizes an epithelial-associated, transmembrane glycoprotein often expressed in epithelial tumors. Although some authors have indicated that MOC-31 immunostaining can assist in distinguishing epithelial mesotheliomas from metastatic adenocarcinomas to the pleura, others have concluded that this marker has no value in separating these conditions. To determine whether MOC-31 immunostaining can assist in discriminating epithelial pleural mesothelioma from lung adenocarcinoma or from other carcinomas metastatic to the pleura, 38 epithelial pleural mesotheliomas, 40 pulmonary adenocarcinomas, 55 nonpulmonary adenocarcinomas, six squamous cell carcinomas of the lung (SCCLs), three small-cell lung carcinomas (SCLCs), 19 bronchial carcinoids (BCs), and 15 transitional cell carcinomas (TCCs) were studied. Reactivity was obtained in two (5%) of the mesotheliomas, in all 40 (100%) pulmonary adenocarcinomas, in 45 (82%) nonpulmonary adenocarcinomas, in six (100%) SCCLs, three (100%) SCLCs, 15 (83%) BCs, and 10 (67%) TCCs. The staining in the two positive mesotheliomas was restricted to a few cells, in contrast to the pulmonary adenocarcinomas and most of the other carcinomas where it was often strong and diffuse. It is concluded that MOC-31 can be useful in separating epithelial pleural mesothelioma from pulmonary adenocarcinoma or from other epithelial malignancies involving the pleura.

The use of epithelial membrane antigen and silver-stained nucleolar organizer regions testing in the differential diagnosis of mesothelioma from benign reactive mesothelioses

BACKGROUND

The accurate diagnosis of pleural lesions obtained from small closed biopsy is difficult. As yet there is no single reliable test to distinguish between malignant and benign mesothelial tissue.

METHODS

Immunostaining of epithelial membrane antigen (EMA) and the quantitation of silver stained nucleolar organizer regions (AgNORs) each were applied to benign and malignant histologic sections of pleural and peritoneal biopsies. The usefulness of these stains was tested both individually and in combination in the diagnosis of epithelial malignant mesothelioma.

RESULTS

One hundred and three of the 141 malignant lesions (73%) were immunoreactive for EMA but only 3 of the 73 benign lesions (4%) reacted equivocally, and none positively. The average count of AgNORs/cell in malignant lesions (n = 80) was elevated compared with benign cases (n = 26), but a significant overlap was exhibited in the AgNOR count and this form of analysis was considered to be of little value in distinguishing benign from malignant mesothelial processes. Much less overlap was observed when the average AgNOR area was measured. By using the maximum benign AgNOR area of 0.6677 microm2 as the upper threshold, 51 cases (63.8%) were identified as malignant; the test demonstrated 100% specificity and 63.8% sensitivity. By combining the EMA and AgNOR results, 76 of 80 of the malignant mesothelioma cases (95%) tested positive for at least 1 of the tests with no false-positive results identified.

CONCLUSIONS

This study confirms the usefulness of EMA in diagnosing malignant and benign mesothelial lesions, and demonstrates the enhanced diagnostic value of combining EMA immunoreaction with the average area of AgNOR per cell, thereby increasing sensitivity in the diagnosis of epithelial malignant mesothelioma.

The immunohistochemical diagnostic panel for epithelial mesothelioma: a reevaluation after heat-induced epitope retrieval

The immunohistochemical diagnosis between epithelial mesothelioma and adenocarcinoma is currently based on the use of a panel of antibodies to adenocarcinoma-associated antigens and a few antibodies to mesothelial-associated antigens. Since the introduction of epitope retrieval methods, the sensitivity of many antibodies has been enhanced. Thus, a reevaluation of the mesothelioma/adenocarcinoma diagnostic panel becomes necessary. We studied 268 paraffin-embedded formalin-fixed tumor samples that included 57 epithelial mesotheliomas and 211 adenocarcinomas of various origins, comparing an extensive antibody panel with and without heat-induced epitope retrieval (HIER). Marked increase in the sensitivity of several antibodies, with no loss of specificity, was found when HIER was used. After statistical analysis, the antibodies to the epithelial glycoproteins carcinoembryonic antigen, BerEp4, and Bg8 emerged as the best discriminators between adenocarcinoma and epithelial mesothelioma within the entire panel. The mesothelium-associated antibodies, HBME-1, calretinin, and thrombomodulin were less sensitive and less specific than the former, although they were found to be useful on certain cases. Antibodies to cytokeratins and vimentin, although of minor diagnostic value in this context, may be helpful to evaluate the quality of antigen preservation. This study confirms the value of immunohistochemistry to accurately distinguish mesothelioma from adenocarcinoma when an antibody panel approach is used. The addition of heat-induced epitope retrieval methods increases the effectiveness of the procedure and is recommended for most of the antibody panel members.

Newly marketed tissue markers for malignant mesothelioma: immunoreactivity of rabbit AMAD-2 antiserum compared with monoclonal antibody HBME-1 and a review of the literature on so-called antimesothelioma antibodies

A complementary DNA (cDNA) library was constructed from a human malignant mesothelioma (MM) cell line and a cDNA fragment encoding for a cytoplasmic mesothelial protein recognized by the polyclonal antibody AMAD-1 was then cloned and expressed in Escherichia coli. The purified recombinant protein was used to raise a novel antibody, named AMAD-2, in rabbits. This antibody reacted with normal mesothelium and most MM (15 of 17) on paraffin sections and featured a cytoplasmic labeling. Conversely, AMAD-2 immunostaining of normal and tumor tissues from body sites other than serosal membranes was limited with respect to the proportion of positive specimens and usually less conspicuous than in MM. AMAD-2 immunoreactivity was subsequently compared with staining for HBME-1, another newly marketed antimesothelial monoclonal antibody, concerning the ability to distinguish pleural MM from metastatic pleural tumors of epithelial type. A granular cytoplasmic immunoreactivity for AMAD-2 was present in 50% or more of tumor cells in all 84 MM, regardless of histological type, but also in 3 (7%) of 42 pleural metastases, albeit only focally. HBME-1 was shown in 63 of 66 epithelial MM and in the epithelial component of all 8 mixed MM, with a prevailingly membranous pattern, usually homogeneous and strong, whereas none of the 10 sarcomatous MM was positive. HBME-1 was also expressed in 6 (14%) of 42 pleural metastases in a cytoplasmic or membranous pattern. Compared with HBME-1, AMAD-2 showed a higher degree of specificity and sensitivity for MM. AMAD-2 still proved to be superior to HBME-1, also when sarcomatoid MM were excluded from the assessment. This finding supports the view that AMAD-2 is an antibody highly, although not entirely, specific for the mesothelial lineage, whereas HBME-1 is probably a cell marker more closely related to the epithelial differentiation of MM. Therefore, AMAD-2 is preferable as a positive tissue marker to be incorporated in the optimal immunohistochemical panel for the diagnosis of MM.

Complementary value of five carcinoma markers for the diagnosis of malignant mesothelioma, adenocarcinoma metastasis, and reactive mesothelium in serous effusions

Cytological slides of serous fluids of 41 malignant mesotheliomas, 88 metastatic adenocarcinomas, and 25 reactive effusions were immunostained with the antibodies anti-CEA, MOC-31, Leu-M1, Ber-EP4, and B72.3. Most mesotheliomas and all reactive fluids failed to stain with these antibodies. The sensitivity of the five markers to detect carcinoma cells differed remarkably. Especially MOC-31, Ber-EP4, and B72.3 stained with a high number of carcinoma cases and the complemetary value of Ber-EP4 and B72.3 to immunostain carcinoma cells was impressive: 94% of the metastatic adenocarcinoma cases reacted with Ber-EP4 or B72.3 in contrast to 1 of 41 malignant mesotheliomas.

Calretinin: a novel immunocytochemical marker for mesothelioma

Immunohistochemistry is a powerful diagnostic adjunct in the differential diagnosis between malignant mesothelioma (especially of the epithelial type) and adenocarcinoma metastatic to the serous membranes. Most of the immunological probes commonly used, however, recognize antigens expressed by the epithelial malignancies and absent from mesothelial cells and mesotheliomas. Probes suitable for the positive identification of mesotheliomas are comparatively scarce and much less commonly used because of their reduced sensitivity and specificity, their unsuitability for staining routinely fixed and embedded tissues, or their lack of commercial availability. We now document that two different polyclonal antisera to calretinin consistently immunostain mesothelial cells and malignant mesotheliomas both in routinely fixed and embedded tissue sections and in cytological preparations of serous effusions. The diagnostic sensitivity of this novel immunocytochemical approach reached 100%, allowing immunostaining of all 44 mesotheliomas investigated, which included five biphasic and three sarcomatoid types. The specificity of calretinin immunoreactivity was checked against 294 adenocarcinomas of different origin (19 serosal metastases and 275 primary tumors potentially able to metastatize to serosal membranes) relevant for the discussion of the differential diagnosis with malignant mesothelioma: only 28 cases showed focal immunoreactivity for calretinin. We conclude that calretinin is a most useful marker for the positive identification of malignant mesotheliomas.

Mesothelioma-binding antibodies: thrombomodulin, OV 632 and HBME-1 and their use in the diagnosis of malignant mesothelioma

The aim of this study was to examine the expression of three putative mesothelioma-binding antibodies, thrombomodulin, OV 632 and HBME-1 in 42 malignant mesotheliomas (27 pleural and 15 peritoneal) and 32 pulmonary adenocarcinomas. Evaluation of their use in differentiating between the mesotheliomas and pulmonary adenocarcinomas was assessed. Thrombomodulin was expressed by 22 of 42 (52%) mesotheliomas but was seen in eight of 12 pure epithelial-type mesotheliomas of the pleura and in all four papillary epithelial peritoneal mesotheliomas. For pure epithelial mesotheliomas thrombomodulin was 75% sensitive. Only two of 32 pulmonary adenocarcinomas were immunoreactive yielding a 94% specificity for thrombomodulin. In comparison, OV 632 and HBME-1 showed 67% and 62% antibody sensitivity, respectively, for malignant mesothelioma but this was accompanied by low specificity (OV 632, 37%; HBME-1, 28%). Both OV 632 and HBME-1 are considered unsuitable for use in differentiating between mesotheliomas and pulmonary adenocarcinomas. We advocate the use of thrombomodulin as a mesothelioma-binding antibody in the standard panel of antibodies used in the evaluation of malignant mesothelioma.

Human malignant mesothelial cells: variability of ultrastructural features in established and nude mice transplanted cell lines

The aim of this study was to determine, by transmission electron microscopy, the differentiation features of 21 human malignant mesothelioma cell lines (HMCLs) established from 13 specimens of 12 confirmed human malignant mesotheliomas, and of tumours induced in nude mice injected with 16 HMCLs. Fifty per cent of HMCLs showed typical mesothelial differentiation (long and slender microvilli, desmosomes, perinuclear intermediate filaments); 29 per cent did not show differentiation; and the remainder were poorly differentiated. Three human tumour specimens gave several different HMCLs; the cell lines obtained from a given tumour exhibited variable mesothelial differentiation. Eleven HMCLs were compared with the native tumour. Four were similar to the tumour and seven were less well differentiated, in most cases in relation to their microvilli. With six HMCLs, tumours induced in nude mice were less well differentiated than the corresponding cell lines, whereas with four HMCLs, tumours were equally or better differentiated. However, in most nude mice tumours, typical mesothelial microvilli were present. These results show that cell lines established from malignant mesothelioma may exhibit dedifferentiated features. However, while the variability in ultrastructural differentiation may result from the culture microenvironment, it could also be related to the state of differentiation, of the native tumour sample and to tumour cell heterogeneity.

Keratins 7 and 20 as diagnostic markers of carcinomas metastatic to the ovary

The most common carcinomas metastatic to the ovary that mimic ovarian primaries are colonic adenocarcinomas and endometrial carcinomas. Conventional histochemical staining procedures, even in combination with additional immunohistochemical assays, are of limited value in distinguishing between these metastases and primary ovarian carcinomas. In this study we investigated whether the application of monoclonal antibodies against keratins 7, 8, and 20 could help in differentiating between these categories. The reactivity patterns of 40 carcinomas metastatic to the ovary were compared with those of their primary carcinomas on the one hand and with various primary ovarian carcinomas and mesotheliomas on the other. Colon cancer metastatic to the ovary was keratin 7 negative and keratin 20 positive in 94% of the cases; in contrast, all primary ovarian carcinomas were keratin 7 positive and keratin 20 negative, with the exception of two cases of mucinous cystadenocarcinoma. Ovarian metastases of gastric cancer usually contained keratins 7 and 20. Metastases of endometrial cancer to the ovary and primary ovarian carcinomas usually showed similar keratin expression. We propose that keratin 7 and 20 antibodies may be of help to distinguish between primary ovarian carcinomas and carcinoma metastases in the ovary.

OV 632 and MOC 31 in the diagnosis of mesothelioma and adenocarcinoma: an assessment of their use in formalin fixed and paraffin wax embedded material

AIMS

To investigate the reaction of antibodies OV 632 and MOC 31 in paraffin wax sections as opposed to frozen sections and cytological preparations; to evaluate their usefulness in the differential diagnosis of malignant mesothelioma and secondary adenocarcinoma of the pleura; and to assess the efficacy of microwave pretreatment of sections in unmasking their associated epitopes.

METHODS

Immunohistochemistry, using a standard avidin-biotin technique, with microwave pretreatment and trypsinisation in a certain proportion of cases. The material comprised 43 mesotheliomas, 44 adenocarcinomas and five reactive pleuras.

RESULTS

Epithelial mesotheliomas and the hyperplastic mesothelial cells reacted strongly with OV 632, the reaction with sarcomatoid and desmoplastic tumours was weak, and the reaction with adenocarcinomas was variable. An unequivocal but sometimes patchy positive reaction was obtained with MOC 31 in all but one of the adenocarcinomas; all but one of the mesotheliomas and all the reactive pleuras were negative. Review of the two apparently anomalous cases revealed that the original diagnoses had probably been incorrect. Reactions to both antibodies were abolished by microwave pretreatment, and also by prior trypsinisation in the case of OV 632.

CONCLUSIONS

OV 632 is unsuitable for routine clinical use in paraffin wax embedded material. MOC 31, however, would be a useful addition to a panel of antibodies in the differential diagnosis of mesothelioma and adenocarcinoma in large biopsy and resection specimens and necropsy material. Its value in small biopsy specimens remains to be assessed. Microwave pretreatment does not enhance the reactions with either antibody.

Parathyroid hormone-related protein antigen localization distinguishes between mesothelioma and adenocarcinoma of the lung

The distinction between pleural malignant mesothelioma and pulmonary adenocarcinoma remains a problem in diagnostic histopathology. Parathyroid hormone-related protein (PTHrP) has been demonstrated in the neoplastic cells of malignant mesotheliomata, using a polyclonal antiserum raised to synthetic PTHrP(1-16). In a series of 44 malignant mesotheliomata and 44 cases of pleural adenocarcinomata, PTHrP was localized immunohistochemically in 84 per cent of the mesotheliomata and in 11 per cent of the pleural adenocarcinomata. Normal and reactive mesothelium did not contain detectable PTHrP. The presence of PTHrP in a very high percentage of malignant mesotheliomata indicates the value of including it in the panel of antibodies utilized in the differential diagnosis of mesothelioma.

Limited loss of nine tumor-associated surface antigenic determinants after tryptic cell dissociation

Disodium ethylenediaminetetraacetic acid (EDTA) or trypsin/EDTA are frequently used for the dispersion of monolayer cells into single cell suspensions allowing flow cytometric analysis of surface antigenic determinants. A disadvantage of EDTA is the slow action of this agent, whereas trypsin might affect the antigenic determinants under focus. We studied the possible deleterious effect of trypsin on three different ovarian carcinoma cell lines, COV413b, COV362.c14, and NIH:OVCAR-3, on cell surface antigenic determinants by flow cytometry. Either EDTA or trypsin/EDTA was used for detachment and dissociation of monolayer ovarian cancer cell lines, followed by indirect immunofluorescence with a panel of monoclonal antibodies directed against nine different surface antigenic determinants, including six markers directed against widely distributed antigens. Compared to EDTA, trypsin/EDTA resulted in higher total cell yields and rapid detachment and dissociation into single cell suspensions with significantly lower amounts of dead cells detected by both trypan blue and propidium iodide (PI). Large differences in antigen expression were observed for the different cell lines. However, all antigenic determinants tested could still be detected after tryptic proteolysis. Three antigenic determinants were significantly decreased after trypsin/EDTA compared to EDTA detachment. CA 125 was decreased on COV362.c14 and NIH: OVCAR-3 cells, respectively. BMA 180 and ICAM-1 were decreased on COV413b cells. This cell line-dependent decrease might be caused by differences in glycosylation. We conclude that trypsin/EDTA can be used for rapid monolayer cell detachment with high cell yields and limited loss of antigenic determinants tested.

Immunocytochemical staining of serous effusions: an additional method in the routine cytology practice?

In a consecutive and prospective cytomorphologic and immunocytochemical study we have examined 100 serous fluids with a panel of antibodies. Three different immunocytochemical patterns of staining were recognized: (i) a benign profile showing no Ber-EP4 or CEA-positive cells; (ii) a malignant profile with Ber-EP4 and strongly EMA-positive epithelial cells; and (iii) a malignant profile in which mesothelial cells were strongly positive for EMA. By applying these profiles the number of malignant cases recognized increased from 19 to 38. All cytomorphologic malignant fluids showed a malignant profile, but in two cases a malignant epithelial profile was found in patients without otherwise proven malignant disease (false positive staining). Immunocytochemistry with anti-Ber-EP4 and anti-EMA can be recommended as a routine procedure, but the marker result should always be correlated with cytomorphology, eventual histologic data and clinical records.

Immunocytochemical characterization of cell lines from human malignant mesothelioma: characterization of human mesothelioma cell lines by immunocytochemistry with a panel of monoclonal antibodies

A panel of nine monoclonal antibodies was used to characterize human mesothelioma cell lines that we established from human malignant mesothelioma. The antigens detected were cytokeratin, vimentin, epithelial membrane antigen, carcinoembryonic antigen, Leu-M1 (CD15), desmin, factor VIII-related antigen (von Willebrand factor antigen), OV632, and ME1, a specific monoclonal antibody directed against human malignant mesothelioma. The technique used was the alkaline phosphatase anti-alkaline phosphatase method. All 30 cell lines, either epithelial, sarcomatous, or mixed, showed strong reactivity with cytokeratin and vimentin antibodies. None of the cell lines demonstrated any reactivity with carcinoembryonic antigen, Leu-M1, or factor VIII antibodies; moreover, all of 22 cell lines studied were positive for ME1 antibody and 10 of 12 cell lines studied were positive for OV632. Some interesting features were noted: only two of the 30 cell lines presented a weak positive staining with epithelial membrane antigen, and nine of 19 cell lines tested demonstrated a cytoplasmic staining pattern with desmin antibody. These results show that established human mesothelioma cell lines still possess the immunocytochemical characteristics that are basically consistent with the immunohistochemical features described in tumor tissues of malignant mesothelioma. These characteristics can be used to identify the mesothelioma cells grown from human malignant mesothelioma. Hence, the mesothelioma cell lines will provide a useful tool for the investigation of the cell biology of the tumor and the mechanisms of mesothelial cell transformation, as well as the in vitro evaluation of the effects of some drugs in order to develop new therapies for malignant mesothelioma.

Simultaneous measurement of two cellular antigens and DNA using fluorescein-isothiocyanate, R-phycoerythrin, and propidium iodide on a standard FACScan

Multiparameter flow cytometry is a powerful tool for analyzing the phenotypic, cell kinetic, and ploidy heterogeneity of tumor cell populations. Because of the substantial spectral overlap of propidium iodide (PI) and R-phycoerythrin (PE) fluorescence emission, this combined use of these fluorochromes has been thought not to be feasible on a standard flow cytometer for these kind of studies. Instead of PI, 7-amino-actinomycin D (7-AAD) is used as DNA stain. In this paper however, we show that PI can be used as a DNA stain in combination with fluorescein isothiocyanate (FITC) and R-phycoerythrin (PE) on a standard FACScan. Three established ovarian cancer cell lines (IGROV1, NIH: OVCAR-3, and COV362.c14) were used for these experiments. Cells were fixed with 1.0% paraformaldehyde and permeabilized with various concentrations of lysolecithin for the simultaneous detection of surface antigens by monoclonal antibodies MOv18, BMA180 or OV632, intermediate filament antigens (keratin 18 or vimentin), and DNA. A final concentration of 80 micrograms/ml lysolecithin was found to give optimal results. The emission spectrum overlap from PI into the orange fluorescence channel (FL2) used for PE fluorescence detection could be sufficiently compensated up to a photomultiplier tube potential of about 440 Volts (V) required at the FL2 channel. Using the same instrument settings, 5.10 x 10(4) PE equivalents were detectable. Under these conditions, CVs obtained for the DNA histograms ranged from 3.0-4.1. Application of the method on a mixture of activated peripheral blood lymphocytes and ovarian tumor cells resulted in a clear separation of the two populations both by surface and cytoplasmic antigen expression and DNA content.