Updates on the cytogenetics and molecular genetics of bone and soft tissue tumors. Mesothelioma

Pathology of Malignant Pleural Mesothelioma

Despite multiple diagnostic toolkits, the diagnosis of diffuse malignant pleural mesothelioma relies primarily on proper histologic assessment. The definitive diagnosis of diffuse malignant pleural mesothelioma is based on the pathologic assessment of tumor tissue, which can be obtained from core biopsy sampling, pleurectomy, or other more extensive resections, such as extrapleural pneumonectomy. Given its rarity and overlapping microscopic features with other conditions, the histologic diagnosis of diffuse malignant pleural mesothelioma is challenging. This review discusses the pathologic features and the differential diagnosis of diffuse malignant pleural mesothelioma, including select diagnostic pitfalls.

Molecular characterization of localized pleural mesothelioma

Localized pleural mesothelioma is a rare solitary circumscribed pleural tumor that is microscopically similar to diffuse malignant pleural mesothelioma. However, the molecular characteristics and nosologic relationship with its diffuse counterpart remain unknown. In a consecutive cohort of 1110 patients with pleural mesotheliomas diagnosed in 2005-2018, we identified six (0.5%) patients diagnosed with localized pleural mesotheliomas. We gathered clinical history, evaluated the histopathology, and in select cases performed karyotypic analysis and targeted next-generation sequencing. The cohort included three women and three men (median age 63; range 28-76), often presenting incidentally during radiologic evaluation for unrelated conditions. Neoadjuvant chemotherapy was administered in two patients. All tumors (median size 5.0 cm; range 2.7-13.5 cm) demonstrated gross circumscription (with microscopic invasion into lung, soft tissue, and/or rib in four cases), mesothelioma histology (four biphasic and two epithelioid types), and mesothelial immunophenotype. Of four patients with at least 6-month follow-up, three were alive (up to 8.9 years). Genomic characterization identified several subgroups: (1) BAP1 mutations with deletions of CDKN2A and NF2 in two tumors; (2) TRAF7 mutations in two tumors, including one harboring trisomies of chromosomes 3, 5, 7, and X; and (3) genomic near-haploidization, characterized by extensive loss of heterozygosity sparing chromosomes 5 and 7. Localized pleural mesotheliomas appear genetically heterogeneous and include BAP1-mutated, TRAF7-mutated, and near-haploid subgroups. While the BAP1-mutated subgroup is similar to diffuse malignant pleural mesotheliomas, the TRAF7-mutated subgroup overlaps genetically with adenomatoid tumors and well-differentiated papillary mesotheliomas, in which recurrent TRAF7 mutations have been described. Genomic near-haploidization, identified recently in a subset of diffuse malignant pleural mesotheliomas, suggests a novel mechanism in the pathogenesis of both localized pleural mesothelioma and diffuse malignant pleural mesothelioma. Our findings describe distinctive genetic features of localized pleural mesothelioma, with both similarities to and differences from diffuse malignant pleural mesothelioma.

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.

Comparative genetic analysis of a rare synchronous collision tumor composed of malignant pleural mesothelioma and primary pulmonary adenocarcinoma

Background

Although asbestos acts as a potent carcinogen in pleural mesothelial and pulmonary epithelial cells, it still remains unclear whether asbestos causes specific and characteristic gene alterations in these different kinds of target cells, because direct comparison in an identical patient is not feasible. We experienced a rare synchronous collision tumor composed of malignant pleural mesothelioma (MPM) and primary pulmonary adenocarcinoma (PAC) in a 77-year-old man with a history of long-term smoking and asbestos exposure, and compared the DNA copy number alteration (CNA) and somatic mutation in these two independent tumors.

Methods

Formalin-fixed paraffin-embedded (FFPE) tissues of MPM and PAC lesions from the surgically resected specimen were used. Each of these MPM and PAC lesions exhibited a typical histology and immunophenotype. CNA analysis using SNP array was performed using the Illumina Human Omni Express-12_FFPE (Illumina, San Diego, CA, USA) with DNA extracts from each lesion. Somatic mutation analysis using next-generation sequencing was performed using the TruSeq Amplicon Cancer Panel (Illumina).

Results

The CNA analysis demonstrated a marked difference in the frequency of gain and loss between MPM and PAC. In PAC, copy number (CN) gain was detected more frequently and widely than CN loss, whereas in MPM there was no such obvious difference. PAC did not harbor CNAs that have been identified in asbestos-associated lung cancer, but did harbor some of the CNAs associated with smoking. MPM exhibited CN loss at 9p21.2-3, which is the most common genetic alteration in mesothelioma.

Conclusion

In this particular case, asbestos exposure may not have played a primary role in PAC carcinogenesis, but cigarette smoking may have contributed more to the occurrence of CN gains in PAC. This comparative genetic analysis of two different lesions with same amount of asbestos exposure and cigarette smoke exposure has provided information on differences in the cancer genome related to carcinogenesis.

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.

Comparison of genomic abnormality in malignant mesothelioma by the site of origin

AIMS

Malignant mesothelioma (MM) results from the accumulation of a number of acquired genetic events at the onset. In MM, the most frequent changes are losses in 9p21, 1p36, 22q12 and 14q32, and gains in 5p, 7p and 8q24 by comparative genomic hybridisation analysis. We have examined various genomic losses and gains in MM and benign mesothelial proliferation by fluorescence in situ hybridisation (FISH) analysis. 9p21 deletion was reported to be less frequent in peritoneal than in pleural MMs. This study analysed various genomic losses and gains in MM by the site of origin using FISH analysis.

MATERIALS AND METHODS

We performed FISH analysis using paraffin-embedded tissues from 54 cases (40 pleural and 14 peritoneal) of MMs and compared the frequency of genomic abnormality by the site of origin.

RESULTS

9p21 deletion was shown in 34 of 40 cases (85%) of pleural MMs, and was less frequent in five of 14 cases (36%) of peritoneal MMs (p<0.001) by FISH analysis. By contrast, 5p15 and 7p12 amplification was more significantly frequent in peritoneal than in pleural MMs. No difference between the two sites of MM in other genes was found.

CONCLUSIONS

9p21 homozygous deletion assessed by FISH has been reported to be useful for differentiating MM from reactive mesothelial proliferation, but it should be noted that 9p21 deletion was less frequent in peritoneal MM. Our study suggests that the pathway of the genetic abnormality might vary between pleural and peritoneal MM.

Claudin-4 immunohistochemistry is highly effective in distinguishing adenocarcinoma from malignant mesothelioma in effusion cytology

BACKGROUND

Adenocarcinoma can be challenging to distinguish from malignant mesothelioma in effusions, and this distinction often requires ancillary studies and clinical correlation. Immunohistochemistry for claudin-4, a tight-junction-associated protein, has recently been shown to distinguish adenocarcinoma from malignant mesothelioma, mostly in surgical specimens. Our aim was to validate and assess the immunoreactivity profile of claudin-4 in a large series of malignant effusions.

METHODS

We evaluated 159 malignant effusions (84 adenocarcinomas and 75 malignant mesotheliomas). Claudin-4 immunohistochemistry was performed on cell-block paraffin sections and scored for staining intensity, staining pattern (cytoplasmic versus membranous), and percentage of positive tumor cells. Appropriate positive and negative controls were used throughout.

RESULTS

All cases of mesothelioma were negative for claudin-4 (0 of 64). Eighty-three of 84 cases of adenocarcinoma were positive (99%); 1 case of serous carcinoma was negative. Most adenocarcinomas showed strong and diffuse membranous staining (71 of 84; 84%); 12 cases (14%) showed membranous staining of moderate intensity. The overall sensitivity for adenocarcinoma was 99% (83 of 84).

CONCLUSIONS

Claudin-4 immunohistochemistry effectively distinguishes adenocarcinoma from malignant mesothelioma with high sensitivity and specificity in the evaluation of malignant effusions.

Integrated high-resolution array CGH and SKY analysis of homozygous deletions and other genomic alterations present in malignant mesothelioma cell lines

High-resolution oligonucleotide array comparative genomic hybridization (aCGH) and spectral karyotyping (SKY) were applied to a panel of malignant mesothelioma (MMt) cell lines. SKY has not been applied to MMt before, and complete karyotypes are reported based on the integration of SKY and aCGH results. A whole genome search for homozygous deletions (HDs) produced the largest set of recurrent and non-recurrent HDs for MMt (52 recurrent HDs in 10 genomic regions; 36 non-recurrent HDs). For the first time, LINGO2, RBFOX1/A2BP1, RPL29, DUSP7, and CCSER1/FAM190A were found to be homozygously deleted in MMt, and some of these genes could be new tumor suppressor genes for MMt. Integration of SKY and aCGH data allowed reconstruction of chromosomal rearrangements that led to the formation of HDs. Our data imply that only with acquisition of structural and/or numerical karyotypic instability can MMt cells attain a complete loss of tumor suppressor genes located in 9p21.3, which is the most frequently homozygously deleted region. Tetraploidization is a late event in the karyotypic progression of MMt cells, after HDs in the 9p21.3 region have already been acquired.

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.

Deciduoid pleural mesothelioma--a rare entity in a young woman

Deciduoid Mesothelioma is a rare variant of epithelioid mesothelioma; it was initially thought that it only occurred in the peritoneum of young women and had nothing to do with asbestos exposure. However, since these early findings it has also been observed in the pleura and the pericardium, with possible association to asbestos. In general the prognosis is poor compared to epithelioid mesothelioma. 45 cases have been reported in the literature up to now, 22 of these were located in the pleural cavity. The authors describe a case of deciduoid pleural mesothelioma in a 40-year-old-woman who presented with right pleuritic chest pain, with no history of asbestos exposure, treated with chemotherapy followed by surgery and who died postoperatively.

Syntenic relationships between genomic profiles of fiber-induced murine and human malignant mesothelioma

Malignant mesothelioma (MM) is an aggressive tumor with a poor prognosis mainly linked to past asbestos exposure. Murine models of MM based on fiber exposure have been developed to elucidate the mechanism of mesothelioma formation. Genomic alterations in murine MM have now been partially characterized. To gain insight into the pathophysiology of mesothelioma, 16 murine and 35 human mesotheliomas were characterized by array-comparative genomic hybridization and were screened for common genomic alterations. Alteration of the 9p21 human region, often by biallelic deletion, was the most frequent alteration in both species, in agreement with the CDKN2A/CDKN2B locus deletion in human disease and murine models. Other shared aberrations were losses of 1p36.3-p35 and 13q14-q33 and gains of 5p15.3-p13 regions. However, some differences were noted, such as absence of recurrent alterations in mouse regions corresponding to human chromosome 22. Comparison between altered recurrent regions in asbestos-exposed and non-asbestos-exposed patients showed a significant difference in the 14q11.2-q21 region, which was also lost in fiber-induced murine mesothelioma. A correlation was also demonstrated between genomic instability and tumorigenicity of human mesothelioma xenografts in nude mice. Overall, these data show similarities between murine and human disease, and contribute to the understanding of the influence of fibers in the pathogenesis of mesothelioma and validation of the murine model for preclinical testing.

Nearly identical near-haploid karyotype in a peritoneal mesothelioma and a retroperitoneal malignant peripheral nerve sheath tumor

The presence of a near-haploid karyotype is a rare finding in human malignancies, most frequently occurring in acute leukemia. In solid tumors, a near-haploid karyotype has been reported in fewer than 40 cases. We report two nearly identical near-haploid karyotypes from two distinctly different tumor types. The first case is a biphasic malignant mesothelioma from a 53-year-old white woman forming a large retroperitoneal mass. Cytogenetic evaluation revealed a primary hyperdiploid cell population as well as near-haploid and hypertetraploid populations with an overall karyotype of 27,XX,i(5)(p10),+7,add(15)(p11.2),+dic(1;20)(p13;p13)[2]/54,idemx2[90]/101-108,idemx4[19]. The second case is a large pelvic mass from a 48-year-old man. Histologic examination identified a malignant peripheral nerve sheath tumor displaying a karyotype of 26,X,+i(5)(p10),+7,der(15)t(1;15)(q12;p12),+20[5]/52,idemx2[20]. Herein we discuss the potential relationship between these two disparate neoplasms with nearly identical near-haploid karyotypes and present a literature review.

Occupational toxicology of asbestos-related malignancies

INTRODUCTION

Asbestos is banned in most Western countries but related malignancies are still of clinical concern because of their long latencies. This review identifies and addresses some controversial occupational and clinical aspects of asbestos-related malignancies.

METHODS

Papers published in English from 1980 to 2009 were retrieved from PubMed. A total of 307 original articles were identified and 159 were included.

ASSESSMENT OF EXPOSURE

The retrospective assessment of exposure is usually performed by using questionnaires and job exposure matrices and by careful collection of medical history. In this way crucial information about manufacturing processes and specific jobs can be obtained. In addition, fibers and asbestos bodies are counted in lung tissue, broncho-alveolar lavage, and sputum, but different techniques and interlaboratory variability hamper the interpretation of reported measurements. SCREENING FOR MALIGNANCIES: The effectiveness of low-dose chest CT screening in exposed workers is debatable. Several biomarkers have also been considered to screen individuals at risk for lung cancer and mesothelioma but reliable signatures are still missing. ATTRIBUTION OF LUNG CANCER: Exposures correlating with lung cancer are high and in the same range where asbestosis occurs. However, the unresolved question is whether the presence of fibrosis is a requirement for the attribution of lung cancer to asbestos. The etiology of lung cancer is difficult to define in cases of low-level asbestos exposure and concurrent smoking habits. MESOTHELIOMA: The diagnosis of malignant mesothelioma may also be difficult, because of procedures in sampling, fixation, and processing, and uses of immunohistochemical probes.

CONCLUSIONS

Assessment of exposure is crucial and requires accurate medical and occupational histories. Quantitative analysis of asbestos body burden is better performed in digested lung tissues by counting asbestos bodies by light microscopy and/or uncoated fibers by transmission electron microscopy. The benefits of screenings for asbestos-related malignancies are equivocal. The attribution of lung cancer to asbestos exposure is difficult in a clinical setting because of the need to assess asbestos body burden and the fact that virtually all these patients are also tobacco smokers or former smokers. Given the premise that asbestosis is necessary to causally link lung cancer to asbestos, it follows that the assessment of both lung fibrosis and asbestos body burden is necessary.

In vitro and in vivo characterization of highly purified human mesothelioma derived cells

BACKGROUND

Malignant pleural mesothelioma is a rare disease known to be resistant to conventional therapies. A better understanding of mesothelioma biology may provide the rationale for new therapeutic strategies. In this regard, tumor cell lines development has been an important tool to study the biological properties of many tumors. However all the cell lines established so far were grown in medium containing at least 10% serum, and it has been shown that primary cell lines cultured under these conditions lose their ability to differentiate, acquire gene expression profiles that differ from that of tissue specific stem cells or the primary tumor they derive from, and in some cases are neither clonogenic nor tumorigenic. Our work was aimed to establish from fresh human pleural mesothelioma samples cell cultures maintaining tumorigenic properties.

METHODS

The primary cell cultures, obtained from four human pleural mesotheliomas, were expanded in vitro in a low serum proliferation-permissive medium and the expression of different markers as well as the tumorigenicity in immunodeficient mice was evaluated.

RESULTS

The established mesothelioma cell cultures are able to engraft, after pseudo orthotopic intraperitoneal transplantation, in immunodeficient mouse and maintain this ability to after serial transplantation. Our cell cultures were strongly positive for CD46, CD47, CD56 and CD63 and were also strongly positive for some markers never described before in mesothelioma cell lines, including CD55, CD90 and CD99. By real time PCR we found that our cell lines expressed high mRNA levels of typical mesothelioma markers as mesothelin (MSLN) and calretinin (CALB2), and of BMI-1, a stemness marker, and DKK1, a potent Wingless [WNT] inhibitor.

CONCLUSIONS

These cell cultures may provide a valuable in vitro and in vivo model to investigate mesothelioma biology. The identification of new mesothelioma markers may be useful for diagnosis and/or prognosis of this neoplasia as well as for isolation of mesothelioma tumor initiating cells.

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.

A conditional mouse model for malignant mesothelioma

Malignant mesothelioma is a devastating disease that has been associated with loss of Neurofibromatosis type 2 (NF2) and genetic lesions affecting RB and P53 pathways. We introduced similar lesions in the mesothelial lining of the thoracic cavity of mice. Mesothelioma developed at high incidence in Nf2;Ink4a/Arf and Nf2;p53 conditional knockout mice with median survival times of approximately 30 and 20 weeks, respectively. Murine mesothelioma closely mimicked human malignant mesothelioma. Conditional Nf2;Ink4a/Arf mice showed increased pleural invasion compared to conditional Nf2;p53 mice. Interestingly, upon Ink4a loss in the latter mice median survival was significantly reduced and all tumors were highly invasive, suggesting that Ink4a loss substantially contributes to the poor clinical outcome of malignant mesothelioma.

Characterization of human mesothelioma cell lines as tumor models for suicide gene therapy

BACKGROUND

The median survival time of patients with malignant pleural mesothelioma (MPM) remains poor. Therefore, novel therapeutic options are in high demand, and well characterized model systems for in vitro/vivo screening have to be established.

MATERIAL AND METHODS

For this purpose, 3 MPM cell lines (H-Meso-1, MSTO211H, and NCI-H28) were characterized and tested for susceptibility to recombinant adeno-associated virus 2 (rAAV2)-based vectors which have the potential for a loco-regional application.

RESULTS

Using multiplex fluorescence in situ hybridization, several recurrent chromosomal aberrations were observed for each of the MPM cell lines. Tumorigenicity of H-Meso-1 and MSTO-211H cells was shown in an intraperitoneal NOD/SCID mouse model, whereas NCI-H28 cells did not yield any tumors. Although all 3 cell lines were readily susceptible to rAAV2 vectors, differences in susceptibility were observed (H-Meso-1 > NCI-H28 > MSTO-211H). Furthermore, the efficacy of a potential suicide gene therapy using an rAAV2 suicide vector-transduced MPM cell line was determined in a proof-of-feasibility in vivo experiment.

CONCLUSION

The characterized cell lines described here may serve as a model for in vitro and in vivo preclinical gene therapy for the treatment of MPM using rAAV2 suicide vectors.

SYT-SSX fusion is absent in sarcomatoid mesothelioma allowing its distinction from synovial sarcoma of the pleura

The diagnosis of sarcomatoid mesothelioma is still a worldwide challenge and it is often difficult, both clinically and by morphological analysis, to differentiate sarcomatoid mesothelioma from synovial sarcoma, the most frequent intrathoracic sarcoma. To confirm the absence of the synovial sarcoma translocation t(X; 18) (SYT-SSX) in sarcomatoid mesothelioma, and to test its usefulness differentiating sarcomatoid mesothelioma from synovial sarcoma, 28 tumours were examined using the reverse transcriptase-polymerase chain reaction. RNA was extracted from paraffin blocks using standard methods, reverse-transcribed and PCR performed. Molecular analysis completed in two independent laboratories showed that sarcomatoid mesothelioma samples were negative for the t(X-18). This result confirms the usefulness of this analysis in differentiating sarcomatoid mesothelioma from synovial sarcoma.

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.

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.

Biologic, cytogenetic, and molecular factors in mesothelial proliferations

Although mesothelioma cases may have peaked in the 1990s in developed countries, it is expected that there will be over 70,000 cases diagnosed in the United States over the next 5 decades. With the industrial expansion in Southeast Asia and China and the continued use of asbestos, an epidemic of mesothelioma cases is anticipated over the next several decades. A considerable amount has been learned about the cytogenetic and molecular genetics of mesotheliomas. However, in-depth studies are needed to further define specific factors that may provide for early diagnosis, surgical treatment, oncologic management, and gene therapy. Serologic markers for surveillance of those with asbestos exposure and at risk for mesothelioma are needed. Targeted therapy using molecular markers and gene therapy may provide a means to reverse mesothelial proliferations or stabilize tumor growth and allow for surgical resection. The future holds great promise in identifying mesothelioma gene expression profiles (genomics, gene microarrays) and proteins (proteomics) that may produce the key to dealing with this dismal and devastating neoplasm.

Mitogen-activated protein kinase expression and activation does not differentiate benign from malignant mesothelial cells

BACKGROUND

In vitro studies of malignant mesothelioma (MM) cells have suggested activation of mitogen-activated protein kinase (MAPK) in response to asbestos exposure. The objective of this study was to investigate protein expression (level) and phosphorylation status (activity) of the extracellular-regulated kinase (ERK), the c-Jun amino-terminal kinase (JNK), and the high-osmolarity glycerol response kinase (p38) in vivo through the analysis of fresh frozen reactive mesothelium (RM) and MM specimens.

METHODS

MAPK levels were analyzed in 36 fresh-frozen MM specimens (32 effusions, 4 biopsies) and in 14 RM specimens (all effusions) using immunoblotting with antibodies detecting the total (pan-) and activated (phospho-) fraction (p-) of ERK, JNK, and p38. Values for pan-MAPK and p-MAPK expression and the p-MAPK/pan-MAPK ratio in MM and RM specimens were compared. Results were corroborated using immunocytochemistry for p-ERK, p-JNK, and p-38 in selected specimens.

RESULTS

Pan-ERK, pan-JNK, and pan-p38 expression was found frequently in both MM specimens (35 of 36 specimens) and RM specimens (14 of 14 specimens) using immunoblotting, with comparable findings for activated p-p38 (34 of 36 MM specimens, 13 of 14 RM specimens). Activation of p-ERK (27 of 36 MM specimens, 10 of 14 RM specimens) and p-JNK (25 of 36 MM specimens, 10 of 14 RM specimens) was less frequent. Pan-ERK (P = 0.016), pan-JNK (P = 0.004), pan-p38 (P = 0.012), and p-ERK (P = 0.02) expression levels were higher in MM specimens from female patients. Pan-p38 expression levels also were higher in peritoneal MM specimens (P = 0.019). MM and RM showed similar MAPK expression, activation, and activation ratios (Mann-Whitney test; P > 0.05). Immunocytochemistry localized MAPK to MM and RM cells.

CONCLUSIONS

The current results provided the first evidence of in vivo activation of MAPK in clinical MM and RM. The similar values in these two cell types suggest that MAPK may not be involved in the transformation of benign to malignant mesothelium, thus bringing into question the validity of using MAPKs as molecular therapeutic targets in patients with MM.

A Molecular Epidemiology Case Control Study on Pleural Malignant Mesothelioma

Pleural malignant mesothelioma is an uncommon neoplasm usually associated with asbestos exposure. The increasing incidence of malignant mesothelioma cases involving individuals with low levels of asbestos exposure suggests a complex carcinogenetic process with the involvement of other cofactors. Cytogenetic studies revealed the complexity of the genetic changes involved in this neoplasm reflecting the accumulation of genomic damage. One of the most used methodologies for assessing genomic damage is the cytokinesis-blocked micronucleus test applied in peripheral blood lymphocytes (PBL). This approach allows the detection of chromosomal alterations expressed in binucleated cells after nuclear division in vitro. This marker could provide a tool for assessing genetically determined constitutional differences in chromosomal instability. A biomonitoring study was carried out to evaluate the micronuclei frequency in PBLs of patients with pleural malignant mesothelioma with respect to lung cancer, healthy, and risk controls as a marker of cancer susceptibility in correlation with the presence of SV40. A significant increased micronuclei frequency was observed in patients with malignant mesothelioma in comparison with all the other groups, the mean micronuclei frequency was double in patients with malignant mesothelioma compared with healthy controls, risk controls, and patients with lung adenocarcinoma (median 11.4 binucleated cells with micronuclei/1,000 binucleated cells versus 6.2, 6.1, and 5.1, respectively). Our data indicate that human T lymphocyte samples carry DNA sequences coding for SV40 large T antigen at low prevalence, both in cancer cases and controls. Evidence of cytogenetic damage revealed as micronuclei frequency in mesothelioma cancer patients could be related to exogenous and endogenous cofactors besides asbestos exposure.

Differential expression of the 67 kilodalton laminin receptor in epithelioid malignant mesothelioma and carcinomas that spread to serosal cavities

Expression of the 67-kd laminin receptor (67-kd LR) has been reported in a wide range of carcinomas, in many of which it correlated with poor differentiation, metastasis, disease progression, and poor survival. Malignant mesothelioma (MM) is a locally aggressive and highly lethal tumor of serosal cavities that is rarely associated with clinically detectable metastasis to distant organs. The aim of this study was to analyze the expression of the 67-kd LR in epithelioid MM and carcinomas in effusions. Effusions from patients diagnosed with ovarian (=24) and breast (=38) adenocarcinomas and MM (=24) (total = 86) were analyzed for 67-kd LR protein expression, using immunocytochemistry. The 67-kd LR mRNA expression was additionally analyzed in 21 MM effusions using reverse transcription-polymerase chain reaction (RT-PCR). Protein expression of the 67-kd LR was frequently detected in carcinomas (19/24 ovarian tumors, 79%; 15/38 breast tumors, 39%), but was rare in MM (2/24 cases, 8%), despite the presence of mRNA transcripts for the receptor in all 21 specimens studied using RT-PCR. Nine benign effusions that were additionally studied for protein expression were uniformly negative, as were all reactive mesothelial cells in malignant effusions. Our results suggest that the 67-kd LR may aid in the differential diagnosis between metastatic carcinoma, mainly of ovarian origin, and MM. They additionally suggest that the failure of MM to express the 67-kd LR protein, as opposed to the frequent expression in carcinomas with proven metastatic capacity, may be one of the factors contributing to the reduced ability of the former tumor to metastasize to distant organs.

Aberrant methylation profile of human malignant mesotheliomas and its relationship to SV40 infection

Malignant mesothelioma (MM) is associated with asbestos exposure and the presence of SV40 viral sequences. Recently, we reported that SV40 infection of human mesothelial cells (HM) causes aberrant methylation of the tumor suppressor gene (TSG) RASSF1A. We investigated methylation of 12 genes by methylation-specific PCR in 63 MMs, six MM cell lines, and two foci of SV40-infected HM. Methylation percentages of the tested genes ranged from 3 to 65%. The frequencies of HPP1, RASSF1A, Cyclin D2, and RRAD methylation, and the value of the methylation index, were significantly higher in SV40 sequence-positive MMs than in SV40-negative MMs. Methylation of TMS1 and HIC-1 was associated with shortened survival. SV40-infected HM showed progressive aberrant methylation of seven genes (RASSF1A, HPP1, DcR1, TMS1, CRBP1, HIC-1, and RRAD) during serial passage. Our results demonstrate a relationship between SV40 and methylation of multiple genes in MM, indicating that the virus plays a role in the pathogenesis of MM.

Heparanase and basic fibroblast growth factor are co-expressed in malignant mesothelioma

Heparanase is an endoglycosidase that degrades heparan sulfate (HS) in the extracellular matrix (ECM) and cell surfaces, and fulfills a significant role in cancer metastasis and angiogenesis. We evaluated the expression of heparanase and its possible association with the expression of angiogenic molecules in malignant mesothelioma (MM), and analyzed whether expression of these proteins is site-related (pleural vs peritoneal MM, solid lesions vs effusions). Sections from 80 MM (56 biopsies, 24 effusions) were analyzed for heparanase protein expression using immunohistochemistry (IHC). Sixty MM were of pleural origin, and 20 were peritoneal. Effusion specimens consisted of 6 peritoneal and 18 pleural effusions, while biopsies consisted of 14 peritoneal and 42 pleural lesions. Fifty-four specimens were additionally evaluated for expression of basic fibroblast growth factor (bFGF), interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF) proteins using IHC. Microvessel density (MVD) was studied in 28 biopsies using an anti-CD31 antibody. mRNA expression of heparanase (HPSE-1), VEGF and the VEGF receptor KDR was analyzed in 23 effusions using RT-PCR. Heparanase protein expression was seen in 69/80 (86%) tumors. Of these, 35 showed combined membrane and cytoplasmic expression, 30 cytoplasmic expression, and four exclusively membrane expression. Both total (P = 0.001) and cytoplasmic (P = 0.002) expression was significantly higher in solid tumors compared to effusions. Protein expression of VEGF, IL-8 and bFGF was seen in 21/54 (39%), 22/54 (41%) and 44/54 (81%) specimens, respectively. Protein expression of bFGF was significantly higher in solid tumors (P < 0.001) and correlated with heparanase expression (P = 0.005). HPSE-1 and VEGF mRNA expression was detected in all 23 effusions using RT-PCR, while KDR mRNA was found in 12/23 MM. KDR mRNA expression correlated with that of both HPSE-1 (P = 0.005) and VEGF (P = 0.001). Our results document frequent expression of heparanase in MM, in agreement with the biological aggressiveness of this tumor. The co-expression of heparanase with bFGF is in agreement with the role of the former in releasing bFGF from the ECM. The concomitant reduction in protein expression of both molecules in effusions as compared to solid tumors, supports the hypothesis of a reduced need for pro-angiogenic stimuli in effusions, and may aid in defining tumor progression in this setting.

Expression of the nerve growth factor receptors TrkA and p75 in malignant mesothelioma

The objective of the present report was to study the expression of the low affinity nerve growth factor (NGF) receptor p75 and of the activated high-affinity NGF receptor TrkA in malignant mesothelioma (MM). In addition, to analyze whether expression of these receptors is site-related (pleural versus peritoneal MM, solid lesions versus effusions). Sections from 81 MM (57 biopsies, 24 effusions) were analyzed. Sixty-one mesotheliomas were of pleural origin, while the remaining 20 were peritoneal. Effusion specimens consisted of 6 peritoneal and 18 pleural effusions, while biopsies consisted of 14 peritoneal and 43 pleural lesions. Specimens were immunohistochemically stained using antibodies against p75 and phospho-TrkA (p-TrkA). Six effusions were additionally analyzed for p-TrkA expression using immunoblotting (IB). p-TrkA membrane expression (66/81 specimens; 81%) was by far more frequent than that of p75 (26/81 specimens; 32%). In addition, p-TrkA expression was significantly higher in peritoneal MM compared to their pleural counterparts (20/20 versus 46/61 positive tumors; P = 0.014). p-TrkA membrane expression was marginally higher in effusions (P = 0.058), while the opposite was true for p75 membrane expression (P = 0.008) and p-TrkA cytoplasmic expression (P = 0.003). In conclusion, our results document for the first time frequent expression of p-TrkA and lower expression of p75 in MM, in agreement with the biological aggressiveness of this tumor. The enhanced expression of p-TrkA in peritoneal MM, tumors that appear in younger patients, and in effusions as compared to solid tumors, suggest that p-TrkA plays a significant role in the biology of this disease and may aid in defining tumor progression in this setting.

Deciduoid mesothelioma in the pelvic cavity

A very rare case of deciduoid mesothelioma in the pelvic cavity is presented. A 24-year-old woman (gestational stage: 28 weeks and 6 days) was admitted because of a tumor mass in the abdominal cavity. A well-circumscribed and fibrously encapsulated tumor mass was revealed in the Douglas cavity. Histologically, tumor cells were arranged in a solid sheet with deciduoid appearance and showed partial glandular and papillary structures. The tumor cells contained PAS positive and diastase-digested granules in the cytoplasm as well as alcian-blue positive and hyaluronidase-digested substances in the stroma. The cellularity of the tumor cells was moderate and mitoses were rare. There was partial tumor necrosis and tumor cells had infiltrated through the fibrous capsule. Immunohistochemically, the tumor cells were reactive for pancytokeratin, cytokeratin5/6, vimentin, HBME-1, calretinin and thrombomodulin. Ultrastructurally, numerous, long microvilli, tonofilaments and desmosome junctions could be seen. Consequently, this case was diagnosed as deciduoid mesothelioma and 2 years and 4 months after operation, the patient's clinical course has been good. This case is considered to be the first reported in Japan.

Mechanisms of sarcoma development

Sarcomas are a rare and diverse group of tumours that are derived from connective tissues, including bone, muscle and cartilage. Although there are instances of hereditary predisposition to sarcomas, the overwhelming majority of such tumours are sporadic. In the past decade, we have gained much insight into the genetic abnormalities that seem to underlie the pathogenesis of these tumours. This information has already led to new classification of many sarcomas, as well as to successful therapies that are targeted at specific genetic abnormalities. It is likely that this approach will lead to continued refinements in classification and treatment of these tumours.

Malignant mesothelioma growth inhibition by agents that target the VEGF and VEGF-C autocrine loops

Malignant mesothelioma (MM) is a locally aggressive tumor that originates from the mesothelial cells of the pleural and sometimes peritoneal surface. Conventional treatments for MM, consisting of chemotherapy or surgery give little survival benefit to patients, who generally die within 1 year of diagnosis. Hence, there is an urgent need for the development of alternative therapies. Vascular endothelial growth factor (VEGF) is an autocrine growth factor for MM. The closely related molecule, VEGF-C, is also implicated in malignant mesothelioma growth. VEGF-C and its cognate receptor VEGFR-3 are co-expressed in mesothelioma cell lines. A functional VEGF-C autocrine growth loop was demonstrated in mesothelioma cells by targeting VEGF-C expression and binding to VEGFR-3. The ability of novel agents that reduce the levels of VEGF and VEGF-C to inhibit mesothelioma cell growth in vitro was assessed. Antisense oligonucleotide (ODN) complementary to VEGF that inhibited VEGF and VEGF-C expression simultaneously specifically inhibited mesothelioma cell growth. Similarly, antibodies to VEGF receptor (VEGFR-2) and VEGF-C receptor (VEGFR-3) were synergistic in inhibiting mesothelioma cell growth. In addition, a diphtheria toxin-VEGF fusion protein (DT-VEGF), which is toxic to cells that express VEGF receptors was very effective in inhibiting mesothelioma cell growth in vitro. These results indicate that targeting VEGF and VEGF-C simultaneously may be an effective therapeutic approach for malignant mesothelioma.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Cytogenetics and molecular genetics of bone and soft-tissue tumors

The cytogenetic and molecular findings in bone and soft-tissue sarcomas are summarized. A table presenting all such tumors, with their specific translocations and the genes involved, is included, along with a list of those tumors that most likely result from a stepwise process of numerous genetic changes.

Current therapy for malignant mesothelioma

This review briefly summarizes the results of previous systemic (chemotherapy) and local (surgery and radiotherapy) treatment attempted to date for malignant mesothelioma. The prospects for newer modalities, ie molecular and biologic therapies, are also highlighted, including results of both preclinical and early clinical research.