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

The Western Australian Mesothelioma Registry: Analysis of 60 years of cases

BACKGROUND AND OBJECTIVE

Australia introduced a partial ban on asbestos consumption in 1984. There is continuing concern about exposure to asbestos in the built environment and non-occupational exposures. The aim of this study was to describe epidemiological trends of mesothelioma in Western Australia (WA) over the 60 years since the first case was recorded.

METHODS

Every case of mesothelioma notified to the WA Cancer Registry is reviewed by an expert panel. Data include demographic and clinical variables including principal mode of asbestos exposure and age at first exposure. Trends over time for survival, latency and pathological subtype of mesothelioma where analysed. Incidence rates for cases exposed during home renovation where calculated.

RESULTS

Two thousand seven hundred ninety-six cases of mesothelioma were identified with males comprising the majority (n = 2368, 84.7%). The median (IQR) age at diagnosis was 70 (62-78) years, and median latency of 47 (38-55) years. Pleural mesothelioma was recorded in 2620 (93.7%) cases with the epithelioid subtype most prevalent (n = 1730, 61.9%). Overall, median survival was 298 (128-585) days and latency 46 (37-54) years, both effectively doubling over the study period. Non-occupational exposures were proportionally higher in females (52.6%), compared with males (9.5%). Home renovation was the primary exposure in 227 (8.1%) cases, with number of cases and incidence rate ratio peaking in 2005/09 but subsequently decreasing.

CONCLUSION

The annual number of cases of mesothelioma in WA may have hit a plateau. The majority of females have non-occupational exposures and incidence rates from home renovation exposure may have peaked, suggesting the ban on asbestos has been effective.

Pleural Mesothelioma: Current Practice and Approach

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diagnosis was aided with the use of special histochemical stains-PAS, D-PAS, and mucicarmine, which now very much have been replaced by immunohistochemical stains.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

Epidemiology and Clinical Aspects of Malignant Pleural Mesothelioma

Mesothelioma is a cancer predominantly of the pleural cavity. There is a clear association of exposure to asbestos with a dose dependent risk of mesothelioma. The incidence of mesothelioma in different countries reflect the historical patterns of commercial asbestos utilisation in the last century and predominant occupational exposures mean that mesothelioma is mostly seen in males. Modern imaging techniques and advances in immunohistochemical staining have contributed to an improved diagnosis of mesothelioma. There have also been recent advances in immune checkpoint inhibition, however, mesothelioma remains very challenging to manage, especially considering its limited response to conventional systemic anticancer therapy and that no cure exists. Palliative interventions and support remain paramount with a median survival of 9-12 months after diagnosis. The epidemiology and diagnosis of mesothelioma has been debated over previous decades, due to a number of factors, such as the long latent period following asbestos exposure and disease occurrence, the different potencies of the various forms of asbestos used commercially, the occurrence of mesothelioma in the peritoneal cavity and its heterogeneous pathological and cytological appearances. This review will describe the contemporary knowledge on the epidemiology of mesothelioma and provide an overview of the best clinical practice including diagnostic approaches and management.

The concept of mesothelioma in situ, with consideration of its potential impact on cytology diagnosis

Diffuse malignant mesothelioma (MM) is an incurable tumour of the serosal membranes, which is often caused by exposure to asbestos and commonly diagnosed at advanced stage. Malignant mesothelioma in situ (MMIS) is now included as diagnostic category by the World Health Organization (WHO). However, our international survey of 34 pulmonary pathologists with an interest in MM diagnosis highlights inconsistency regarding how the diagnosis is being made by experts, despite published guidelines. Whilst the WHO restricts the diagnosis to surgical samples, the very concept has implication for cytological diagnosis, which is already regarded as controversial in itself by some. MMIS is currently only applicable as precursor to MM with an epithelioid component, and raises the possibility for different molecular pathways for different histological MM subtypes. The clinical implications of MMIS at this stage are uncertain, but aggressive therapies are being initiated in some instances. Based on the results of the survey we here present a critical appraisal of the concept, its clinical and conceptual implications and provide practice suggestions for diagnosis. A low threshold for ancillary testing is suggested. The designations of 'malignant mesothelioma, cannot exclude MMIS' or 'atypical mesothelial proliferation with molecular indicators of malignancy, so-called MMIS' could be used on cytology samples, adding 'no evidence of invasion in sample provided' for surgical samples. Clinical and radiological correlation are integral to diagnosis and best done at multidisciplinary meetings. Finally, collaborative studies are required to improve our understanding of MMIS.

Histopathological and immunohistochemical features of 14 peritoneal mesotheliomas with clinical outcomes and recent updates

Background

Malignant peritoneal mesotheliomas (MPMs) are rare tumors with overlapping clinical and histopathological features, especially with epithelial ovarian carcinomas (EOCs). There is no substantial documentation on these rare tumors from our country.

Objective

To study the clinicopathological features including immunohistochemical (IHC) profile and clinical outcomes of 14 MPMs, diagnosed at our institution.

Materials and Methods

This was a retrospective study, wherein 14 cases of MPM, occurring in female patients, diagnosed at our institution, between January 2008 and May 2019 were included, after a critical review.

Results

Median age was 54.5 years. Most patients presented with ascites, omental nodularity, and fat stranding. Microscopically, most cases (11, 78.6%) displayed epithelioid morphology, followed by biphasic pattern (2, 14.3%) and a single case of well-differentiated MPM. IHC, diagnostic sensitivity and specificity of calretinin were 100% (13/13) and 85.7%; of HBME1 were 100% (5/5) and 100%; and of podoplanin (D2-40) were 60% (2/5) and 100%. Other positively expressed immunomarkers were epithelial membrane antigen (n = 2/5, 40%), cytokeratin 5/6 (n = 4/4, 100%), and WT1 (n = 9/10, 90%). Most patients (5/12, 41.7%) were treated with chemotherapy. The 3-year disease-free and overall survival rates were 25.7% and 54%, respectively, including improved survival trend in patients with epithelioid type of MPMs.

Conclusion

MPMs are diagnosed with a combination of clinicopathological features and optimal IHC markers. Their differentiation from EOCs and other metastatic carcinomas is imperative in view of significant treatment implications.

Malignant mesothelioma in situ: diagnostic and clinical considerations

In situ stages of malignancy have been characterised in various neoplasms. Mesothelioma in situ (MIS) has been a controversial diagnosis, lacking clear diagnostic criteria and understanding as to whether it is truly a premalignant lesion in the progression of malignant mesothelioma (MM). Originally understood as a concept and defined as atypical mesothelial proliferation in the presence of invasion, it has now been suggested that loss of nuclear labelling for BRCA1-associated protein-1 (BAP1) in flat, non-invasive mesothelial lesions can define MIS. This study aimed to characterise BAP1 expression in a cohort of 19 patients diagnosed with MIS (either pure MIS, n=3, or MIS-predominant invasive MM, n=16) and to compare survival between MIS, MIS-predominant MM and MM (n=114) in order to gain insight into the characteristics of MIS. We defined pure MIS as any architectural pattern of surface mesothelial cells with loss of BAP1 in the absence of invasion, but in specimens with superficial stromal invasion we also accepted the original definition of cytologically and architecturally atypical mesothelial proliferation, in the absence of inflammatory features, with or without loss of BAP1. We observed that MIS associated with minimal invasion was associated with significantly improved survival compared to MM (8 months vs 22 months). This suggests that MIS is indeed a precursor to MM and that these cases represent earlier stage disease. Loss of BAP1 was present in 60% of mesotheliomas with invasion, so not all early cases can be detected by BAP1 loss, but our study provides evidence that BAP1 loss may be an early molecular alteration in MM pathogenesis in patients that have loss of BAP1. We confirm that BAP1 loss can be useful for diagnosis of pure MIS in surgical specimens, permitting earlier diagnosis. However, identification of a predominant MIS component with minimal invasion has prognostic and conceptual implications. Whilst no approved therapy is available for MIS, close follow up of patients with BAP1 mutation in mesothelial cells and/or diagnosis of MIS is required to monitor for disease progression and potentially investigate earlier treatment interventions.

Malignant pericardial mesothelioma : A systematic review of current practice

BACKGROUND

Malignant mesothelioma is a rare but aggressive tumor, with a high misdiagnosis rate and overall bleak prognosis. In 0.7% of all cases, the origin is the pericardium.

METHODS

The present study is a review of the literature published in recent decades focusing on the advances in clinical manifestations, radiological findings, diagnosis, differential diagnosis, and treatment of malignant pericardial mesothelioma (MPM).

RESULTS

No clear relationship has been established between the etiologies and the development of MPM. Clinical symptoms and signs are nonspecific when present. The main presentations are chest pain and dyspnea. Imaging plays an important role in the detection, characterization, staging, and posttreatment follow-up. The definitive diagnosis is made on the basis of pathological findings. Chest radiography and echocardiography are common techniques used initially, but their roles are limited. Computed tomography and magnetic resonance imaging have an advantage in depicting the thickened pericardium, mediastinal lymph node, tumor, and the extension of adjacent structures. Surgery is the most important treatment modality and remains palliative in most cases, while the roles of chemo- and radiotherapy are unsatisfactory.

CONCLUSION

Clinical trials of malignant pleural and peritoneal mesothelioma remain important for MPM management. Multimodality treatment of surgery, chemotherapy, radiotherapy, and immunotherapy is expected to have a role in the treatment of MPM.

Pleural fluid mesothelin as an adjunct to the diagnosis of pleural malignant mesothelioma

Rationale. The diagnosis of pleural malignant mesothelioma (MM) by effusion cytology may be difficult and is currently controversial. Effusion mesothelin levels are increased in patients with MM but the clinical role of this test is uncertain. Objectives. To determine the clinical value of measuring mesothelin levels in pleural effusion supernatant to aid diagnosis of MM. Methods and Measurements. Pleural effusion samples were collected prospectively from 1331 consecutive patients. Mesothelin levels were determined by commercial ELISA in effusions and their relationship to concurrent pathology reporting and final clinical diagnosis was determined. Results. 2156 pleural effusion samples from 1331 individuals were analysed. The final clinical diagnosis was 183 MM, 436 non-MM malignancy, and 712 nonmalignant effusions. Effusion mesothelin had a sensitivity of 67% for MM at 95% specificity. Mesothelin was elevated in over 47% of MM cases in effusions obtained before definitive diagnosis of MM was established. In the setting of inconclusive effusion cytology, effusion mesothelin had a positive predictive value of 79% for MM and 94% for malignancy. Conclusions. A mesothelin-positive pleural effusion, irrespective of the identification of malignant cells, indicates the likely presence of malignancy and adds weight to the clinical rationale for further investigation to establish a malignant diagnosis.

Diagnostic usefulness of p16/CDKN2A FISH in distinguishing between sarcomatoid mesothelioma and fibrous pleuritis

The distinction between sarcomatoid mesothelioma and fibrous pleuritis is difficult based on histology, especially when the amount of tumor tissue examined via biopsy is small and immunohistochemical examination is inconclusive. We studied the usefulness of deletion of p16 with fluorescence in situ hybridization (FISH) and p16 hypermethylation with polymerase chain reaction for the diagnosis and prognosis of malignant pleural mesothelioma (MPM). We analyzed 50 MPMs, including 22 sarcomatoid mesothelioma cases and 10 fibrous pleuritis cases. We set the cutoff value of homozygous deletion pattern as 14.4% based on FISH signaling patterns using samples of fibrous pleuritis. The percentage of homozygous deletion pattern was higher than 14.4% in 55.6% of the epithelioid mesotheliomas (10/18) and in all of the sarcomatoid mesotheliomas (22/22). Methylation of p16 was observed in 7 (20.6%) of 34 informative cases. p16 FISH analysis can be a reliable test for distinguishing between sarcomatoid mesothelioma and fibrous pleuritis and a prognostic factor for MPM.

Epithelioid Lesions of the Serosa

Context.—Diagnosing epithelioid serosal lesions remains a challenge because numerous different processes—primary or secondary, benign or malignant—occur in body cavities, some of which are very rare.

Objectives.—To review the newest literature and to describe the morphologic criteria and immunohistochemical markers that are useful for distinguishing epithelioid serosal lesions.

Data Sources.—Previously published literature concentrating on the newest research findings. Earlier reviews are principally referred to for established diagnostic criteria.

Conclusions.—Immunohistochemistry with a panel of antibodies has made the diagnosis of epithelioid serosal lesions very reliable. When deciding on antibodies used in differential diagnosis, it is important to consider tumor location, clinical and radiologic information, and morphologic features. Immunohistochemistry is less useful in the differential diagnosis of benign versus malignant mesothelial lesions. The diagnosis of benign versus malignant mesothelial proliferations still relies on the histologic criteria of invasion.

Pathological and molecular biological approaches to early mesothelioma

Malignant mesothelioma is an asbestos-related malignancy that arises primarily from mesothelial cells on the serosal surfaces of the pleural, peritoneal, and pericardial cavities. Malignant pleural mesothelioma (MPM) is most common, and its incidence is dramatically increasing worldwide as a result of widespread use of asbestos. Morphological discrimination between MPM and reactive mesothelial hyperplasia is difficult, and the most reliable pathological criterion for malignancy is mesothelial proliferation invading deeply into subpleural adipose tissues. To establish radical cure of MPM, it is crucial to find early-stage MPM of epithelial type, in which mesothelial proliferation is localized on the serosal surface of parietal pleura or limited within the submesothelial fibrous tissues of parietal pleura. The initial clinical presentation for patients with MPM is frequently dyspnea and/or chest pain due to large pleural effusion, and cytological analysis of pleural effusions is valuable to find patients with early-stage MPM of epithelial type. Recently, cytological features of MPM in pleural effusion, molecular markers for MPM, and genetic alternations of MPM have been reported. In this review, we discuss major issues on pathological and molecular biological approaches for diagnosis of early-stage MPM of epithelial type.

Comparison of immunocytochemical sensitivity between formalin-fixed and alcohol-fixed specimens reveals the diagnostic value of alcohol-fixed cytocentrifuged preparations in malignant effusion cytology

The most commonly used fixative in effusion cytology is formalin. In the present study, the immunocytochemical properties of formalin-fixed and alcohol-fixed specimens were compared to evaluate the usefulness of alcohol-fixed cytocentrifuged preparations for routine cytologic diagnosis. A total of 269 effusion samples and 17 primary antibodies were used. The sensitivity of immunocytochemical studies in alcohol-fixed specimens was similar and correlated to that of formalin-fixed specimens, suggesting that alcohol-fixed cytocentrifuged preparations are useful in effusion cytology. Pretreatment with or without heat-induced antigen retrieval revealed that antigen retrieval was unnecessary for immunocytochemical studies with most primary antibodies in alcohol-fixed cytocentrifuged preparations. The present study describes the use of immunocytochemical studies with alcohol-fixed cytocentrifuged preparations for diagnosis in routine effusion cytology.

Early stages of mesothelioma, screening and biomarkers

The early diagnosis of mesothelioma is notoriously difficult, both from a clinical and pathological perspective. Patients often undergo several medical investigations without definitive diagnosis. The discovery of biomarkers that can be assessed in pleural effusions, histological samples, and serum may assist with the difficult early diagnosis of mesothelioma. In this chapter we focus on those markers that have been examined in the setting of either early diagnosis of mesothelioma in symptomatic individuals or that have been proposed as suitable for screening of asbestos-exposed individuals, with an emphasis on cytology and histology.

Histologic grading and nucleolar organizer regions in oral squamous cell carcinomas

Objective

The purposes of this study were to histologically assess different types of oral squamous cell carcinoma and the silver-binding nucleolar organizer region (AgNOR) morphology in neoplastic cells, as well as to quantify the number of AgNORs in each type of carcinoma in order to relate AgNOR count and histologic grading.

Material and Methods

Twenty-eight cases of oral squamous cell carcinoma were divided into 4 groups, namely well-differentiated, moderately differentiated, poorly differentiated, and undifferentiated. For NOR study, 3-µm-thick sections were stained with 50% aqueous silver nitrate solution. The predominant microscopic pattern of NORs was determined. Quantitative analyses of NORs were obtained of all cells present on each histological field using a 0.025 mm² eyepiece graticule. Different histological fields were analyzed until the total number of NORs was 120 cells for each tumor. Kruskall-Wallis test was applied to compare the groups of sample data at a significance level of p=0.05.

Results

The mean number of AgNORs per nucleus was 3.20 for the well-differentiated group, 5.33 for the moderately differentiated one, 8.27 for the poorly differentiated one, and 10.08 for the undifferentiated one. AgNOR count was significantly different (p<0.05) among all of the studied groups.

Conclusion

AgNOR staining technique seems to be a useful diagnostic tool since differences in AgNOR numeric values can be identified in the different types of oral squamous cell carcinoma. This technique is easy to handle and inexpensive, thus justifying its large use in histopathology.

FISH assay development for the detection of p16/CDKN2A deletion in malignant pleural mesothelioma

Aims

To develop a fluorescence in-situ hybridisation (FISH) assay for detecting p16/CDKN2A deletion on paraffin tissue sections for use as an ancillary test to distinguish reactive from malignant mesothelial proliferations.

Method

Dual-colour FISH for p16/CDKN2A and chromosome 9 (CEP-9) was performed on 11 benign mesothelial proliferations and 54 malignant pleural mesothelioma (MPM) cases to establish cut-off values for p16/CDKN2A deletion. A third MYC probe was used to verify cases showing homozygous deletion. Eight equivocal biopsies were used for assay testing.

Results

Cut-off values for p16/CDKN2A deletion were calculated based on FISH signalling patterns obtained from the benign controls (mean percent nuclei plus three standard deviations). Hemizygous deletion was defined as >44% of nuclei showing the hemizygous (one p16/CDKN2A, two CEP-9 signals) or >15% of nuclei showing the monosomy (one p16/CDKN2A, one CEP-9 signal) deletion patterns. None of the benign cases showed a homozygous deletion pattern (no p16/CDKN2A, at least one CEP-9 signal). In the malignant cases, the percentage of nuclei showing homozygous deletion ranged from 1% to 87%. Therefore, the cut-off value for homozygous deletion was defined as >10%. P16/CDKN2A deletion was detected in 61% (33/54) of MPM cases. Among the equivocal biopsies, four showed homozygous and one showed hemizygous p16/CDKN2A deletion. Age over 60 years, asbestos exposure and p16/CDKN2A deletion were associated with a worse prognosis.

Conclusion

Distinction between benign and malignant mesothelial proliferations can be diagnostically challenging. FISH for p16/CDKN2A deletion is a useful test for confirming the diagnosis of MPM.

Immunocytochemistry of CD146 is useful to discriminate between malignant pleural mesothelioma and reactive mesothelium

Malignant pleural mesothelioma is a refractory tumor with poor prognosis associated with asbestos exposure. Pleural effusion is frequently observed in patients with malignant pleural mesothelioma, and cytological analysis is effective to detect malignant pleural mesothelioma. However, cytological discrimination between malignant pleural mesothelioma and reactive mesothelium is often difficult. Increased expression of CD146, a cell adhesion molecule, has been reported to be closely associated with an advanced stage of malignant melanoma, prostate cancer, and ovarian cancer. In this study, to evaluate the diagnostic utility of CD146 for discrimination between malignant pleural mesothelioma and reactive mesothelium, we examined immunocytochemical expression of CD146 in malignant pleural mesothelioma and reactive mesothelium using two clones of CD146 antibody, OJ79 and EPR3208, on smear specimens of effusion fluids. Immunocytochemical stains were semiquantitatively scored on the basis of immunostaining intensity (0, negative; 1, weak positive; 2, moderate positive; and 3, strong positive). CD146 expression was detected in 15 of 16 malignant pleural mesothelioma with median immunostaining score of 3 by OJ79, and in 19 of 21 malignant pleural mesothelioma with median immunostaining score of 2 by EPR3208. Strong immunoreactivity of CD146 was observed at the apposing surfaces of cell-cell interactions on the plasma membrane of mesothelioma cells. In addition, one OJ79-negative case of malignant pleural mesothelioma was positive for CD146 by EPR3208 and two EPR3208-negative cases of malignant pleural mesothelioma were CD146 positive by OJ79, showing that all 23 malignant pleural mesothelioma cases were positive for CD146 by either OJ79 or EPR3208. On the other hand, CD146 expression was undetectable in all reactive mesothelium cases by OJ79 and EPR3208. The sensitivity of OJ79 and EPR3208 was 94 and 90%, respectively, and the specificity was 100% for both clones. We propose that CD146 is a sensitive and specific immunocytochemical marker enabling differential diagnosis of malignant pleural mesothelioma from reactive mesothelium.

Usefulness of EMA, GLUT-1, and XIAP for the cytologic diagnosis of malignant mesothelioma in body cavity fluids

We compared the effectiveness of epithelial membrane antigen (EMA) with 2 newly described markers, X-linked inhibitor of apoptosis protein (XIAP) and an isoform of glucose transporter (GLUT-1), in the distinction between malignant mesothelioma (MM) and benign effusion (BE) in body cavity fluids. Immunohistochemical studies were performed on cell block sections from 35 cases of histologically confirmed MM and 38 BEs, using antibodies to EMA, XIAP, GLUT-1 (GLUT-1m, monoclonal; GLUT-1p, polyclonal). Results were graded based on the percentage of cells staining: negative (0%), 1+ (<25%), 2+ (25%-49%), 3+ (50%-74%), and 4+ (75%-100%). The performance of each marker was compared using receiver operating characteristic curve analysis. EMA demonstrated the best accuracy, with an area under the curve of 0.91 as compared with XIAP (0.67), GLUT-1m (0.74), and GLUT-1p (0.80). Based on these findings, EMA is a better marker than XIAP or GLUT-1 for the diagnosis of MM.

Metastatic appendiceal mucinous adenocarcinoma to well-differentiated diffuse mesothelioma of the peritoneal cavity: a mimicker of florid mesothelial hyperplasia in association with neoplasms

Atypical/florid mesothelial hyperplasia associated with another neoplastic process is not an infrequent phenomenon and has been reported in a variety of tumors. In those instances, the mesothelial proliferation might create a misdiagnosis of metastatic carcinoma but seldom raises the possibility of a well-differentiated mesothelioma seeded by metastatic neoplastic cells. Herein, we report the case of a 40-year-old woman originally diagnosed with exuberant atypical mesothelial hyperplasia after an diagnostic laparoscopy. The subsequent operation, however, demonstrated a mucinous neoplasm of the appendix with involvement of the peritoneal cavity in the form of peritoneal mucinous carcinomatosis as well as metastases to the uterine serosa and adnexal surfaces. Microscopic analysis revealed an appendiceal adenocarcinoma with signet-ring-cell features that has metastasized to a diffuse well-differentiated mesothelioma of the peritoneal cavity. In many areas, the atypical mesothelial proliferation is indistinguishable from florid mesothelial hyperplasia. The true nature of the mesothelial proliferation was only confirmed after extensive additional sampling, which showed unequivocal stromal invasion. To the best of our knowledge, this is the first report of a metastatic appendiceal mucinous adenocarcinoma to a well-differentiated diffuse mesothelioma of the peritoneal cavity. Although commonly associated with atypical/ florid mesothelial hyperplasia, a carcinoma can rarely metastasize to a well-differentiated mesothelioma, which can pose significant diagnostic difficulties because it can mimic a reactive process. This unusual case report expands the spectrum of mesothelial proliferation in conjunction with a malignant neoplasm and serves to remind pathologists that such a concomitant occurrence exists.

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.

Overexpression and altered glycosylation of MUC1 in malignant mesothelioma

Current interest in the MUC1/EMA mucin relates to its role in malignancy, and its potential as a therapeutic target. MUC1/EMA expression has been observed in the majority of epithelioid mesotheliomas. However, little is known of the characteristics of MUC1/EMA in mesothelioma. Herein, we studied the cell surface and soluble expression of the MUC1/EMA glycoprotein, and determined the mRNA and genomic expression profiles in mesothelioma. We found that the anti-MUC1 antibody, E29, was the most diagnostically useful of seven antibody clones examined with a sensitivity of 84% (16 out of 19 cases) and no false positive results. MUC1 mRNA expression was significantly higher in mesothelioma samples than in benign mesothelial cells. No amplification of the MUC1 gene was observed by FISH. Seven of 9 mesothelioma samples expressed MUC1-secreted mRNA isoform in addition to the archetypal MUC1/transmembrane form. CA15.3 (soluble MUC1) levels were significantly higher in the serum of mesothelioma patients than in healthy controls but were not significantly different to levels in patients with benign asbestos-related disease. CA15-3 in effusions could differentiate malignant from benign effusions but were not specific for mesothelioma. Thus, as in other cancers, alterations in MUC1 biology occur in mesothelioma and these results suggest that specific MUC1 characteristics may be useful for mesothelioma diagnosis and should also be investigated as a potential therapeutic target.

The diagnostic value of Ki-67 and repp86 in distinguishing between benign and malignant mesothelial proliferations

CONTEXT

The differentiation of benign mesothelial proliferations from malignant mesotheliomas may be difficult, especially when evaluating small specimens from pleural biopsies.

OBJECTIVE

To explore the potential value of 2 proliferative cell markers, Ki-67 and restrictedly expressed proliferation-associated protein 86 kDa (repp86), in distinguishing between malignant mesothelioma (MM) and benign reactive mesothelial hyperplasia (MH).

DESIGN

Thirty-six cases of MM from 26 men and 10 women with a mean age of 62.9 years (range, 36-80 years) and 22 cases of benign reactive MH from 14 male and 8 female patients with a mean age of 51.5 years (range, 15- 88 years) were included in this study. The proliferative status of the lesions was assessed by immunohistochemistry using monoclonal antibodies to Ki-S2 (repp86) and Ki-S5 (Ki-67). The labeling indices were quantified.

RESULTS

The mean labeling indexes for Ki-67 in MM and benign reactive MH were 24.6% (range, 1%-66%) and 6.23% (range, 0%-25%), respectively. The mean labeling indexes for repp86 in MM and benign reactive MH were 26.3% (range, 0%-50%) and 3.26% (range, 0%- 21%), respectively. The average proliferative cell count was significantly higher in MM compared with benign reactive MH (P < .001). Furthermore, both markers showed a significant correlation in their expression in MM and benign reactive MH (r = 77.5, P < .001). Sensitivities of 88% and 92% and specificities of 92% and 94% were obtained at a cutoff point of 9% for Ki-67 and repp86, respectively.

CONCLUSIONS

Used in combination, Ki-67 and repp86 appear to be useful markers in differentiating MM from benign reactive MH.

Accuracy and reproducibility of pleural effusion cytology

The increasing number of Malignant Mesothelioma (MM) cases that arrive for expert examinations to court for compensation reasons in subjects exposed to asbestos, in many instances rely exclusively on cytological smears of pleural effusion. We evaluated the accuracy and reproducibility of cytological pleural effusions, based on morphological criteria alone. Nine pathologists and eight residents from seven institutions in north-east Italy blindly examined 45 smears of MM (17), metastases (14) and benign effusions (14), in two rounds. Diagnoses had been confirmed by immunohistochemical and clinical follow-up, and eventually at autopsy. Diagnostic accuracy, interobserver and intraobserver agreement in the distinction of benign vs malignant cases, and in the differentiation of primary from metastatic malignancies, were evaluated. The distinction of benign from malignant smears resulted rather satisfactory (k=0.514), but markedly decreased in differentiation of MM from metastases (overall agreement: k=0.343), as well as when readings from residents were analyzed (k=0.132). Cytology is a useful and reliable tool in the identification of malignancies, but when the distinction of primary from metastatic tumors is addressed morphological criteria alone are not sufficient for a definite diagnosis of MM and the use of cell blocks, immunohistochemistry (IHC) and molecular ancillary techniques are recommended.

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.

My approach to the diagnosis of mesothelial lesions

Mesothelial lesions pose considerable diagnostic challenges not only because benign tumours, reactive proliferations and malignant mesothelioma can mimic one another, but also because the morphological patterns displayed by malignant mesothelioma can simulate a variety of epithelial and non-epithelial malignancies. Immunohistochemical markers can aid in distinguishing epithelioid malignant mesothelioma from metastatic adenocarcinoma, but because no single marker reliably separates all cases, a panel of stains is recommended. Immunohistochemical studies are of more limited value in sarcomatoid malignant mesothelioma, and other features often play an essential role. The separation of reactive mesothelial proliferations from malignant mesothelioma on small biopsy can be quite difficult, as distinguishing features, such as stromal invasion, often cannot be adequately assessed. In adequately sampled lesions, however, the distinction between malignant mesothelioma, benign mesothelial proliferations and other tumours can be achieved in most cases by using a carefully integrated approach that incorporates clinical and radiographic data, immunohistochemical studies and, in selected cases, histochemical and ultrastructural techniques.

The diagnosis of malignancy in effusion cytology: a pattern recognition approach

This review presents a pattern recognition approach for the diagnosis of malignant effusions. The cytomorphologic features of reactive mesothelial proliferation, mesothelioma and metastatic carcinoma are presented. In addition, the role of ancillary studies in challenging cases and the importance of integrating clinical findings are stressed. An algorithmic approach to the workup of serous effusions as well as pitfalls for false-positive diagnosis are discussed.

The immunohistochemical profile of malignant mesotheliomas of the tunica vaginalis: a study of 20 cases

Malignant mesotheliomas of the testis arise from the tunica vaginalis, formed from the evagination of the abdominal peritoneum into the scrotum. The immunohistochemical profile of the tunica vaginalis and associated neoplasms is often extrapolated from thoracic studies. Testicular series are uncommon, usually derived from previous case studies and literature reviews. The immunohistochemical findings in 20 cases originally diagnosed as malignant mesotheliomas are presented. Archival testicular malignant mesothelioma specimens from 1959 to 2004 were collected from hospitals throughout the United Kingdom and from the authors' own archives. Hematoxylin and eosin-stained sections were reviewed, and selected sections from each case were then examined using an immunohistochemical panel of eight antibodies: calretinin (Zymed, 1:200), epithelial membrane antigen (EMA) (DAKO, 1:50), thrombomodulin (DAKO 1:5), CK7 (DAKO, 1:100), CK5-CK6 (DAKO, 1:10), BerEp4 (DAKO, 1:25), carcinoembryonic antigen (CEA) (DAKO, 1:10), and CK20 (DAKO, 1:100). The EnVision technique was used for all antibodies. Sections were reviewed independently by three pathologists. Electron microscopy was performed on selected cases. In all cases, the morphologic light microscopy criteria for a diagnosis of malignant mesothelioma were present. However, two tumors were later excluded from the study because of diffuse strong positive immunostaining with CK20 and BerEp4 and an ultrastructural appearance of adenocarcinoma. Of the remaining cases, 15 of 18 (83%) were purely epithelioid in type, showing a mixture of papillary, tubular, and solid patterns, and 3 of 18 (17%) showed a mixed sarcomatoid/epithelioid pattern. All cases were positive for calretinin and EMA (100%), 16 of 18 (89%) were positive for thrombomodulin, and 15 of 18 (83%) were positive for CK7. CK5-CK6 positivity was present in 13 of 18 (72%) but varied in strength and distribution; 2 of 18 (11%) were positive for BerEp4. All the cases were negative for CK20 and CEA. Four of the 18 cases were examined by electron microscopy, which revealed long thin microvilli supporting a diagnosis of malignant mesothelioma. This study has shown that the immunocytochemical profile of testicular malignant mesotheliomas is similar to those arising in the pleura, with diffuse positivity for calretinin, EMA, thrombomodulin, and CK7, and negative for CK20 and CEA. Focal weak positivity may be encountered with BerEp4. However, histopathologists should be aware of the variability in CK5-6 staining in testicular specimens when compared with pleural mesotheliomas.

Cell proliferation rate and telomerase activity in the differential diagnosis between benign and malignant mesothelial proliferations

AIMS

The differential diagnosis of malignant mesothelioma (MM) from benign mesothelial lesions (BML) based on histopathological criteria is sometimes not satisfying and causes diagnostic problems for histopathologists. We aimed to investigate whether the immunohistochemically determined cell proliferation rate and telomerase activity, using Ki-67 and human telomerase reverse transcriptase (hTERT) immunohistochemistry, respectively, are useful in the differential diagnosis of MM from BML.

METHODS

Sixty-six cases of MM (33 epithelioid, 30 biphasic and 3 sarcomatoid) and 22 cases of BML (15 reactive mesothelial proliferations and 7 fibrous pleuritis/pericarditis) were included in this study. We evaluated the proliferative activity by Ki-67 and telomerase activity by hTERT immunohistochemistries for each case.

RESULTS

The mean value of the Ki-67 proliferation index (PI) in MMs was significantly higher than that of BMLs. Biphasic MMs have higher a Ki-67 PI than epithelioid and sarcomatoid types. Ki-67 immunohistochemistry has a sensitivity of 74%, specificity of 86% and positive predictive value of 94% in detecting MM. hTERT immunohistochemistry detected MM with sensitivity and specificity of 68%.

CONCLUSION

As a result, being cheap and simple methods, Ki-67 and hTERT immunohistochemistries can be used in differentiating malignant and benign mesothelial lesions in routine formalin-fixed, paraffin-embedded material.

Differential diagnosis of benign and malignant mesothelial proliferations on pleural biopsies

CONTEXT

Although much of the pathology literature focuses on differential diagnosis of diffuse malignant mesothelioma from other types of cancer, the primary diagnostic challenge facing the pathologist is often whether a mesothelial proliferation on a pleural biopsy represents a malignancy or a benign reactive hyperplasia.

DESIGN

Based on previous medical publications, extensive personal consultations, and experience on the United States-Canadian Mesothelioma Reference Panel and the International Mesothelioma Panel, salient information was determined about interpretation of benign versus malignant mesothelial proliferations on pleural biopsies.

RESULTS

Differentiation of benign reactive mesothelial hyperplasia from diffuse malignant mesothelioma is often difficult. Benign reactive mesothelial hyperplasia may mimic many features ordinarily associated with malignancy, and diffuse malignant mesothelioma may be cytologically bland. Entrapment of benign reactive mesothelial cells within organizing pleuritis may mimic tissue invasion.

CONCLUSIONS

Various histologic clues favor a benign over a malignant mesothelial proliferation and vice versa. Invasion is the most reliable criterion for determining that a mesothelial proliferation is malignant. When there is any doubt that a pleural biopsy represents a malignancy, we recommend a diagnosis of atypical mesothelial proliferation.

Malignant mesothelioma

Malignant mesothelioma is an aggressive, treatment-resistant tumour, which is increasing in frequency throughout the world. Although the main risk factor is asbestos exposure, a virus, simian virus 40 (SV40), could have a role. Mesothelioma has an unusual molecular pathology with loss of tumour suppressor genes being the predominant pattern of lesions, especially the P16INK4A, and P14ARF, and NF2 genes, rather than the more common p53 and Rb tumour suppressor genes. Cytopathology of mesothelioma effusions or fine-needle aspirations are often sufficient to establish a diagnosis, but histopathology is also often required. Patients typically present with breathlessness and chest pain with pleural effusions. Median survival is now 12 months from diagnosis. Palliative chemotherapy is beneficial for mesothelioma patients with high performance status. The role of aggressive surgery remains controversial and growth factor receptor blockade is still unproven. Gene therapy and immunotherapy are used on an experimental basis only. Patterns identified from microarray studies could be useful for diagnosis as well as prognostication.

The value of epithelial membrane antigen expression in separating benign mesothelial proliferation from malignant mesothelioma: A comparative study

Differentiating reactive mesothelial (RM) proliferation from malignant mesothelioma (MM) can be cytologically challenging. There have been discordant studies reporting the value of epithelial membrane antigen (EMA) in differentiating RM from MM. In this study, we investigated the expression of two different clones of EMA in RM and MM. Twenty cases of pleural effusion smears of RM and 20 cases of MM with their corresponding cell blocks were retrieved from the hospital computer system. Diagnosis of MM was confirmed by surgical decortication or pneumonectomy with immunostaining studies and/or electron microscopy. Cases of RM were confirmed by clinical history and histology. Cell blocks were formalin-fixed, paraffin-embedded, and immunostained for EMA clone Mc5 and EMA clone E29. The positive rates for clone Mc5 were 14/20 (70%) for MM and 12/20 (60%) for RM and EMA clone E29 were 15/20 (75%) for MM and 0/20 (0%) for RM. The sensitivity and specificity for EMA clone Mc5 were 70 and 40%, respectively. For EMA clone E29, the sensitivity and specificity were 75 and 100%, respectively. In conclusion, both RM and MM immunostained for EMA clone Mc5, indicating that it is not a reliable immunocytochemical marker for differentiating RM from MM. EMA clone E29 was negative in all cases of RM and positive in 75% of MM and therefore is a reliable immunocytochemical marker for differentiating RM from MM.

Paratesticular mesothelial proliferations

Varied mesothelial proliferations are found around the testes. Benign reactive mesothelial proliferations in hydrocoeles may be very florid and histologically worrisome, but these can usually be separated from malignant mesotheliomas of the tunica vaginalis because they are confined to a sharply demarcated zone near the luminal surface. In addition, benign inflamed hydrocoeles tend to show a distinct zonation with cellular areas near the luminal surface and more fibrotic areas beneath. The proliferating mesothelial cells in benign reactions often form lines that are parallel to the surface of the hydrocoele. Malignant mesotheliomas of the tunica vaginalis are usually grossly visible as single or multiple nodules. Histologically, they show an epithelial- or mixed epithelial- and sarcomatous-morphologic image, with evidence of stromal invasion. Well-differentiated papillary mesotheliomas are usually solitary exophytic nodules with a distinctive morphologic appearance and benign course, but they must be carefully separated from malignant mesotheliomas with a focally exophytic papillary growth pattern. By definition, well-differentiated papillary mesotheliomas do not exhibit stromal invasion. Peritesticular adenomatoid tumors are also very common; they are benign circumscribed cellular nodules with an appearance comparable to that of adenomatoid tumors in other body locations such as the uterine serosa.

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.

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

AIMS

The differentiation of benign pleural conditions from malignant mesothelioma may be difficult, especially with a small biopsy. We have tested the hypothesis that assessment of the cell cycle status is of value in the histopathological diagnosis of such biopsies, by comparing 33 malignant mesotheliomas with 36 cases of reactive mesothelial hyperplasia and reactive pleural fibrosis.

METHODS AND RESULTS

Biopsies were investigated for proliferative status by immunostaining for a novel antibody, MCM2, all of which showed nuclear expression of MCM2 at higher frequency than Ki67 (P < 0.0001). Counts in areas of maximum tumour staining showed significantly higher labelling indices (LIMax) in epithelioid and sarcomatoid mesotheliomas compared with reactive mesothelial hyperplasia and reactive pleural fibrosis (P < 0.0001 for both). Average counts (LIAve) revealed a significant increase in epithelioid mesothelioma compared with reactive mesothelial hyperplasia (P < 0.0001).

CONCLUSION

We consider MCM2 to be a useful adjunct in the differential diagnosis of malignant mesothelioma.

Long microvilli of mesothelioma are conspicuous in pleural effusions processed by Ultrafast Papanicolaou stain

BACKGROUND

The differentiation of malignant epithelial mesothelioma, nonmucinous pulmonary adenocarcinoma, and mesothelial hyperplasia by direct light microscopic examination is challenging. The detection of long microvilli, an ultrastructural feature unique for malignant epithelial mesothelioma, requires immunolabeling of epithelial membrane antigen to be visible by light microscopy. The purpose of this study is to report that this feature is now made conspicuous enough to be detected by light microscopy by a different approach in cytologic processing.

METHODS

The study includes 9 cases of mesothelioma, 50 cases of mesothelial hyperplasia, and 50 cases of nonmucinous pulmonary adenocarcinoma. Direct smears were made from the sediments of fresh or refrigerated effusions, air dried, rehydrated with normal saline for 30 seconds to create retraction halos, and processed with the Ultrafast Papanicolaou stain (UFP).

RESULTS

Long microvilli in thick bundles as well as short, fine projections radiating from the free surface of the epithelial mesothelioma cells were observed within the retraction halos in pleural effusions processed by UFP. These features were not observed in the UFP-processed hyperplastic mesothelial cells or in the pulmonary nonmucinous adenocarcinoma cells.

CONCLUSION

Direct visualization of long microvilli via UFP may aid in the distinction of malignant mesothelioma from mesothelial hyperplasia and adenocarcinoma before immunohistochemical and electron microscopic studies are performed.

The use of CDKN2A deletion as a diagnostic marker for malignant mesothelioma in body cavity effusions

BACKGROUND

The distinction between benign reactive mesothelial cells and malignant mesothelial cells in serous effusions is difficult and has an unusually high false negative rate. Unfortunately, there are no generally accepted markers to distinguish between benign reactive and malignant mesothelial cells. Homozygous deletion of CDKN2A is frequent in mesothelioma (present in > 70% of tumors). Therefore, detection of CDKN2A deletion by fluorescence in situ hybridization (FISH) was evaluated as an ancillary test in the cytologic diagnosis of malignant mesothelioma.

METHODS

Dual-color FISH for CDKN2A and chromosome 9 centromere was performed on cytolyt-fixed Thinprep slides from 6 cytologically suspicious and 7 cytologically positive effusions (all with histologically confirmed mesothelioma) and in 19 cytologically benign effusions (14 pleural effusions, 3 pericardial effusions, and 2 abdominal fluid specimens). Specimens containing > or = 15 nuclei that lacked signals for CDKN2A but showed at least 1 signal for chromosome 9 centromere were considered positive. In samples with negative cytology, the nuclei of at least 100 mesothelial cells were evaluated; whereas, in specimens with positive or suspicious cytology, counting nuclei was done only if < 15% of nuclei showed homozygous loss of CDKN2A.

RESULTS

Homozygous deletion was detected in mesothelial cells in six of seven specimens with positive cytology and in six of six specimens with suspicious cytology. Cytologically, there were numerous tumor cells in a single positive specimen without homozygous deletion. All 19 cytologically negative specimens were negative for CDKN2A deletion.

CONCLUSIONS

The detection of homozygous CDKN2A deletion by FISH would have been helpful in confirming a diagnosis of mesothelioma over reactive mesothelial cells in 12 of 13 samples with positive or suspicious cytology. Further studies on larger series of patients with suspicious cytology are needed to evaluate the validity and efficiency of this approach for improving the diagnostic accuracy of effusion cytology.

Immunohistochemical analysis still has a limited role in the diagnosis of malignant mesothelioma. A study of thirteen antibodies

To identify the most accurate and useful panel to diagnose mesothelioma, we immunostained sections from 112 mesotheliomas, 18 adenocarcinomas, and 11 reactive pleural specimens with 13 antibodies. Positive results for mesotheliomas, adenocarcinomas, and reactive pleura, respectively, were CAM5.2, 111, 18, and 11; vimentin, 30, 3, and 3; HBME-1, 75, 10, and 8; thrombomodulin, 31, 2, and 2; calretinin, 43, 6, and 11; and CD44H, 68, 10, and 4. Positive results for adenocarcinoma markers in mesotheliomas and adenocarcinomas, respectively, were carcinoembryonic antigen, 1 and 15; LeuM1, 7 and 9; and Ber-EP4, 5 and 12. All reactive pleura were negative. Positive results for markers to help distinguish mesothelioma from reactive pleura in mesotheliomas, adenocarcinomas, and reactive pleura, respectively, were epithelial membrane antigen, 76, 17, and 6; p53, 78, 16, and 9; P-170 glycoprotein, 37, 4, and 2; and platelet-derived growth factor receptor beta, 31, 1, and 2. The differential diagnosis of mesothelioma from adenocarcinoma is based on negative markers. Individual mesothelial markers are of low sensitivity and specificity for mesothelioma. However, diagnostic accuracy is improved by the use of antibody panels. To date there are no antibodies that help distinguish mesothelioma from reactive pleura.

Malignant pleural mesothelioma

Malignant pleural mesothelioma remains a difficult tumor to treat, much less cure. Currently, the best chance for long-term survival lies with early diagnosis and aggressive surgical extirpation, but given the typically long delay between the onset of symptoms and diagnosis, this is only possible with a high index of suspicion and an aggressive diagnosis workup. Early referral to a tertiary center experienced in the treatment of MPM may be important for several reasons: (1) decreased risk of tumor spread along multiple thoracenesis/biopsy tracts, (2) the availability of specialized pathologic assays for definitive diagnosis, (3) the availability of critical staging modalities (aggressive mediastinoscopy +/- thoracoscopy, MRI scans performed according to specific mesothelioma protocols, and perhaps PET scans), (4) surgical experience with pleurectomy/decortication and/or extrapleural pneumonectomy, that may decrease morbidity and mortality, and (5) the availability of novel adjuvant protocols. Single-modality therapy is unlikely to result in long-term survival. Aggressive surgery is required for optimal debulking, and extrapleural pneumonectomy may offer better local control compared with pleurectomy/ecortication. Delivery of optimal radiation schedules, which may involve large fractions as well as large total doses, is limited by the presence of nearby dose-limiting structures. Current chemotherapy is severely lacking in producing objective responses and improved survival although gemcitabine and IL-2 may be active agents to be combined with radiation and/or other agents. Hyperthermia, photodynamic therapy, intracavitary therapy, and gene therapy are all relatively new techniques under active investigation that should be supported by enrollment in on-going protocols. Predictably, many of these techniques provide greater benefit when used in the setting of adjuvant protocols or minimal residual disease, emphasizing the importance of multimodality therapy.

Pleural fluid cytology: immunocytochemistry usage patterns and significance of nondefinitive diagnoses

There has been little study of how pleural fluids are interpreted in actual practice, including the use of immunocytochemistry and nondefinitive diagnoses. Pleural fluid reports (n = 1,330) from 1991-1997 and the University of Iowa cancer database were retrospectively reviewed to determine the cytologic diagnosis, requisition form history, patient survival, and use of immunocytochemistry. Nondefinitive diagnoses were made in 11.3% of cases. Immunocytochemistry was used in 2.6% of cases and aided in making a definitive diagnosis in 71.9% of cases. For patients with a clinical suspicion of malignancy, the percentages of patients who had a nondefinitive, benign, and malignant diagnosis and died of disease were 81.6%, 94.0%, and 90.6%, respectively. In conclusion, if patients had a history of malignancy and a clinical suspicion of recurrence, patient survival was dismal, regardless of the cytologic diagnosis. Immunocytochemistry was used sparsely but often aided in making a definitive diagnosis.

Immunohistochemical evidence for mesothelial origin of paratesticular adenomatoid tumour

AIMS

To investigate the histogenesis of paratesticular adenomatoid tumour by use of immunohistochemical markers for a variety of carcinomas and mesothelioma.

METHODS AND RESULTS

Immunohistochemical staining of sections from 12 cases of paratesticular adenomatoid tumour was undertaken using primary antibodies to antigens expressed by benign epithelial cells and carcinoma (cytokeratin AE1/AE3, cytokeratin 34ssE12, epithelial membrane antigen, MOC-31, Ber-EP4, CEA, B72.3, LEA.135, Leu M1), stromal and vascular markers (vimentin, CD34, factor VIII), and mesothelioma-associated antigens (thrombomodulin, HBME-1, OC 125) and p53 protein. There was absence of immunohistochemical expression of epithelial/carcinoma markers MOC-31, Ber-EP4, CEA, B72.3, LEA.135, Leu M1 and to factor VIII and CD34. All tumours expressed cytokeratin AE1/AE3, epithelial membrane antigen and vimentin, with weak expression of cytokeratin 34ssE12 in 25% of tumours. Each tumour showed expression of thrombomodulin, HBME-1 and OC 125 in a membranous distribution. p53 protein expression was not detected.

CONCLUSIONS

The immunohistochemical profile of paratesticular adenomatoid tumour is strongly supportive of a mesothelial cell origin.

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.