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

BAP1 immunohistochemistry and p16 FISH results in combination provide higher confidence in malignant pleural mesothelioma diagnosis: ROC analysis of the two tests

Differentiation of malignant pleural mesothelioma (MPM) from benign mesothelial proliferation remains problematic. Loss of nuclear staining of BRCA1-associated protein 1 (BAP1; detected using immunohistochemistry (IHC)) and homozygous deletion (HD) of p16 (detected using fluorescence in situ hybridization (FISH)) are useful for differentiation of MPM from reactive mesothelial hyperplasia (RMH), but the correlation between BAP1 expression loss and p16 HD has not been fully described. We performed BAP1 IHC and p16-specific FISH for 40 MPM and 20 RMH cases, and measured proportions of cells showing BAP1 expression and p16 HD for each case. The diagnostic accuracy for MPM and the cut-off values of the two methods were assessed using receiver operating characteristic (ROC) analysis. BAP1 expression loss, p16 HD and coexistence of both were present in 27 (67.5 %), 27 (67.5 %) and 17 (42.5 %) MPM cases, respectively. Three MPM cases (7.5 %) and all 20 RMH cases had neither BAP1 loss nor p16 HD. There was no correlation between the results of the two methods. Their combination showed higher sensitivity (92.5 %, 37/40) and estimated probability than BAP1 IHC and p16-specific FISH used alone. BAP1 IHC and p16-specific FISH have independent diagnostic value, and have increased reliability when used in combination, for MPM diagnosis.

Use of p16 FISH for differential diagnosis of mesothelioma in smear preparations

Because most of malignant pleural mesothelioma (MPM) patients first present with pleural effusion, detection of mesothelioma cells on effusion smears is critical for early diagnosis. Recently, accumulating evidence indicating that the cytological diagnosis of MPM supported by ancillary techniques is as reliable as that based on histopathology has led to new guidelines for the cytopathologic diagnosis of MPM. Based on the guidelines, a combination of cytomorphological criteria and verification by ancillary techniques is required for the cytologic diagnosis of MPM. Detection of p16 homozygous deletion by fluorescence in situ hybridization (FISH) is the most reliable ancillary technique for differentiating MPM from reactive mesothelial cells (RMC) because of its relatively high sensitivity and extremely high specificity. We showed that the p16 deletion status of MPM cells in pleural effusions reflected that of the underlying invasive MPM tissues, indicating the usefulness of p16 FISH in effusion smear cytology for MPM diagnosis. Thus, for differentiating MPM from RMC, we propose to perform p16 FISH as often as possible. A positive p16 homozygous deletion supports the diagnosis of MPM. However, a negative result does not rule out the possibility of MPM. In such cases, a morphological assessment is critical. Therefore, we analyzed the morphological characteristics of p16 deletion-positive mesothelioma cells using a combination of virtual microscopy and p16 FISH, and identified three morphological characteristics useful for the differentiation, including cell-in-cell engulfment with or without hump formation, multinucleate cells, and larger berry-like cell aggregates. Diagn. Cytopathol. 2016;44:774-780. © 2016 Wiley Periodicals, Inc.

Pre-analytical issues in effusion cytology

Effusions or body cavity fluids are amongst the most commonly submitted samples to the cytology laboratory. Knowledge of proper collection, storage, preservation and processing techniques is essential to ensure proper handling and successful analysis of the sample. This article describes how the effusions should be collected and proper conditions for submission. The different processing techniques to extract the cellular material and prepare slides satisfactory for microscopic evaluation are described such as direct smears, cytospins, liquid based preparations and cell blocks. The article further elaborates on handling the specimens for additional ancillary testing such as immunostaining and molecular tests, including predictive ones, as well as future research approaches.

Deletion status of p16 in effusion smear preparation correlates with that of underlying malignant pleural mesothelioma tissue

Differentiating malignant pleural mesothelioma (MPM) cells morphologically from reactive mesothelial hyperplasia cells is problematic. Homozygous deletion (HD) of p16 (CDKN2A), detected by FISH, is a good marker of malignancy and is useful to differentiate between these cells. However, the correlation between the p16 status of effusion smears and that of the underlying MPM tissues has not been investigated. We used p16‐specific FISH to investigate 20 cases of MPM from which both effusion cytologic smears and histologic specimens were available. In five cases, histologic specimens included both an invasive component and surface mesothelial proliferation. In 14 cases (70%), MPM cells in both tissue sections and effusion smears were p16 HD‐positive. Conversely, MPM cells in the remaining six tumors (30%) were p16 HD‐negative in both tissue sections and effusion smears. For all five MPM cases with surface mesothelial proliferations and invasive components, the effusion smears, surface mesothelial proliferations, and invasive MPM components all displayed p16 deletion. Moreover, the extent to which p16 was deleted in smears highly correlated with the extent of p16 deletion in tissues. The p16 deletion percentages were also similar among smears, tissue surface proliferations, and invasive components. In cases with clinical and radiologic evidence of a diffuse pleural tumor, detection of p16 deletion in cytologic smear samples may permit MPM diagnosis without additional tissue examination. However, the absence of p16 deletion in cytologic smear samples does not preclude MPM.

Malignant mesothelioma as an oxidative stress-induced cancer: An update

Malignant mesothelioma (MM) is a relatively rare cancer that occurs almost exclusively following respiratory exposure to asbestos in humans. Its pathogenesis is closely associated with iron overload and oxidative stress in mesothelial cells. On fiber exposure, mesothelial cells accumulate fibers simultaneously with iron, which either performs physical scissor function or catalyzes free radical generation, leading to oxidative DNA damage such as strand breaks and base modifications, followed by activation of intracellular signaling pathways. Chrysotile, per se without iron, causes massive hemolysis and further adsorbs hemoglobin. Exposure to indigestible foreign materials also induces chronic inflammation, involving consistent generation of free radicals and subsequent activation of NALP3 inflammasomes in macrophages. All of these contribute to mesothelial carcinogenesis. Genomic alterations most frequently involve homozygous deletion of INK4A/4B, and other pathways such as Hippo and TGF-β pathways are also affected in MM. Recently, analyses of familial MM sorted out BAP1 as a novel responsible tumor suppressor gene, whose function is not fully elucidated. Five-year survival of mesothelioma is still ~8%, and this cancer is increasing worldwide. Connective tissue growth factor, a secretory protein creating a vicious cycle mediated by β-catenin, has been recognized as a hopeful target for therapy, especially in sarcomatoid subtype. Recent research outcomes related to microRNAs and cancer stem cells also offer additional novel targets for the treatment of MM. Iron reduction as chemoprevention of mesothelioma is helpful at least in an animal preclinical study. Integrated approaches to fiber-induced oxidative stress would be necessary to overcome this currently fatal disease.

p16/CDKN2A FISH in Differentiation of Diffuse Malignant Peritoneal Mesothelioma From Mesothelial Hyperplasia and Epithelial Ovarian Cancer

OBJECTIVES

It can be difficult to differentiate diffuse malignant peritoneal mesothelioma (DMPM) from reactive mesothelial hyperplasia (RMH) or peritoneal dissemination of gynecologic malignancies, such as epithelial ovarian cancer (EOC), which cause a large amount of ascites. Detection of the homozygous deletion of p16/CDKN2A (p16) by fluorescence in situ hybridization (FISH) is an effective adjunct in the diagnosis of malignant pleural mesothelioma. The aim of this study was to investigate the ability of the p16 FISH assay to differentiate DMPM from RMH and EOC.

METHODS

p16 FISH was performed in 28 DMPMs (successful in 19), 30 RMHs, and 40 EOC cases. The cutoff values of p16 FISH were more than 10% for homozygous deletion and more than 40% for heterozygous deletion.

RESULTS

According to the above criteria, nine (47.4%) of 19 successful DMPM cases were homozygous deletion positive, and three (15.8%) of 19 were heterozygous deletion positive, whereas all RMH cases were negative for the p16 deletion. In all four major histologic subtypes of EOC, neither p16 homozygous nor heterozygous deletions were detected. To differentiate DMPM from RMH or EOC, the sensitivity of the p16 homozygous deletion was 32% (9/28), and the specificity was 100%.

CONCLUSIONS

Our study suggests that p16 FISH analysis is useful in differentiating DMPM from RMH and EOC when homozygous deletion is detected.

Personalized oncogenomics: clinical experience with malignant peritoneal mesothelioma using whole genome sequencing

Peritoneal mesothelioma is a rare and sometimes lethal malignancy that presents a clinical challenge for both diagnosis and management. Recent studies have led to a better understanding of the molecular biology of peritoneal mesothelioma. Translation of the emerging data into better treatments and outcome is needed. From two patients with peritoneal mesothelioma, we derived whole genome sequences, RNA expression profiles, and targeted deep sequencing data. Molecular data were made available for translation into a clinical treatment plan. Treatment responses and outcomes were later examined in the context of molecular findings. Molecular studies presented here provide the first reported whole genome sequences of peritoneal mesothelioma. Mutations in known mesothelioma-related genes NF2, CDKN2A, LATS2, amongst others, were identified. Activation of MET-related signaling pathways was demonstrated in both cases. A hypermutated phenotype was observed in one case (434 vs. 18 single nucleotide variants) and was associated with a favourable outcome despite sarcomatoid histology and multifocal disease. This study represents the first report of whole genome analyses of peritoneal mesothelioma, a key step in the understanding and treatment of this disease.

Practical utility of insulin-like growth factor II mRNA-binding protein 3, glucose transporter 1, and epithelial membrane antigen for distinguishing malignant mesotheliomas from benign mesothelial proliferations

The differentiation of malignant mesotheliomas and benign mesothelial proliferations is crucial in determining patient care and prognosis. But, this distinction can be extremely difficult, particularly in small biopsies. Recently, insulin-like growth factor II mRNA-binding protein 3 (IMP3) and glucose transporter 1 (GLUT-1) have been reported as specific and sensitive markers in the distinction of mesotheliomas from benign mesothelial proliferations. The purpose of this study is to evaluate the utility of IMP3, GLUT-1, and epithelial membrane antigen (EMA) immunohistochemistry for distinguishing mesotheliomas from benign mesothelial proliferations. Immunoexpression of IMP3, GLUT-1, and EMA was evaluated in 88 malignant mesotheliomas, 35 adenomatoid tumors, and 20 benign lung tissues with reactive mesothelial cells. The sensitivity for IMP3, GLUT-1, and EMA was 37%, 21%, and 41%, respectively. The specificity for IMP3, GLUT-1, and EMA was 100%. When IMP3, GLUT1, and EMA combined, the sensitivity was 66% for IMP3/EMA staining, 53% for GLUT-1/EMA staining, and 45% for IMP3/GLUT-1. Use of IMP3 and EMA together is more helpful to distinguish malignant mesotheliomas from benign mesothelial proliferations than the use of IMP3 or EMA alone.

The biomolecular era for thoracic surgeons: the example of the ESTS Biology Club

Understanding basic mechanisms of lung disease may help to move forward the management of our patients. Molecular biology has affected our diagnostic and therapeutic pathways in the direction of personalized medicine not only for thoracic malignancies. Accordingly, thoracic surgeons are becoming increasingly aware that specific knowledge of genetic and epigenetic alterations may influence their clinical behavior-from the ward to the operating room (OR). In this continuously evolving scenario, surgical societies have perceived the increasing relevance of biomolecular medicine in the practice of modern thoracic surgery. More recently, in the spirit of mutual collaboration between sister societies, the European Society of Thoracic Surgeons (ESTS) has adopted the concept of the American Association for Thoracic Surgery (AATS) incorporating one session dedicated to the Biology Club within the Annual Meeting Program. The aim of the ESTS Biology Club is to outline and sponsor the new profile of the surgeon scientist during the only world meeting exclusively focused on general thoracic surgery. The following article will summarize the significance of this and give an update on molecular biology tools for thoracic malignancies.

Morphology of 9p21 homozygous deletion-positive pleural mesothelioma cells analyzed using fluorescence in situ hybridization and virtual microscope system in effusion cytology

BACKGROUND

In malignant pleural mesothelioma (MPM), most patients first present with pleural effusion; thus, cytologic analysis is the primary diagnostic approach. However, the cytologic distinction between MPM and reactive mesothelial cells (RMCs) in effusions can be extremely difficult due to the lack of both well-established immunocytochemical markers and definite cytological criteria for MPM. Moreover, the existence of both MPM cells and RMCs in effusions from the same patient makes the differentiation even more challenging. Homozygous deletion of the 9p21 locus, the site of the cyclin-dependent kinase inhibitor 2A/p16 (CDKN2A/p16) gene, frequently occurs in MPM but has never been reported in RMCs. The aim of this study was to define the cytomorphological characteristics of MPM cells, identified by the presence of 9p21 homozygous deletion by fluorescence in situ hybridization (FISH).

METHODS

For this purpose, cells on smear preparations were recorded using a virtual microscope system and were subjected to FISH analysis. Thereafter, 9p21 homozygous deletion-positive cells were identified in the recorded virtual slides, followed by analysis of their morphological characteristics.

RESULTS

Mesothelioma cells positive for the 9p21 homozygous deletion exhibited significantly more frequent cell-in-cell engulfment, multinucleation (more than 2 nuclei), and larger multicellular clusters composed of more than 10 cells than did 9p21 deletion-negative RMCs. Possible cutoff values are also proposed for these morphological markers to differentiate MPM cells from RMCs.

CONCLUSIONS

These morphological differences and cutoff values are useful for cytological differentiation of mesothelioma cells from RMCs. In addition, the novel technique of a combination of virtual microscopy and FISH is introduced for tumor morphological analysis.

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.

Guidelines for pathologic diagnosis of malignant mesothelioma: 2012 update of the consensus statement from the International Mesothelioma Interest Group

CONTEXT

Malignant mesothelioma (MM) is an uncommon tumor that can be difficult to diagnose.

OBJECTIVE

To provide updated practical guidelines for the pathologic diagnosis of MM.

DATA SOURCES

Pathologists involved in the International Mesothelioma Interest Group and others with an interest in the field contributed to this update. Reference material includes peer-reviewed publications and textbooks.

CONCLUSIONS

There was consensus opinion regarding (1) distinction of benign from malignant mesothelial proliferations (both epithelioid and spindle cell lesions), (2) cytologic diagnosis of MM, (3) key histologic features of pleural and peritoneal MM, (4) use of histochemical and immunohistochemical stains in the diagnosis and differential diagnosis of MM, (5) differentiation of epithelioid MM from various carcinomas (lung, breast, ovarian, and colonic adenocarcinomas, and squamous cell and renal cell carcinomas), (6) diagnosis of sarcomatoid mesothelioma, (7) use of molecular markers in the diagnosis of MM, (8) electron microscopy in the diagnosis of MM, and (9) some caveats and pitfalls in the diagnosis of MM. Immunohistochemical panels are integral to the diagnosis of MM, but the exact makeup of panels used is dependent on the differential diagnosis and on the antibodies available in a given laboratory. Immunohistochemical panels should contain both positive and negative markers. It is recommended that immunohistochemical markers have either sensitivity or specificity greater than 80% for the lesions in question. Interpretation of positivity generally should take into account the localization of the stain (eg, nuclear versus cytoplasmic) and the percentage of cells staining (>10% is suggested for cytoplasmic membranous markers). These guidelines are meant to be a practical reference for the pathologist.

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.

Molecular changes in mesothelioma with an impact on prognosis and treatment

CONTEXT

In recent decades, research on malignant pleural mesothelioma (MPM) has been developed to improve patients' outcomes by increasing the level of confidence in MPM diagnosis and prognosis.

OBJECTIVE

To summarize data on genetic and epigenetic abnormalities in MPM that may be of interest for a better management of patients with MPM.

DATA SOURCES

Data were obtained from scientific publications on genetic and epigenetic abnormalities in MPM by studying gene mutations, DNA methylation, and gene and microRNA expression profiling.

CONCLUSIONS

Molecular changes in MPM consist in altered expression and in activation or inactivation of critical genes in oncogenesis, especially tumor suppressor genes at the INK4 and NF2 loci. Activation of membrane receptor tyrosine kinases and deregulation of signaling pathways related to differentiation, survival, proliferation, apoptosis, cell cycle control, metabolism, migration, and invasion have been demonstrated. Alterations that could be targeted at a global level (methylation) have been recently reported. Experimental research has succeeded especially in abolishing proliferation and triggering apoptosis in MPM cells. So far, targeted clinical approaches focusing on receptor tyrosine kinases have had limited success. Molecular analyses of series of MPM cases have shown that defined alterations are present in MPM subsets, consistent with interindividual variations of molecular alterations, and suggesting that identification of patient subgroups will be essential to develop more specific therapies.

The diagnostic value of immunohistochemically detected methylthioadenosine phosphorylase deficiency in malignant pleural mesotheliomas

AIMS

  Malignant pleural mesothelioma (MPM) often causes diagnostic difficulties for pathologists. We assessed whether loss of methylthioadenosine phosphorylase (MTAP), a key enzyme in the intracellular recycling of adenosine triphosphate (ATP) often deleted in MPM, could be detected with immunohistochemistry (IHC) and used as a diagnostic marker for MPM.

METHODS AND RESULTS

  We used IHC to detect MTAP in a cohort of 99 MPMs and 39 reactive mesothelial proliferations (RP) (reactive mesothelial hyperplasia n = 33, reactive pleural fibrosis n = 6). MTAP staining was assessed by an H score. The median H score of the RP cohort was set as a reference point. Cases with H scores below this reference point were considered to have decreased MTAP expression. We found that 64 of 99 (65%) of the investigated MPMs had decreased MTAP expression, while this was only true for nine of 39 (23%) of the RPs (P = 0.001). We further evaluated MTAP expression in a cohort of coagulated pleural effusions from 14 patients with MPM and 20 patients with RP by using a double-staining technique with Wilms tumour 1 (WT1) as a mesothelial marker. In these samples, decreased MTAP expression diagnosed MPM with a sensitivity of 71% and a specificity of 90%.

CONCLUSIONS

  Decreased MTAP expression could potentially be useful in combination with other markers in the diagnosis of MPM.

YAP induces malignant mesothelioma cell proliferation by upregulating transcription of cell cycle-promoting genes

Malignant mesothelioma (MM) shows frequent inactivation of the neurofibromatosis type 2 (NF2) -tumor-suppressor gene. Recent studies have documented that the Hippo signaling pathway, a downstream cascade of Merlin (a product of NF2), has a key role in organ size control and carcinogenesis by regulating cell proliferation and apoptosis. We previously reported that MMs show overexpression of Yes-associated protein (YAP) transcriptional coactivator, the main downstream effector of the Hippo signaling pathway, which results from the inactivation of NF2, LATS2 and/or SAV1 genes (the latter two encoding core components of the mammalian Hippo pathway) or amplification of YAP itself. However, the detailed roles of YAP remain unclear, especially the target genes of YAP that enhance MM cell growth and survival. Here, we demonstrated that YAP-knockdown inhibited cell motility, invasion and anchorage-independent growth as well as cell proliferation of MM cells in vitro. We analyzed genes commonly regulated by YAP in three MM cell lines with constitutive YAP-activation, and found that the major subsets of YAP-upregulating genes encode cell cycle regulators. Among them, YAP directly induced the transcription of CCND1 and FOXM1, in cooperation with TEAD transcription factor. We also found that knockdown of CCND1 and FOXM1 suppressed MM cell proliferation, although the inhibitory effects were less evident than those of YAP knockdown. These results indicate that constitutive YAP activation in MM cells promotes cell cycle progression giving more aggressive phenotypes to MM cells.

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.

Factors that impact susceptibility to fiber-induced health effects

Asbestos and related fibers are associated with a number of adverse health effects, including malignant mesothelioma (MM), an aggressive cancer that generally develops in the surface serosal cells of the pleural, pericardial, and peritoneal cavities. Although approximately 80% of individuals with MM are exposed to asbestos, fewer than 5% of asbestos workers develop MM. In addition to asbestos, other mineralogical, environmental, genetic, and possibly viral factors might contribute to MM susceptibility. Given this complex etiology of MM, understanding susceptibility to MM needs to be a priority for investigators in order to reduce exposure of those most at risk to known environmental carcinogens. In this review, the current body of literature related to fiber-associated disease susceptibility including age, sex, nutrition, genetics, asbestos, and other mineral exposure is addressed with a focus on MM, and critical areas for further study are recommended.

Lymphohistiocytoid mesothelioma of the pleura

Lymphohistiocytoid mesothelioma (LHM), reported to be a rare variant of sarcomatoid mesothelioma, is challenging to differentiate from non-Hodgkin's lymphoma due to marked lymphocytic infiltration. To aid accurate recognition of LHM, we examined immunohistochemical, in situ hybridization (ISH) of Epstein-Barr virus RNA (EBER-1) mRNA, fluorescence ISH (FISH) for homozygous deletion of 9p21, and asbestos analysis in four cases (three men and 1 woman). Three patients died, while Case 4 was still alive 19 months after extrapleural pneumonectomy. Histologically, these cases were characterized by heavy lymphocytic infiltration. All neoplastic cells were positive for calretinin, AE1/AE3, and epithelial membrane antigen, but negative for CEA. EBER1 factor was negative. FISH analysis demonstrated homozygous deletion of the 9p21 locus in three of the four cases. In Case 1: (i) autopsy findings showed mesothelioma primarily located in the right parietal pleura, but metastasized into the left lung and abdominal organs; (ii) the histological findings at autopsy indicated sarcomatoid mesothelioma; and (iii) we found asbestos bodies and fibers in extracts from lung tissue (Cases 1 & 4) using digestion with bleaching fluid. LHM, an infrequent variant of sarcomatoid mesothelioma, displayed homozygous deletion of the 9p21 locus (three of four cases), and has a relatively favorable prognosis for the sarcomatoid type.

CDKN2A and MTAP deletions in peritoneal mesotheliomas are correlated with loss of p16 protein expression and poor survival

Homozygous deletion of CDKN2A (p16) is one of the most common genetic alterations in pleural mesotheliomas, occurring in up to 74% of cases. MTAP resides in the same gene cluster of the 9p21 region and is co-deleted in the majority of CDKN2A deleted cases. This study examines the genetic alterations in peritoneal mesotheliomas, which may have a different pathogenesis than their pleural counterparts. Twenty-six cases of peritoneal mesotheliomas in a triplicate tissue microarray were studied. Dual-color fluorescence in situ hybridization was performed with CDKN2A and MTAP locus-specific probes. Nine of 26 (35%) peritoneal mesotheliomas had homozygous deletion of CDKN2A; MTAP was co-deleted in every case. All cases with CDKN2A deletions had loss of p16 protein expression; five cases had loss of p16 protein without evidence of CDKN2A deletions. All patients with CDKN2A deletions were men (P, NS) and were significantly older (mean, 63 years) than the patients with no deletions (mean, 52 years) (P=0.033, t-test). An association with asbestos exposure could not be proved in this study. Similar to pleural mesotheliomas, patients with CDKN2A deletions and loss of p16 protein expression had worse overall and disease-specific survival (P=0.010 and 0.006, respectively; Kaplan-Meier log rank). Detection of CDKN2A-MTAP co-deletion in peritoneal mesotheliomas, coupled with a p16 immunohistochemical stain as an inexpensive screening tool, can help identify those patients who may have an unfavorable outcome after aggressive cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy and those who may respond to targeted therapy of the MTAP pathway.

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.

Fluorescence in situ hybridization in the definitive diagnosis of malignant mesothelioma in effusion cytology

BACKGROUND

Distinction of malignant mesothelioma (MM) from reactive mesothelial cells (RM) in effusions is notoriously difficult. The aim of our study was to test chromosomal aberrations detected by fluorescence in situ hybridization (FISH) in the diagnosis of MM in effusion cytology and to explore the potential role of p16, p14, and p15 gene methylation as an alternative mechanism of tumor suppressor gene inactivation.

METHODS

Fifty-two effusions of biopsy-proven MM and 28 benign effusions were retrospectively analyzed by multitarget FISH assay for aberrations of chromosomes 3, 7, 17, and 9p21. In case of a negative result, the corresponding MM biopsy specimen was analyzed. Methylation-specific polymerase chain reaction (MSP) for p16, p14, and p15 was performed on FISH-negative MM biopsy specimens.

RESULTS

Seventy-nine percent of effusions with biopsy-proven MM had chromosomal aberrations, with loss of 9p21 as the most common finding. All benign effusions were FISH negative. Sensitivity, specificity, and positive and negative predictive values for detection of MM by FISH were 79%, 100%, 100%, and 72%, respectively. Six of nine FISH-negative effusions with biopsy-proven MM were also FISH negative in the MM biopsy specimens. Four of five FISH-negative biopsy specimens showed promoter methylation in p16 and p14 as compared with one of 12 benign controls.

CONCLUSIONS

FISH is a sensitive and highly specific method for the definitive diagnosis of MM in effusion cytology. In the subset of FISH-negative MM, tumor suppressor genes on the chromosomal region 9p21 are often inactivated by promoter methylation.

Prognostic significance of p16/cdkn2a loss in pleural malignant mesotheliomas

Homozygous deletion of p16/CDKN2A is the most common genetic abnormality in malignant mesotheliomas. The aim of this study was to determine prognostic significance of p16/CDKN2A loss in malignant pleural mesotheliomas (MPM) as defined by immunohistochemistry and fluorescence in situ hybridization (FISH). High-density tissue microarrays were constructed from archival formalin-fixed paraffin-embedded samples of 48 MPM. Long survival (LS) was defined as survival greater than 3 years from the time of diagnosis, and short survival was defined as less than 3 years from the time of diagnosis. Both loss of p16 protein expression by immunohistochemistry and homozygous deletion of p16 by FISH were associated with adverse prognosis. Female gender, positive p16 immunoexpression, and lack of p16/CDKN2A deletion significantly predicted the survival for the LS group. Statistical analysis showed a very strong correlation of immunohistochemistry and FISH data. Cases positive for p16 immunoexpression and negative for 9p21 deletion showed the best survival time. Our study is the first to demonstrate decreased frequency of homozygous deletion of 9p21 and loss of p16 immunoreactivity in pleural mesotheliomas from patients with long-term survival of greater than 3 years in contrast to patients with rapidly fatal mesotheliomas. A possible implementation of these tests into preoperative prognostication of MPM and therapeutic decisions should be considered.

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.

Frequent p16 inactivation by homozygous deletion or methylation is associated with a poor prognosis in Japanese patients with pleural mesothelioma

This study examined the p16 expression status and the P16 gene deletion and methylation status in specimens from Japanese patients with malignant pleural mesothelioma (MPM). Immunohistochemical staining for p16 protein and fluorescence in situ hybridization for the P16 gene were performed using specimens from 30 Japanese patients with primary MPM. The methylation status of the P16 gene was examined in 13 patients whose frozen tumor specimens were available using a methylation-specific PCR assay. Among the 30 patients, the loss of p16 protein expression was observed in 24 patients (80.0%). Twenty-one patients had homozygous deletions, and 9 patients retained the P16 gene. None of the patients with P16 homozygous deletions exhibited p16-positive expression, and 3 patients who retained the P16 gene did not exhibit p16-positive expression. Aberrant P16 methylation was present in two patients with an intact P16 gene but without p16 expression. These results suggest that either a homozygous deletion or methylation is responsible for P16 inactivation. Regarding the prognosis, patients with p16-negative expression had a significantly shorter survival time than those with p16-positive expression (P=0.040). Our study showed that P16 inactivation by homozygous deletions or methylation is a frequent event in Japanese patients with MPMs, relating to poor prognosis. Homozygous deletion is the major cause of P16 inactivation, but methylation also lead to the inactivation of P16 when the P16 alleles are retained.

Update on the molecular biology of malignant mesothelioma

Malignant mesothelioma (MM) is a highly aggressive tumor with a very poor prognosis. The disease is largely unresponsive to conventional chemotherapy or radiotherapy, and most patients die within 10-17 months of the first symptoms. Novel, more effective therapeutic strategies are needed for this inexorably fatal disease. Improvement in our understanding of the molecular biology of MM has identified promising new candidates for targeted treatments. In this review the key molecular signaling pathways, including vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), Wnt, and the cell cycle control genes p53, pRb, and bcl-2 that appear to play an important role in the pathogenesis of MM are explored.

Expression of Cancer-Associated Molecules in Malignant Mesothelioma

Malignant mesothelioma (MM) is a malignant tumor derived from mesothelial cells, native cells of the body cavities. Exposure to asbestos is the most strongly established etiologic factor, predominantly for the most common disease form, pleural mesothelioma. The pathogenesis of MM involves the accumulation of extensive cytogenetic changes, as well as cancer-related phenotypic alterations that facilitate tumor cell survival, invasion and metastasis. This review presents current knowledge regarding the biological characteristics of this disease that are linked to the so-called hallmarks of cancer. In addition, data suggesting that the anatomic site (solid tumor vs. effusion) affects the expression of metastasis-associated and regulatory molecules in MM are presented. Finally, recent work in which high-throughput methodology has been applied to MM research is reviewed. The data obtained in the reviewed research may aid in defining new prognostic markers and therapeutic targets for this aggressive disease in the future.

Gene expression profiling and gene copy-number changes in malignant mesothelioma cell lines

Malignant mesothelioma (MM) is an asbestos-induced tumor that acquires aneuploid DNA content during the tumorigenic process. We used instable MM cell lines as an in vitro model to study the impact of DNA copy-number changes on gene expression profiling, in the course of their chromosomal redistribution process. Two MM cell lines, PMR-MM2 (early passages of in vitro culture) and PMR-MM7 (both early and late passages of in vitro culture), were cytogenetically characterized. Genomic gains and losses were precisely defined using microarray-based comparative genomic hybridization (array-CGH), and minimal overlapping analysis led to the identification of the common unbalanced genomic regions. Using the U133Plus 2.0 Affymetrix gene chip array, we analyzed PMR-MM7 early and late passages for genome-wide gene expression, and correlated the differentially expressed genes with copy-number changes. The presence of a high number of genetic imbalances occurring from early to late culture steps reflected the tendency of MM cells toward genomic instability. The selection of specific chromosomal abnormalities observed during subsequent cultures demonstrated the spontaneous evolution of the cancer cells in an in vitro environment. MM cell lines were characterized by copy-number changes associated with the TP53 apoptotic pathway already present at the first steps of in vitro culture. Prolonged culture led to acquisition of additional chromosomal copy-number changes associated with dysregulation of genes involved in cell adhesion, regulation of mitotic cell cycle, signal transduction, carbohydrate metabolism, motor activity, glycosaminoglycan biosynthesis, protein binding activity, lipid transport, ATP synthesis, and methyltransferase activity.

Cytogenetic and molecular genetic changes in malignant mesothelioma

Malignant mesothelioma (MM) results from the accumulation of a number of acquired genetic events, especially deletions, which lead to the inactivation of multiple onco-suppressor genes in a multistep cascade mechanism. Past asbestos exposure represents the major risk factor for MM, and the link between asbestos fibers and MM has been largely proved by several epidemiologic and experimental studies. Asbestos fibers induce DNA and chromosomal damage. Most MM cases have shown multiple chromosomal abnormalities. Chromosomal losses are more common than gains. The most common cytogenetic abnormality in MM is a deletion in 9p21, the locus of CDKN2A, a tumor suppressor gene (TSG). The deletion of CDKN2A is a negative prognostic factor in MM. Loss of TSG CDKN2A/p14(ARF) is also common in MM and mutations in NF2 occur in approximately half of the cases. Despite the ban on asbestos use in Western countries, the incidence of MM is increasing, and asbestos is still used in developing countries. This epidemiologic situation calls for further research. Ongoing studies are already applying high-throughput genomic profiling methods in MM. Genetic alterations observed in MM may be useful in differential diagnosis between lung cancer and MM, as diagnostic markers or therapeutic targets, and as indicators of premalignancy for primary prevention and health surveillance.

A Molecular Diagnostic Test for Distinguishing Lung Adenocarcinoma from Malignant Mesothelioma Using Cells Collected from Pleural Effusions

PURPOSE

Patients with malignant mesothelioma or adenocarcinoma of the lung often present with respiratory complications associated with a malignant pleural effusion. Distinguishing between these malignancies is frequently problematic, as many of the clinical, cytologic, and histologic features of the diseases overlap. Following cytologic analysis of pleural effusions, subsequent confirmatory tissue biopsies involve increased patient morbidity and expense. We have therefore designed a gene expression-based test to classify the primary tumor causing a malignant pleural effusion, using cells collected from the effusion itself.

EXPERIMENTAL DESIGN

We have used microarray data for 190 lung adenocarcinomas and 33 malignant mesotheliomas to identify genes differentially expressed between the two diseases. Genes expressed in normal mesothelial cells were removed, allowing the development of a PCR-based test to measure the expression of genes that discriminate between mesothelioma and lung adenocarcinoma from cytology specimens.

RESULTS

Applying an real-time PCR-based assay involving 17 genes to 13 independent samples from biopsy-proven malignant mesothelioma and lung adenocarcinomas resulted in the correct identification of all samples.

CONCLUSIONS

We have developed a test that is able to distinguish between lung adenocarcinoma and mesothelioma in cells collected from pleural effusions.