Application of immunohistochemistry to the diagnosis of malignant mesothelioma

Adenocarcinoma cells in effusion cytology as a diagnostic pitfall with potential impact on clinical management: a case report with brief review of immunomarkers

Distinguishing metastatic carcinoma cells from reactive mesothelial cells in effusion samples is often challenging based on morphology alone. Metastatic carcinoma cells in fluid samples may mimic reactive mesothelial cells due to overlapping cytological features. We report a case of a pleural effusion in a 51-year-old female patient with a medical history significant for bilateral ovarian tumors and peritoneal implants diagnosed as serous tumor of borderline malignant potential. The effusion was composed almost entirely of adenocarcinoma cells that morphologically mimicked reactive mesothelial cells. The diagnosis of metastatic adenocarcinoma was made after a wide immunostaining panel of antibodies. Recognizing metastatic adenocarcinoma cells in effusion samples can be challenging and an accurate diagnosis may have significant impact on clinical management as demonstrated by this case.

Immunoreactivity for calretinin and keratins in desmoid fibromatosis and other myofibroblastic tumors: a diagnostic pitfall

Calretinin is an intracellular calcium-binding EF-hand protein of the calmodulin superfamily. It plays a role in diverse cellular functions, including message targeting and intracellular calcium signaling. It is expressed in the mesothelium, mast cells, some neural cells, and fat cells, among others. Because of its relative specificity for mesothelial neoplasms, calretinin is widely used as one of the primary immunohistochemical markers for malignant mesothelioma and in differentiating it from adenocarcinoma. On the basis of our sporadic observation on calretinin immunoreactivity in desmoid fibromatosis, we systematically evaluated calretinin, keratin cocktail (AE1/AE3), and WT1 immunoreactivity in 268 fibroblastic/myofibroblastic neoplasms. Calretinin was observed in 75% (44/58) of desmoid fibromatosis, 50% (21/42) of proliferative fasciitis, 23% (8/35) of nodular fasciitis, 33% (13/40) of benign fibrous histiocytoma, 35% (22/62) of malignant fibrous histiocytoma, and 13% (4/31) of solitary fibrous tumors but not in normal connective tissue fibroblasts at various sites. Keratin AE1/AE3 immunoreactivity was also commonly (6/13) present in the large ganglion-like cells of proliferative fasciitis and sometimes in nodular fasciitis (3/35), solitary fibrous tumor (3/27), and malignant fibrous histiocytoma (9/62). Nuclear immunoreactivity for WT1 or keratin 5 positivity was not detected in myofibroblastic tumors. On the basis of these observations, it can be concluded that calretinin and focal keratin immunoreactivity is fairly common in benign and malignant fibroblastic and myofibroblastic lesions. Calretinin-positive and keratin-positive spindle cells in desmoid and nodular fasciitis or calretinin-positive ganglion-like cells in proliferative fasciitis should not be confused with elements of epithelioid or sarcomatoid mesothelioma. These diagnostic pitfalls can be avoided with careful observation of morphology, quantitative differences in keratin expression, and use of additional immunohistochemical markers such keratin 5 and WT1 to verify true epithelial and mesothelial differentiation typical of mesothelioma.

Diffuse Malignant Mesothelioma

Diffuse malignant mesothelioma (DMM) is an uncommon cancer with great clinical significance because it currently remains an incurable disease, and most patients die within months after diagnosis. Although DMM incidence is leveling off or decreasing in developed countries because of the strict control of asbestos use, it is increasing in countries without adequate asbestos control. In some settings, benign, reactive mesothelial hyperplasias and organizing pleuritis can be difficult to differentiate from DMM and vice versa, and the variety of DMM's histopathologic features generates an extensive list of differential diagnoses with other malignancies, particularly, metastatic malignancies, which are more frequent in the pleura than are primary malignancies. These two issues are the topic of discussion in this review, along with a brief presentation of a case of DMM that presented in a 66-year-old man with recurrent, right pleural effusions, and in whom, diagnosis of DMM had not been suspected clinically, radiographically, surgically, grossly, or initially, on frozen section. It was not until focal invasion into the skeletal muscle was discovered on permanent sections that a diagnosis of DMM could be established.

Utility of Glucose Transporter 1 in the Distinction of Benign and Malignant Thoracic and Abdominal Mesothelial Lesions

Context.—Malignant mesothelioma, of either peritoneum or pleura, is an uncommon cancer. The diagnosis is often difficult to make, in part because of the overlapping morphology of reactive and malignant mesothelial cells. Glucose transporter 1 (GLUT-1) is a glucose transporter typically found on erythrocytes, which is aberrantly expressed in various carcinomas. It has recently been reported as specific and sensitive in discriminating malignant pleural mesothelioma from reactive hyperplasia. The application of GLUT-1 staining in peritoneal mesothelioma has not been fully explored.

Objective.—To determine if GLUT-1 staining is helpful in distinguishing abdominal mesotheliomas from benign, reactive mesothelial lesions and to further study its utility in the thorax.

Design.—Tissue microarrays containing 135 abdominal malignant mesotheliomas and 30 malignant pleural mesotheliomas were stained with an antibody to GLUT-1, as were 56 reactive mesothelial lesions.

Results.—The overall sensitivity and specificity for GLUT-1 in mesothelioma was 53% and 98%, respectively. The sensitivity in epithelioid malignant mesothelioma was 49% and in sarcomatoid/biphasic malignant mesothelioma, 66%. In the thorax, the sensitivity was 50% and in the abdomen it was 54%. The positive predictive value of GLUT-1 immunoreactivity was 98% and the negative predictive value was 40%.

Conclusion.—Glucose transporter 1 staining of thoracic mesotheliomas showed high specificity but lower sensitivity than previously reported. Abdominal malignant mesotheliomas showed similar results. Because of low sensitivity, only positive staining is informative. In both sites, the utility of the stain was limited by nonspecific staining (eg, in necrotic areas) as well as bright labeling of erythrocytes and occasional lymphoid elements. Despite these limitations, GLUT-1 can help differentiate malignant mesothelioma from reactive benign mesothelium.

Malignant peritoneal mesothelioma presenting with persistent high fever

Malignant peritoneal mesothelioma (MPM) is a rare tumor that develops in the peritoneum. In this paper, we describe an extremely rare case of MPM metastasizing to the appendix in a 48-year-old female who initially presented with a persistent high fever. The woman reported a slight lower abdominal discomfort which had been relieved by urination for four months. She had lost 5 kg of weight. There was no nausea, vomiting, diarrhea, abdominal pain, or abdominal distension. Many broad spectrum antibiotics were given without relief of fever. Computed tomography (CT) scans revealed a thickened omentum majus and diffused multiple omental nodules. An omentectomy, appendectomy, and adnexectomy were carried out. A gross pathologic specimen of omentum tissue revealed a firm gray-white mass. Microscopic and immunohistochemical examinations confirmed the diagnosis of appendiceal and bilateral adnexal metastases of an MPM. These results suggest that MPM should be considered in the differential diagnosis of unexplained persistent high fever. Awareness of such atypical presentations of mesothelioma may help to make a correct diagnosis.

Expression of the Ets transcription factor EHF in serous ovarian carcinoma effusions is a marker of poor survival

The EHF (Ets homologous factor) gene was previously shown to be overexpressed in ovarian/primary peritoneal serous carcinoma compared to malignant mesothelioma using gene expression arrays. The objective of this study was to validate this finding at the mRNA level in a larger series. We analyzed the diagnostic role of EHF in 98 ovarian serous carcinoma effusions, 23 malignant mesothelioma specimens (20 effusions, 3 surgical specimens), and 28 primary ovarian serous carcinomas using quantitative real-time polymerase chain reaction. Expression levels of EHF in ovarian carcinoma were additionally investigated for association with clinicopathologic parameters and survival. Quantitative real-time polymerase chain reaction analysis showed significantly higher expression of EHF mRNA in ovarian carcinoma effusions and in primary ovarian carcinoma compared to malignant mesothelioma effusions (P < .001 for both). EHF mRNA expression was additionally higher in primary ovarian carcinomas compared to effusions of this cancer (P < .001). In univariate analysis for all patients with effusions, higher EHF mRNA levels were associated with a trend for shorter progression-free survival (P = .066), which became significant in analysis of 45 patients with primary diagnosis pre-chemotherapy effusions (P = .01). In Cox multivariate analysis, EHF mRNA expression was an independent predictor of poor progression-free survival for all patients and patients with primary diagnosis pre-chemotherapy effusions (P = .033 and P = .009, respectively). EHF mRNA levels differentiate ovarian carcinoma from malignant mesothelioma and may thus be of diagnostic value in this setting. EHF may be a novel prognostic marker in ovarian carcinoma.

Novel platelet activation receptor CLEC-2: from discovery to prospects

C-type lectin-like receptor 2 (CLEC-2) has been identified as a receptor for the platelet activating snake venom rhodocytin. CLEC-2 elicits powerful platelet activation signals in conjunction with Src, Syk kinases, and phospholipase Cγ2, similar to the collagen receptor glycoprotein (GP) VI/FcRγ-chain complex. In contrast to GPVI/FcRγ, which initiates platelet activation through the tandem YxxL motif immunoreceptor tyrosine-based activation motif (ITAM), CLEC-2 signals via the single YxxL motif hemi-ITAM. The endogenous ligand of CLEC-2 has been identified as podoplanin, which is expressed on the surface of tumour cells and facilitates tumour metastasis by inducing platelet activation. Studies of CLEC-2-deficient mice have revealed several physiological roles of CLEC-2. Podoplanin is also expressed in lymphatic endothelial cells as well as several other cells, including type I alveolar cells and kidney podocytes, but is absent from vascular endothelial cells. In the developmental stages, when the primary lymph sac is derived from the cardinal vein, podoplanin activates platelets in lymphatic endothelial cells by binding to CLEC-2, which facilitates blood/lymphatic vessel separation. Moreover, CLEC-2 is involved in thrombus stabilisation under flow conditions in part through homophilic interactions. However, the absence of CLEC-2 does not significantly increase bleeding tendency. CLEC-2 may be a good target protein for novel anti-platelet drugs or anti-metastatic drugs having therapeutic and preventive effects on arterial thrombosis and cancer, the primary causes of mortality in developed countries. In this article, we review the mechanisms of signal transduction, structure, expression, and function of CLEC-2.

PINCH-2 expression in cancers involving serosal effusions using quantitative PCR

OBJECTIVE

The PINCH-2 gene was previously shown to be overexpressed in malignant mesothelioma compared with ovarian/peritoneal serous carcinoma in Affymetrix array analysis. The objective of the present study was to validate this finding at the mRNA and protein level.

METHODS

Effusions (n = 91; 71 ovarian and 10 breast carcinomas, 10 malignant mesotheliomas) were assayed for PINCH-2 mRNA expression using quantitative PCR. PINCH-2 protein expression was analysed in 37 effusions using flow cytometry.

RESULTS

Quantitative PCR analysis showed significantly higher PINCH-2 mRNA levels in mesotheliomas compared with carcinomas (P = 0.004). Values of <10 copies were found exclusively in carcinoma effusions (25.4% of ovarian and 50% of breast carcinomas). However, PINCH-2 protein expression by flow cytometry did not differ significantly between the three cancer types. No association was observed between PINCH-2 levels and patient survival or expression of previously-studied molecules related to adhesion, metastasis and apoptosis inhibition in ovarian carcinoma.

CONCLUSIONS

Our data suggest that PINCH-2 mRNA is overexpressed in malignant mesothelioma compared with carcinomas involving serosal cavities, and that low levels of this gene argue against the diagnosis of mesothelioma. The frequent PINCH-2 protein expression in all three studied cancers suggests a role for this molecule in cancer cell biology in effusions and merits further research.

Multimodality Imaging Review of Malignant Pleural Mesothelioma Diagnosis and Staging

Early diagnosis and accurate disease staging in patients with malignant pleural mesothelioma (MPM) are essential in classifying such patients into prognostic subgroups to allow delivery of stage-specific therapies. This review addresses the current status of multimodality imaging in the diagnosis and staging of MPM. Clinical, research, and future directions in computed tomography (CT), magnetic resonance imaging, and PET/CT diagnosis and staging of MPM are discussed, including the use of novel PET probes. The article concludes with important take-home messages summarized as the pearls and pitfalls of each diagnostic modality in the diagnosis and staging of patients with MPM.

Lymphatic differentiation in classic Kaposi's sarcoma: patterns of D2-40 immunoexpression in the course of tumor progression

The recent development of lymphatic endothelium-specific immuno-indicators has given rise to research on the histogenesis of Kaposi sarcoma (KS), specifically focusing on its lymphatic root and differentiation. D2-40 is a new lymphatic marker that recognizes podoplanin and is easily applied to formalin-fixed paraffin-embedded human tissues. This study examined D2-40 immunoexpression in 178 classical KS lesions using immunohistochemical methods. D2-40 immunoexpression was also examined in 63 non-KS soft tissue lesions to test the reliability of D2-40 monoclonal antibody in the pathological diagnosis of KS. D2-40 immunoreactivity was detected at all of the KS lesions and in lymphangioma and nonneoplastic lymphatic endothelium. There was no significant relationship between the extent of D2-40 staining and histopathological stage; however, there was a positive correlation between the staining intensity and histopathological stage in KS cases. D2-40 immunoreactivity was detected at all histopathological stages of KS and may be added to the routine immunohistochemical panel used for the differential diagnosis of KS. Widespread D2-40 protein expression is evidence of a lymphatic origin or the differentiation of neoplastic cells in KS, and D2-40 expression increases with tumor progression.

Expert opinions of the first italian consensus conference on the management of malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a very important public health issue. A large amount of data indicates a relationship between mesothelioma and asbestos exposure. The incidence has both considerably and constantly increased over the past 2 decades in the industrialized countries and is expected to peak in 2010-2020. In Italy, a standardized-rate incidence in 2002 among men was 2.98 per 100,000 and 0.98 per 100,000 among women, with wide differences from one region to another. Stage diagnosis and definition may be difficult. Management of patients with MPM remains complex, so an optimal treatment strategy has not yet been clearly defined. The First Italian Consensus Conference on Malignant Pleural Mesothelioma was held Bologna (Italy) in May 20, 2008. The Consensus Conference was given the patronage of the Italian scientific societies AIOM, AIRO, AIPO, SIC, SICO, SICT, SIAPEC-IAP, AIOT, GOAM, and GIME. This Consensus did not answer all of the unresolved questions in MPM management, but the Expert Opinions have nonetheless provided recommendations, presented in this report, on MPM management for clinicians and patients.

[TTF-1: neither angel nor demon]

Expressed in thyroid, lung and diencephalon, the Thyroid transcription factor-1 (TTF-1) regulates, in these organs, the transcription of specific genes. This review focuses on the use of TTF-1 as a diagnostic tool in thyroid and lung carcinomas. According to the literature, TTF-1 seems to be involved in aggressive relapses. In some cases it could be also involved in the remission. The use of TTF-1 as a prognostic tool for some neoplasms is discussed.

The development and characterization of a human mesothelioma in vitro 3D model to investigate immunotoxin therapy

Background

Tumor microenvironments present significant barriers to penetration by antibodies and immunoconjugates. Tumor microenvironments, however, are difficult to study in vitro. Cells cultured as monolayers exhibit less resistance to therapy than those grown in vivo and an alternative research model more representative of the in vivo tumor is more desirable. SS1P is an immunotoxin composed of the Fv portion of a mesothelin-specific antibody fused to a bacterial toxin that is presently undergoing clinical trials in mesothelioma.

Methodology/Principal Findings

Here, we examined how the tumor microenvironment affects the penetration and killing activity of SS1P in a new three-dimensional (3D) spheroid model cultured in vitro using the human mesothelioma cell line (NCI-H226) and two primary cell lines isolated from the ascites of malignant mesothelioma patients. Mesothelioma cells grown as monolayers or as spheroids expressed comparable levels of mesothelin; however, spheroids were at least 100 times less affected by SS1P. To understand this disparity in cytotoxicity, we made fluorescence-labeled SS1P molecules and used confocal microscopy to examine the time course of SS1P penetration within spheroids. The penetration was limited after 4 hours. Interestingly, we found a significant increase in the number of tight junctions in the core area of spheroids by electron microscopy. Expression of E-Cadherin, a protein involved in the assembly and sealing of tight junctions and highly expressed in malignant mesothelioma, was found significantly increased in spheroids as compared to monolayers. Moreover, we found that siRNA silencing and antibody inhibition targeting E-Cadherin could enhance SS1P immunotoxin therapy in vitro.

Conclusion/Significance

This work is one of the first to investigate immunotoxins in 3D tumor spheroids in vitro. This initial description of an in vitro tumor model may offer a simple and more representative model of in vivo tumors and will allow for further investigations of the microenvironmental effects on drug penetration and tumor cell killing. We believe that the methods developed here may apply to the studies of other tumor-targeting antibodies and immunoconjugates in vitro.

Mesothelial proteins are expressed in the human cornea

The goal of our study was to determine whether proteins typical of the human mesothelial cell phenotype, such as mesothelin, HBME-1 (Hector Battifora mesothelial cell-1) protein and calbindin 2, are expressed in the human cornea, especially in endothelial cells. Cryosections and endothelial and epithelial imprints of sixteen human cadaverous corneoscleral discs were used. The presence of proteins was examined using immunohistochemistry and Western blotting, while mRNA levels were determined by qRT-PCR. A strong signal for mesothelin was present in the corneal epithelium, while less intense staining was visible in the endothelium. Similarly, higher and lower mRNA levels were detected using qRT-PCR in the corneal epithelium and endothelium, respectively. HBME-1 antibody strongly stained the corneal endothelium and stromal keratocytes. Marked positivity was present in the corneal stromal extracellular matrix, while no staining was present in the sclera. Calbindin 2 was detected using immunohistochemistry and Western blotting in the corneal epithelium, endothelium and stroma. qRT-PCR confirmed its expression in epithelial and endothelial cells. Three proteins expressed constitutively in mesothelial cells were detected in the human cornea. The possible function of mesothelin in cell-cell contact on the ocular surface is discussed. The presence of HBME-1 protein in the endothelial layer may indicate a still unknown function that could be shared with mesothelial cells of the pleura and peritoneum. The much more pronounced occurrence of calbindin 2 in the corneal epithelium compared to fewer positive endothelial cells explains the higher turnover of epithelial cells compared to the proliferatively inactive endothelium.

Podoplanin is a useful marker for identifying mesothelioma in malignant effusions

The diagnosis of malignant mesothelioma in serosal effusions continues to be a major challenge because some of its cytomorphological features closely resemble adenocarcinomas. Immunohistochemistry is a valuable tool in the differentiation of epithelioid mesothelioma from metastatic adenocarcinomas. However, no single antibody has demonstrated absolute sensitivity or specificity. In this study, we evaluated the value of immunostaining pattern for podoplanin to differentiate mesothelioma from adenocarcinomas of various origins.Cell blocks from previously collected paraffin-embedded cell blocks of 86 effusions (18 mesothelioma, 35 reactive mesothelium, 9 breast adenocarcinoma, 14 ovarian adenocarcinoma, and 10 lung adenocarcinoma) were retrieved from the file of the Department of Pathology at University of Michigan and Lund University in Sweden and were used for the study. Slides prepared from the cell blocks were stained for podoplanin. The percentage of immunostained cells was recorded as follows: 1+ (5-25%), 2+ (26-50%), and 3+ (>50%). A stain result involving <5% of cells was considered negative. The intensity of positive results was evaluated as strong, moderate, or weak.Podoplanin is expressed in 94% of malignant mesothelioma cases (17/18), 97% (30/31) of cases of reactive mesothelial, 0% of lung adenocarcinoma cases (0/9), 0% of breast adenocarcinoma (0/9), and 7% of ovarian adenocarcinoma (1/14). All positive cases of malignant mesothelioma and reactive mesothelium showed strong membranous reactivity to podoplanin. The one positive case of ovarian adenocarcinoma showed a weak membranous podoplanin immunostaining.On the basis of our results and published data, we believe that membranous podoplanin immunoreactivity, in conjunction with calretinin, would be more specific than CK5/6 and WT-1 in differentiating epithelioid malignant mesothelioma from adenocarcinoma of the lung, breast, and ovary.

Benign and Malignant Mesothelial Proliferation

Malignant mesothelioma (MM) is a rare primary malignant tumor of the surface serosal cells. The diagnosis of MM is challenging with a broad differential diagnosis. For many decades, studies have focused on distinguishing MM from other types of cancer; however, benign mesothelial cell hyperplasia, especially in small biopsies, has emerged as a major problem. The features of pleural lesions are somewhat different from peritoneal diseases, and this article primarily focuses on pleural diseases. Thorough interpretation and correlation of clinical, radiologic, and pathologic findings are essential for a correct diagnosis.

Diagnosis of metastatic neoplasms: an immunohistochemical approach

CONTEXT

It is important to determine the type and/or site of origin of metastatic tumors for optimal clinical management.

OBJECTIVE

To summarize the use of currently available immunohistochemical markers in the evaluation of metastatic tumors.

DATA SOURCES

Review of relevant literature on immunohistochemical evaluation of tumors and the author's personal experience.

CONCLUSIONS

Immunohistochemistry is an important ancillary technique for evaluation of metastatic tumors and should be used in the context of routine morphology and clinical information. While a single marker may be used to support a known or suspected site of origin, a carefully constructed panel is strongly recommended, particularly for tumors of morphologically uncertain lineage or origin.

Diagnosis of Metastatic Neoplasms: A Clinicopathologic and Morphologic Approach

Context.—The diagnosis of the site of origin of metastatic neoplasms often poses a challenge to practicing pathologists. A variety of immunohistochemical and molecular tests have been proposed for the identification of tumor site of origin, but these methods are no substitute for careful attention to the pathologic features of tumors and their correlation with imaging findings and other clinical data. The current trend in anatomic pathology is to overly rely on immunohistochemical and molecular tests to identify the site of origin of metastatic neoplasms, but this “shotgun approach” is often costly and can result in contradictory and even erroneous conclusions about the site of origin of a metastatic neoplasm.

Objective.—To describe the use of a systematic approach to the evaluation of metastatic neoplasms.

Data Sources.—Literature review and personal experience.

Conclusions.—A systematic approach can frequently help to narrow down differential diagnoses for a patient to a few likely tumor sites of origin that can be confirmed or excluded with the use of selected immunohistochemistry and/or molecular tests. This approach involves the qualitative evaluation of the “pretest and posttest probabilities” of various diagnoses before the immunohistochemical and molecular tests are ordered. Pretest probabilities are qualitatively estimated for each individual by taking into consideration the patient's age, sex, clinical history, imaging findings, and location of the metastases. This estimate is further narrowed by qualitatively evaluating, through careful observation of a variety of gross pathology and histopathologic features, the posttest probabilities of the most likely tumor sites of origin. Multiple examples of the use of this systematic approach for the evaluation of metastatic lesions are discussed.

Tenascin-X is a novel diagnostic marker of malignant mesothelioma

Tenascin XB (TNXB) was previously identified as a gene that is more highly expressed in malignant mesothelioma compared with ovarian/peritoneal serous carcinoma based on gene expression array analysis. The objective of this study was to validate this finding at the mRNA and protein levels. Effusions (n = 91; 71 ovarian carcinomas, 10 breast carcinomas, and 10 malignant mesotheliomas) were assayed for TNXB mRNA expression using quantitative polymerase chain reaction. Tenascin-X protein expression was studied in 183 effusions (137 carcinomas of different origin, 37 mesotheliomas, and 9 reactive effusions) and 178 solid lesions (122 ovarian/peritoneal carcinomas and 56 mesotheliomas) using immunohistochemistry. Quantitative polymerase chain reaction analysis showed significantly higher TNXB mRNA level in mesotheliomas compared with ovarian and breast carcinomas (P < 0.001). By immunohistochemistry, tenascin-X protein expression was significantly higher in malignant mesothelioma compared with metastatic carcinoma in effusions (34 of 37 vs. 31 of 137 positive cases; sensitivity = 92% and specificity = 77%; P < 0.001). Reactive mesothelial cells had focal or no tenascin-X expression. Tenascin-X protein was detected in 41 of 56 mesothelioma biopsy specimens and was uniformly absent from all 122 ovarian carcinomas (sensitivity = 73% and specificity = 100%; P < 0.001). Our data suggest that tenascin-X may be a new diagnostic marker of malignant mesothelioma in the differential diagnosis of cancers involving the serosal cavities, particularly in the differential diagnosis between this tumor and ovarian/peritoneal serous carcinoma.

Improving the outcome in malignant pleural mesothelioma: nonaggressive or aggressive approach?

PURPOSE OF REVIEW

The treatment of malignant pleural mesothelioma continues to be a clinical challenge. The question, however, is no longer whether to provide active treatment or not, but how aggressive the treatment should be in view of the limited life expectancy of patients with this disease.

RECENT FINDINGS

With platin and pemetrexed-based combination chemotherapy having become the preferred systemic therapy, the major questions now evolve around the identification of a suitable second line therapy and the quest for innovative new approaches. Surgical interventions from pleurectomy and decortication to extrapleural pneumonectomy have increasingly come of use in specialized centres. With neoadjuvant chemotherapy and extrapleural pneumonectomy median survival times of almost 2 years have been reported. Studies on high-dose hemithoracic radiotherapy after extrapleural pneumonectomy suggested a beneficial effect on local recurrence. However, both extrapleural pneumonectomy and high-dose hemithoracic radiotherapy are associated with potential treatment-related mortality and morbidity and cannot yet be recommended outside specialized centres.

SUMMARY

More than ever, the diagnosis and treatment of patients with malignant pleural mesothelioma mandate a multidisciplinary approach.

Adenomatoid tumors of the female and male genital tracts: a clinicopathological and immunohistochemical study of 44 cases

Adenomatoid tumors of the female and male genital tracts are well characterized as mesothelial in origin, but a detailed histological and immunohistochemical analysis comparing both traditional and newer mesothelial markers across gender and site has not been formally conducted. A variety of morphologic features previously described as characteristic of adenomatoid tumors were evaluated in 44 adenomatoid tumors from the male and female genital tracts. Immunohistochemical analysis with pankeratin (AE1/CAM5.2), WT-1, calretinin, CK5/6, D2-40, and caldesmon was also performed. The extent and intensity of staining were scored semiquantitatively on one representative section per case and mean value for each parameter was calculated. All (n=44) the adenomatoid tumors from both the female and male genital tracts demonstrated a distinctive thread-like bridging strand pattern. Lymphoid aggregates were seen in all 12 adenomatoid tumors of male patients, but in only 4 of 32 (13%) tumors in female patients (P<0.0001). The remaining morphologic features were variably present with no clear sex predilection. Pankeratin, calretinin, and D2-40 reactivity were identified in all female (n=32) and male (n=12) genital tract adenomatoid tumors. Adenomatoid tumors expressed WT-1 in 11/12 (92%) male patients and in 31/32 (97%) female patients. In male patients, reactivity for CK5/6 and caldesmon was found in 1/12 (8%) and 0/12 (0%) adenomatoid tumors (respectively), whereas reactivity in female patients was found in 5/32 (16%) and 1/32 (3%); respectively. Female tumors differ from their male counterparts by the frequent absence of lymphoid aggregates and the presence of a circumscribed margin when occurring in the fallopian tube. Of the putative mesothelial markers evaluated, calretinin, D2-40, and WT-1 show a similar immunoprofile and have a higher sensitivity than CK5/6 and caldesmon in genital tract adenomatoid tumors. However, the presence of additional, often strong expression of WT-1 in normal tissues of the female genital tract limits the utility of WT-1 in this setting.

Differentiation of lung adenocarcinoma, pleural mesothelioma, and nonmalignant pulmonary tissues using DNA methylation profiles

Pathologic differentiation of tissue of origin in tumors found in the lung can be challenging, with differentiation of mesothelioma and lung adenocarcinoma emblematic of this problem. Indeed, proper classification is essential for determination of treatment regimen for these diseases, making accurate and early diagnosis critical. Here, we investigate the potential of epigenetic profiles of lung adenocarcinoma, mesothelioma, and nonmalignant pulmonary tissues (n = 285) as differentiation markers in an analysis of DNA methylation at 1413 autosomal CpG loci associated with 773 cancer-related genes. Using an unsupervised recursively partitioned mixture modeling technique for all samples, the derived methylation profile classes were significantly associated with sample type (P < 0.0001). In a similar analysis restricted to tumors, methylation profile classes significantly predicted tumor type (P < 0.0001). Random forests classification of CpG methylation of tumors--which splits the data into training and test sets--accurately differentiated mesothelioma from lung adenocarcinoma over 99% of the time (P < 0.0001). In a locus-by-locus comparison of CpG methylation between tumor types, 1266 CpG loci had significantly different methylation between tumors following correction for multiple comparisons (Q < 0.05); 61% had higher methylation in adenocarcinoma. Using the CpG loci with significant differential methylation in a pathway analysis revealed significant enrichment of methylated gene-loci in Cell Cycle Regulation, DNA Damage Response, PTEN Signaling, and Apoptosis Signaling pathways in lung adenocarcinoma when compared with mesothelioma. Methylation profile-based differentiation of lung adenocarcinoma and mesothelioma is highly accurate, informs on the distinct etiologies of these diseases, and holds promise for clinical application.

Malignant pleural mesothelioma

Malignant pleural mesothelioma continues to be a challenge. The diagnosis and treatment of patients with malignant pleural mesothelioma requires a multidisciplinary approach. The diagnosis is best made by thoracoscopic biopsy and the aid of immunohistochemistry. Molecular studies identified inactivation of the neurofibromatosis-2 gene and INK4alpha/ARF to be key events in tumorigenesis. Based on the results of a Phase III trial, the combination of cisplatin with pemetrexed has become the preferred choice for chemotherapy, although there is suggestive evidence for the activity of other platin combinations based on Phase II studies. The optimal second-line chemotherapy remains to be defined. Surgical interventions ranging from pleurectomy/decortication to extrapleural pneumonectomy are increasingly offered in specialized centers, and the results of multimodality approaches with neoadjuvant or adjuvant chemotherapy and extrapleural pneumonectomy are encouraging. Ongoing investigations are defining the role of postoperative radiotherapy and the clinical activity of tyrosine kinase inhibitors targeting VEGFR2, histone deacetylase inhibitors and proteosome inhibitors.

Pathologic evaluation of unknown primary cancer

The pathologic approach to metastases of unknown primary cancer (UPC) is stepwise and uses the clinical context, morphology, and, where necessary, immunohistochemistry (IHC). This review covers the initial approach to a UPC biopsy; the diagnosis of malignancy and broad tumor typing into carcinoma, melanoma, lymphoma, or sarcoma; and further subtyping of carcinoma into germ cell (broadly included), squamous, neuroendocrine, and solid organ including liver and renal, and adenocarcinomas. Finally, for adenocarcinoma, the prediction of primary tumor site, including lung, pancreas, stomach, colon, ovary, prostate, and breast, is discussed. For each tumor type, the morphologic features are presented alongside established useful IHC markers, with a description of their staining patterns and common diagnostic dilemmas. Optimal tissue handling and IHC interpretation, quality assurance, and limitations also are discussed. The target readership is oncologists, but other clinicians and trainee pathologists also may find the content of use.

Molecular Basis of Pulmonary Disease

Pulmonary pathology includes a large spectrum of both neoplastic and non-neoplastic diseases that affect the lung. Many of these are a result of the unusual relationship of the lung with the outside world. Every breath that a human takes brings the outside world into the body in the form of infectious agents, organic and inorganic particles, and noxious agents of all types. Although the lung has many defense mechanisms to protect itself from these insults, these are not infallible; therefore, lung pathology arises. Damage to the lung is particularly important given the role of the lung in the survival of the organism. Any impairment of lung function has widespread effects throughout the body, since all organs depend on the lungs for the oxygen they need. Pulmonary pathology catalogs the changes in the lung tissues and the mechanisms through which these occur. This chapter presents a review of lung pathology and the current state of knowledge about the pathogenesis of each disease. It suggests that a clear understanding of both morphology and mechanism is required for the development of new therapies and preventive measures.

Malignant mesothelioma

Malignant mesothelioma is a fatal asbestos-associated malignancy originating from the lining cells (mesothelium) of the pleural and peritoneal cavities, as well as the pericardium and the tunica vaginalis. The exact prevalence is unknown but it is estimated that mesotheliomas represent less than 1% of all cancers. Its incidence is increasing, with an expected peak in the next 10–20 years. Pleural malignant mesothelioma is the most common form of mesothelioma. Typical presenting features are those of chest pain and dyspnoea. Breathlessness due to a pleural effusion without chest pain is reported in about 30% of patients. A chest wall mass, weight loss, sweating, abdominal pain and ascites (due to peritoneal involvement) are less common presentations. Mesothelioma is directly attributable to occupational asbestos exposure with a history of exposure in over 90% of cases. There is also evidence that mesothelioma may result from both para-occupational exposure and non-occupational "environmental" exposure. Idiopathic or spontaneous mesothelioma can also occur in the absence of any exposure to asbestos, with a spontaneous rate in humans of around one per million. A combination of accurate exposure history, along with examination radiology and pathology are essential to make the diagnosis. Distinguishing malignant from benign pleural disease can be challenging. The most helpful CT findings suggesting malignant pleural disease are 1) a circumferential pleural rind, 2) nodular pleural thickening, 3) pleural thickening of > 1 cm and 4) mediastinal pleural involvement. Involvement of a multidisciplinary team is recommended to ensure prompt and appropriate management, using a framework of radiotherapy, chemotherapy, surgery and symptom palliation with end of life care. Compensation issues must also be considered. Life expectancy in malignant mesothelioma is poor, with a median survival of about one year following diagnosis.

Problems in mesothelioma diagnosis

Many centres are now seeing increasing numbers of patients with malignant mesothelioma. This presents pathologists involved in making the diagnosis with a number of problems, which can be divided into those encountered in making the distinction between mesothelioma and benign changes and those experienced in separating mesotheliomas from other types of epithelial and connective tissue tumours. Immunohistochemistry plays a major role in helping to make the diagnosis, but it should be interpreted with due regard to the clinical setting and radiological features, and with a knowledge of the wide morphological variations seen in mesothelioma. This review identifies some of these problems and addresses the uses and limitations of immunohistochemistry in different situations. It includes a discussion of some of the less common variants of mesothelioma and other pleural-based tumours that enter into the differential diagnosis.