The comparative accuracy of different pleural biopsy techniques in the diagnosis of malignant mesothelioma.

AIMS: To evaluate the diagnostic accuracy of closed and open pleural biopsies in diagnosing malignant pleural mesothelioma. METHODS AND RESULTS: The autopsy study group comprised 45 malignant mesotheliomas. All prior pleural biopsy investigations were reviewed. Forty-one of 45 (91%) had had an antemortem diagnosis of malignant mesothelioma. In these 41 cases, 57 prior diagnostic pleural biopsies had been performed [36 closed needle biopsies: 31 blind; five computed tomography (CT)-guided and 21 open pleural biopsies]. For definitive diagnosis open pleural biopsy yielded a sensitivity of 95% and specificity of 100%. For definitive diagnosis closed blind pleural biopsies yielded a sensitivity of 16% and specificity of 94%. Thirty-two per cent of 'blind' biopsies were inadequate. CT-guided pleural biopsies yielded a definitive diagnostic accuracy of 100% (5/5). Biopsy specimen size was important in obtaining a positive definitive diagnosis. Diagnosis was attained in 75% of specimens >10 mm in size compared with 8% <10 mm in size. CONCLUSIONS: Overall, all procedures had utility but definitive diagnostic accuracy for 'blind' closed pleural biopsy was low (16%), dependent on biopsy specimen size and tumour subtype. Sarcomatoid subtype malignant mesothelioma yielded the lowest diagnostic accuracy. For all subtypes of malignant mesothelioma, open pleural biopsy produced the highest diagnostic accuracy (100% sensitivity, 95% specificity).

EGFR and PDGFR differentially promote growth in malignant epithelioid mesothelioma of short and long term survivors.

BACKGROUND: Malignant pleural mesothelioma (MPM) is an asbestos related tumour difficult to detect early and treat effectively. Asbestos causes genetic modifications and cell signalling events that favour the resistance of MPM to apoptosis and chemotherapy. Only a small number of patients, approximately 10%, survive more than 3 years. The aim of our study was to assess possible differences within signalling pathways between short term survivors (survival <3 years; STS) and long term survivors (survival >3 years; LTS) of MPM. METHODS: 37 antibodies detecting proteins engaged in cell signalling pathways, enforcing proliferation, antiapoptosis, angiogenesis and other cellular activities were investigated by tissue microarray (TMA) technology. RESULTS: Epidermal growth factor receptor (EGFR) was expressed stronger in LTS whereas platelet derived growth factor receptor (PDGFR) signalling was more abundant in STS. Expression of TIE2/Tek, a receptor for tyrosine kinases involved in angiogenesis, was differentially regulated via PDGFR and thus is more important in STS. Antiapoptosis was upregulated in STS by signal transducer and activator of transcription 1 (STAT1)-survivin and related molecules, but not in LTS. Our study provides novel insights into the regulatory mechanisms of signalling pathways in MPM, which differentially promote tumour growth in LTS and STS. CONCLUSION: We have demonstrated that small scale proteomics can be carried out by powerful linkage of TMA, immunohistochemistry and statistical methods to identify proteins which might be relevant targets for therapeutic intervention.

The pathology associated with therapeutic procedures in malignant mesothelioma.

AIMS: To describe iatrogenic pathological lesions in malignant pleural mesothelioma. METHODS AND RESULTS: All cases of malignant pleural mesothelioma confirmed by antemortem pleural biopsy and undergoing post mortem examination over a 7-year period (1995-2001) formed the study group. This comprised 48 malignant pleural mesotheliomas [epithelioid (n = 21), biphasic (n = 14) and sarcomatoid (n = 13)]. Twenty-eight of 48 (58%) had received chemical (talc) pleurodesis, 30/48 (63%) palliative localized radiotherapy, 6/48 (13%) chemotherapy, and 14/48 (30%) surgery [12/48 (26%) pleural decortication and 2/48 (4%) pleuropneumonectomy]. CONCLUSIONS: Talc pleurodesis induces a marked pseudosarcomatous fibroblastic proliferation which may impart a biphasic pattern to the neoplasm. In more chronic cases, paucicellular fibrosis with a foreign body giant cell reaction is noted. The talc is polarizable and deposited in linear fashion within the tumour. In 2/28 (7%) pleurodesis cases platyform ferruginous bodies were seen in the peripheral alveolated lung parenchyma and these mimicked asbestos bodies. An awareness of this is important to prevent false attribution to asbestos. Talc could be identified by transmission electron microscopic mineral analysis in 5/15 (33%) cases examined. Tumour nodules developing subjacent to iatrogenic wound sites were noted in 8/48 (17%) cases. In 6/8 (75%) of these cases, comparative assessment of the locally irradiated subcutaneous chest wall tumour, with background pleural mesothelioma, showed no morphological difference in architectural tumour growth pattern, extent of necrosis, cytological or nuclear pleomorphism, mitotic activity or tumour immunophenotype. In 2/8 (25%) cases the locally irradiated tumour showed prominent bizarre multinucleated tumour giant cells and intense mixed inflammation, a feature not seen in the background (non-irradiated) tumour. All six malignant pleural mesotheliomas receiving chemotherapy appeared refractory to treatment in that chemotherapy did not appear to have any significant effect on the tumour morphology, cytonuclear pleomorphism, mitotic activity, extent of necrosis or immunophenotype. In the 12 decortication specimens and two pleuropneumonectomy resections, post mortem examination identified evidence of residual malignant mesothelioma of similar morphological subtype and immunophenotype to the resected tumour.

Inter-observer variation between pathologists in diffuse parenchymal lung disease.

BACKGROUND: There have been few inter-observer studies of diffuse parenchymal lung disease (DPLD), but the recent ATS/ERS consensus classification provides a basis for such a study. METHODS: A method for categorising numerically the percentage likelihood of these differential diagnoses was developed, and the diagnostic confidence of pathologists using this classification and the reproducibility of their diagnoses were assessed. RESULTS: The overall kappa coefficient of agreement for the first choice diagnosis was 0.38 (n = 133 biopsies), increasing to 0.43 for patients (n = 83) with multiple biopsies. Weighted kappa coefficients of agreement, quantifying the level of probability of individual diagnoses, were moderate to good (mean 0.58, range 0.40-0.75). However, in 18% of biopsy specimens the diagnosis was given with low confidence. Over 50% of inter-observer variation related to the diagnosis of non-specific interstitial pneumonia and, in particular, its distinction from usual interstitial pneumonia. CONCLUSION: These results show that the ATS/ERS classification can be applied reproducibly by pathologists who evaluate DPLD routinely, and support the practice of taking multiple biopsy specimens.

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

AIMS: To undertake a clinicopathological study of diffuse serosal neoplasms of epithelial histogenesis which clinically and pathologically mimic malignant pleural mesothelioma. METHODS AND RESULTS: Over a 10-year (1990-2000) study period 53 carcinomas mimicking diffuse pleural mesothelioma ('pseudomesotheliomatous' carcinoma) were identified. The study group comprised 50 men and three females, age range 33-77 (median 68) years. In 46 (87%) cases there was a history of smoking and in 40 (76%) cases a history of asbestos exposure. Histologically the pleural 'pseudomesotheliomatous' carcinomas could be divided into two broad groups: primary pulmonary carcinomas with florid pleurotropic growth (n = 47), of which 34 (70%) were adenocarcinomas; and diffuse carcinomatous involvement of the pleura by metastatic tumour (n = 6). This latter group comprised two transitional cell carcinomas of bladder, one renal (clear) cell carcinoma, one ductal pancreatic adenocarcinoma, one prostatic adenocarcinoma and one squamous cell carcinoma of parotid gland origin. Follow-up data were available in 35 cases. Regardless of tumour type, survival was poor (median 8 months) and comparable to diffuse pleural mesothelioma. CONCLUSIONS: Pleural 'pseudomesotheliomatous' carcinomas are uncommon (comprising 6% of referrals), pathologically heterogeneous tumours with poor prognosis. Tissue diagnosis should be obtained in all cases of suspected diffuse pleural neoplasia. By light microscopy and immunophenotype many of the tumours mimicked malignant mesothelioma. In particular, an awareness that all neoplasms exhibiting squamous differentiation may express cytokeratin 5/6 and thrombomodulin is important to prevent misinterpretation. In this respect, calretinin is regarded as the most specific and sensitive mesothelial marker. Misdiagnosis may have medico-legal implications in asbestos-related compensation claims.

Synchronous diffuse malignant mesothelioma and carcinomas in asbestos-exposed individuals.

AIMS: The development of synchronous diffuse malignant mesothelioma and carcinoma in individuals exposed to asbestos is rare. We report nine cases and discuss the medico-legal implications. METHODS AND RESULTS: Five hundred patients seeking compensation for asbestos-related diffuse malignant mesothelioma were reviewed with access to post-mortem data. The study group comprised cases in which a second (non-mesothelial) neoplasm was identified. The study group comprised eight males, one female, mean age 68 years (range 60-75). All individuals gave a history of asbestos exposure. Synchronous malignant mesothelioma with carcinoma was identified in 9/500 (1.8%). Eight malignant mesotheliomas were pleural, one was primary peritoneal in origin. By morphological subtyping there were four epithelioid, three biphasic and two sarcomatoid mesotheliomas. In 6/9 (67%) the second tumour was a primary bronchogenic carcinoma (three adenocarcinomas, two squamous cell carcinomas and one small-cell carcinoma). In 3/9 (33%) the second tumour was a non-bronchogenic carcinoma (colonic, pancreatic and breast ductal adenocarcinoma). No other neoplasms were identified in the cohort of malignant mesotheliomas studied. Five persons had pathological evidence of asbestosis (four had bronchogenic carcinomas, one colorectal adenocarcinoma). Two persons with non-bronchogenic carcinomas had identifiable asbestos bodies but no interstitial fibrosis. In two cases the second neoplasms (primary bronchogenic squamous cell and small-cell carcinomas) were associated with diffuse interstitial fibrosis but no asbestos bodies were seen on light microscopy. In each case transmission electron microscopic mineral analysis revealed an asbestos fibre burden within the background population range for control subjects and well below that seen in cases of established asbestosis. These cases were considered to represent cryptogenic fibrosing alveolitis in subjects with a history of asbestos exposure. CONCLUSIONS: Synchronous malignant mesothelioma with carcinomas in asbestos-exposed workers is rare and identified in 1.8% of 500 malignant mesotheliomas in this series. In most cases the carcinoma represents a primary bronchogenic neoplasm. Primary lung carcinomas are recognized to be asbestos related only when occurring in association with asbestosis. In this series this combination (bronchogenic carcinoma and asbestosis) was seen in four (0.8%) cases. In post-mortem cases for possible malignant mesothelioma it is important to identify any other neoplasia and determine whether it is related to asbestos. Their presence impact upon anticipated life expectancy and in the presence of malignant mesothelioma will affect the compensation settlement.

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.

Unusual intraparenchymal growth patterns of malignant pleural mesothelioma.

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

Primary thymic epithelial tumours of the pleura mimicking malignant mesothelioma.

AIMS: To illustrate the macroscopic, light microscopic and immunophenotypic similarities that exist between primary pleural thymic epithelial tumours and diffuse malignant mesothelioma. To investigate the expression of the mesothelial markers, cytokeratin (CK) 5/6, calretinin and thrombomodulin in a series of mediastinal thymic epithelial tumours. METHODS AND RESULTS: Over a 10-year period, 64 diffuse pleural tumours of non-mesothelial histogenesis were identified in the files of referrals to the South Wales regional thoracic centre (Llandough Hospital, Cardiff). Of these, five pleural tumours were diagnosed as primary pleural thymic epithelial neoplasms. From the files of the Mesopath group, Caen, three additional cases of thymic epithelial tumours with pleural involvement were identified. The study group comprised eight cases (four males, four females) with median age at presentation of 56 years (range 19-75 years). In one case there was a history of asbestos exposure. Macroscopically, seven tumours formed diffuse pleural masses. No mediastinal abnormality or intraparenchymal lesions were seen in five cases. By light microscopy, seven thymic epithelial neoplasms showed a lobulated architecture, one appeared extensively cystic. The tumours were of varied morphological subtypes: one medullary (WHO Type A), two mixed (WHO Type AB), three predominantly cortical (WHO Type B1) and two cortical (WHO Type B1). The subtypes morphologically mimicked sarcomatoid, biphasic, lymphohistiocytoid variant and epithelioid mesothelioma. The pleural thymic epithelial tumours showed immunoreactivity with broad spectrum cytokeratin AE1/AE3 (8/8; 100%), CK5/6 (8/8; 100%), and 1/8 (13%) expressed thrombomodulin. Calretinin showed variable nuclear and cytoplasmic expression in all cases, but equivocally in the thymic epithelial cell component. In 7/8 (88%) the thymic epithelial cells exhibited focal aberrant expression of CD20. Epithelial membrane antigen (EMA) showed focal expression in the perivascular and organoid areas in 6/8 (75%) cases. Carcinoembryonic antigen (CEA) and CD34 were uniformly negative. In 4/8 (50%) cases the lymphoid cell component was of immature phenotype expressing CD99, terminal deoxynucleotidyl transferase (TdT) and lymphoid precursors had a high proliferation fraction with Ki67. In the series of 20 primary mediastinal thymic epithelial tumours tested, mesothelial marker expression revealed CK5/6 (20/20), thrombomodulin (3/20; 15%) and calretinin (0/20; 0%). Varying amounts of calretinin-positive stromal cells were present. CONCLUSION: Primary pleural thymic epithelial tumours are rare but may mimic malignant mesothelioma by forming diffuse serosal-based masses. In addition, both tumours may show morphological diversity (with epithelial, spindled and mixed components present). An awareness that thymic epithelial tumours may variably express the mesothelial markers CK5/6, calretinin and thrombomodulin prevents misdiagnosis. In the distinction from malignant mesothelioma a lobulated architecture and organoid features favour a thymic epithelial neoplasm. The presence of aberrant CD20 expression in a cytokeratin-positive epithelial neoplasm and/or the presence of an immature lymphoid population (by demonstration of CD1a, CD2, CD99 and TdT) indicates a thymic epithelial neoplasm. In contrast, nuclear calretinin expression favours malignant mesothelioma.

Value of mesothelial and epithelial antibodies in distinguishing diffuse peritoneal mesothelioma in females from serous papillary carcinoma of the ovary and peritoneum.

AIMS: To evaluate the role of mesothelial markers (calretinin, thrombomodulin, cytokeratin 5/6, and CD44H) and carcinoma markers (polyclonal and monoclonal carcinoembryonic antigen, Leu-M1, CA-125 and Ber-EP4) in distinguishing diffuse peritoneal malignant mesothelioma from primary serous papillary adenocarcinoma of the ovary and peritoneum. METHODS AND RESULTS: Paraffin-embedded formalin-fixed blocks from 32 diffuse peritoneal mesotheliomas of epithelial subtype (all females), 20 serous papillary ovarian carcinomas and three primary peritoneal serous papillary carcinomas were studied. Calretinin and Ber-EP4 appeared to be the best positive mesothelial and carcinoma marker, respectively. Nuclear calretinin expression was identified in 28 of 32 malignant mesotheliomas with no nuclear immunoreactivity in the cohorts of serous papillary ovarian and peritoneal carcinomas, thus yielding 88% sensitivity and 100% specificity. Ber-EP4 showed 95% sensitivity and 91% specificity for serous papillary ovarian carcinoma. Thrombomodulin, cytokeratin 5/6 and CD44H immunoreactivities were seen in 18 (56%), 17 (53%) and 15 (47%) of peritoneal mesotheliomas, respectively, and in six (30%), five (25%) and five (25%) of the ovarian tumours, respectively. None of the three primary peritoneal serous papillary carcinomas expressed calretinin, thrombomodulin, cytokeratin 5/6 or CD44H. Polyclonal and monoclonal CEA, and Leu-M1 were expressed by two (10%), one (5%) and seven (35%) serous papillary ovarian carcinomas, respectively. None of the serous papillary peritoneal carcinomas expressed polyclonal CEA, monoclonal CEA or Leu-M1. CA-125 was positive in 19 (95%) and two (67%) ovarian and peritoneal carcinomas, respectively, and in eight (25%) peritoneal mesotheliomas. CONCLUSIONS: Calretinin and Ber-EP4 are useful discriminant markers in distinguishing peritoneal mesothelioma in women from serous papillary ovarian and peritoneal carcinoma. The other mesothelial markers (thrombomodulin, cytokeratin 5/6, and CD44H) and carcinoma markers (polyclonal and monoclonal CEA, and Leu-M1) yielded a too low sensitivity for practical use.

Prognostic factors in diffuse malignant pleural mesothelioma: effects of pretreatment clinical and laboratory characteristics.

The aim of this study was to investigate the effects of various pretreatment clinical and laboratory characteristics on the survival of patients with diffuse malignant pleural mesothelioma (DMPM). One hundred histopathologically confirmed DMPM patients were evaluated. Fifty-nine were treated with chemoimmunotherapy while 41 who had refused chemoimmunotherapy received supportive therapy alone. The following pretreatment characteristics were evaluated in both univariate and multivariate Cox regression analyses: age, gender, Karnofsky performance score (KPS), histology asbestos exposure, presence of chest pain, dyspnoea, weight loss, symptom duration, smoking history, disease location, platelet count, haemoglobin, white blood cell (WBC) count, serum lactate dehydrogenase (LDH) and extent of disease (stage). Univariate analysis showed that patients with age > or = 75 years, male gender, smoking history advanced stages above stage I disease, KPS < 70, WBC count > or = 8450 and LDH level > or = 500 IU l(-1) have a worse prognosis. With multivariate Cox regression analyses, age > or = 75 years, advanced stages above stage I disease, KPS < 70 and LDH level > or = 500 IU l(-1) were found to be indicators of a poorer prognosis. In conclusion, in our study each of low performance status, older age, advanced stage disease, high LDH level and prognosis were found to be related.

Case-referent survey of young adults with mesothelioma: I. Lung fibre analyses.

OBJECTIVES: Our study aimed to determine the lung tissue concentration of asbestos and other mineral fibres by type and length in persons with mesothelioma aged 50 yr or less at time of diagnosis, compared to controls of similar age and geographical region. In this age group it was thought that most, but not all, work-related exposures would have been since 1970, when the importation of crocidolite, but not amosite, was virtually eliminated. METHODS: Eligible cases were sought from recent reports by chest physicians to the SWORD occupational disease surveillance scheme. Lung tissue samples were obtained at autopsy from 69 male and four female cases, and mineral fibres identified, sized and counted by electron microscopy. Fibre concentrations per microg dry tissue were compared with similar estimates from a control series of autopsies of sudden or accidental deaths. Unadjusted, and adjusted odds ratios calculated by logistic regression, assessed relative risk in relation to fibre type, length and concentration. RESULTS: Unadjusted and adjusted odds ratios increased steadily with concentration of crocidolite, amosite, tremolite and all amphiboles combined. There was also some increase with chrysotile, but well short of statistical significance. Incremental risk examined in a linear model was as highly significant for all amphiboles together as individually. Short, medium and long amphibole fibres were all associated with increased risk in relation to length. Mullite and iron fibres were significant predictors of mesothelioma when considered without adjustment for confounding by amphiboles, but, after adjustment, were weak and far from statistically significant. CONCLUSIONS: In this young age group, amosite and crocidolite fibres could account for about 80% of cases of mesothelioma, and tremolite for some 7%. The contribution of chrysotile, because of low biopersistence, cannot be reliably assessed at autopsy, but to the extent that tremolite is a valid marker, our results suggest that it was small. The steep linear trend in odds ratio shown by amphiboles combined indicates that their effects may be additive, with increased risk from the lowest detectable fibre level. Non-asbestos mineral fibres probably made no contribution to this disease. Contrary to expectation, however, some 90% of cases were in men who had started work before 1970; this was so whether or not amosite or crocidolite was found in lung tissue.

Case-referent survey of young adults with mesothelioma: II. Occupational analyses.

OBJECTIVES: Our study aimed to identify occupations at increased risk of developing mesothelioma in persons aged 50 yr or less, and to relate these occupations to lung tissue concentration of asbestos fibres by type. In this age group it was thought that most, but not all, work-related exposures would have been since 1970, when the importation of crocidolite, but not amosite, was virtually eliminated. METHODS: Eligible cases were sought from recent reports by chest physicians to the SWORD occupational disease surveillance scheme. Work histories were obtained for 115 men and 13 women, usually with the help of the chest physicians or coroners. Jobs were coded by the Office of National Statistics, so that the observed years spent in each occupation could be compared with expected values from census data, 1960-90. Lung tissue samples were obtained at autopsy from 69 male and four female cases, and mineral fibres identified, sized and counted by electron microscopy. RESULTS: Of 37 industrial occupations analysed, odds ratios were significantly raised in eight: five in the construction industry and the others in shipbuilding, the manufacture of cement products and the manufacture of non-metallic mineral products (including asbestos). The concentrations in lung of crocidolite and amosite fibres, which together could account for 80-90% of cases, did not differ between occupational categories; those for amosite were appreciably higher than for crocidolite. Tremolite fibres were rarely found. CONCLUSION: Mesothelioma in this young age group is dominated by carpenters, plumbers, electricians and insulators in the construction industry, and is mainly attributable to amphibole exposure. Work in shipbuilding and manufacture of mineral products was less important than in earlier studies. Contrary to expectation, however, some 90% of cases were in men who had started work before 1970.

p53, p21 and metallothionein immunoreactivities in patients with malignant pleural mesothelioma: correlations with the epidemiological features and prognosis of mesotheliomas with environmental asbestos exposure.

The aim of this study is to investigate immunoreactivity for p53, p21 and metallothionein in diffuse malignant pleural mesothelioma (DMPM) and to determine the relationships between the age, sex, asbestos exposure time, survival of DMPM patients with environmental asbestos exposure and immunoreactivity to p53, p21 and metallothionein. Sixty-seven histopathologically-confirmed DMPMs, 38 of whom had environmental and 29 had occupational asbestos exposure, were included. The tumour tissue samples were immunostained with antibodies against p53, p21 and metallothionein. Epidemiological data and the survival times for the DMPM patients with environmental asbestos exposures were obtained from hospital records. Thirty-three per cent of the DMPMs were positive for p53, 35% for p21 and 52% for metallothionein. There was no statistical difference between the histological subtypes of DMPM in terms of immunoreactivity for p53, p21 and metallothionein. For p21 and metallothionein there was a statistically significant difference between the exposure characteristics: patients with environmental asbestos exposure had shown more immunopositivity. There were statistically significant differences between age groups and between asbestos exposure times for metallothionein, and between asbestos exposure times and p21. The patients with positive immunostaining had longer exposure times and were older than those having negative immunostaining. The differences between survival of the patients were not statistically significant in terms of the immunohistochemical results for p53, p21 and metallothionein.

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

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

Malignant vascular tumours of the pleura in "asbestos" workers and endothelial differentiation in malignant mesothelioma.

BACKGROUND: Three cases of diffuse malignant vascular tumours of the pleura are described which mimicked malignant mesothelioma clinically and pathologically (so called "pseudomesothelioma"). All had occupational histories of exposure to asbestos. The relationship of these tumours to mesothelioma and asbestos exposure is discussed. METHODS: To examine the histogenetic relationship between mesothelioma and these three tumours an immunohistochemical analysis of vascular marker (CD31, CD34, and Von Willebrand factor) expression was undertaken in 92 cases of pleural mesothelioma, in addition to these three tumours. Electron microscopic fibre analysis of lung tissue was performed on each of the three cases to assess asbestos fibre content. RESULTS: Diffuse pleural epithelioid haemangioendotheliomas may closely resemble malignant mesothelioma clinically and pathologically but, of the 92 pleural mesotheliomas tested, none showed expression of CD31, CD34, and Von Willebrand factor. Although all three cases had claimed exposure to asbestos, ferruginous bodies typical of asbestos were only seen by light microscopy in case 2, and only in this subject was the asbestos fibre content raised in comparison with the range seen in a non-exposed background population. The latent period in the pleural epithelioid haemangioendotheliomas ranged from 18 to 60 years. CONCLUSIONS: Endothelial differentiation does not appear to occur in mesothelioma and therefore should be clearly separated from it. No definite association between pleural epithelioid haemangioendothelioma and exposure to asbestos can be made from this small series but further investigation is warranted.

The separation of benign and malignant mesothelial proliferations.

The separation of benign from malignant mesothelial proliferations has emerged as a major problem in the pathology of the serosal membranes. For both epithelial and spindle cell mesothelial processes, true stromal invasion is the most accurate indicator of malignancy, but stromal invasion is often difficult to assess, especially in small biopsies. In the pleural cavity, deep penetration of a thickened and fibrotic pleura or penetration of mesothelial cells into the fat of the chest wall are good indicators of malignancy; however, superficial entrapment of mesothelial cells and glands by organizing effusions is common in benign reactions and needs to be distinguished from invasion. In the peritoneal cavity, invasion of fat or of organ walls is again the most reliable indicator of malignancy, but entrapment of benign cells in organizing granulation tissue or between fat lobules is frequent and confusing. Proliferations confined to the pleural or peritoneal space, particularly linear arrays of atypical mesothelial cells on the free surface, should not be called malignant in the absence of unequivocal invasion. Cytologic atypia is often not helpful in separating benign from malignant reactions, because benign processes are commonly atypical and mesotheliomas are often deceptively monotonous. Densely packed mesothelial cells within the pleural space are frequent in benign reactions, but densely packed mesothelial cells within the stroma favor a diagnosis of malignancy. Organizing effusions (fibrous pleurisy) typically show zonation with high cellularity and cytologic atypia toward the pleural space and increasing fibrosis with decreasing cellularity and lesser atypia toward the chest wall, whereas sarcomatous (including desmoplastic) mesotheliomas do not demonstrate this type of zonation. Elongated capillaries perpendicular to the pleural surface are seen in organizing effusions but are not a feature of sarcomatous mesotheliomas. The combination of a paucicellular storiform pattern, plus invasion of the stroma (including fat and adjacent tissues), or bland necrosis, overtly sarcomatous foci, or distant metastases, is required for the diagnosis of desmoplastic mesothelioma. Necrosis is usually a sign of malignancy but is occasionally seen in benign mesothelial reactions. Keratin staining is useful in indicating the distribution of mesothelial cells, and particularly in demonstrating penetration of mesothelial cells into the stroma or adjacent structures, but is of no help in separating benign and malignant proliferations because both are keratin-positive. Although both p53 and EMA staining have been proposed as markers of mesothelial malignancy, in our experience they are not helpful for the individual case.