The pathological and molecular diagnosis of malignant pleural mesothelioma: a literature review

Exploring RNA cargo in extracellular vesicles for pleural mesothelioma detection

BACKGROUND

Pleural Mesothelioma (PM) is a highly aggressive cancer, for which effective early detection remains a challenge due to limited screening options and low sensitivity of biomarkers discovered so far. While extracellular vesicles (EVs) have emerged as promising candidates for blood-based biomarkers, their role in PM has not been studied yet. In this study, we characterized the transcriptomic profile of EVs secreted by PM primary cells and explored their potential as a biomarker source for PM detection.

METHODS

We collected cell culture supernatant from early-passage PM cell cultures derived from the pleural effusion of 4 PM patients. EVs were isolated from the supernatant using Qiagen exoEasy Maxi kit. RNA isolation from EVs was done using the mirVana PARIS kit. Finally, single-end RNA sequencing was done with Illumina Novaseq 6000.

RESULTS

We identified a range of RNA species expressed in EVs secreted by PM cells, including protein-coding RNA (80%), long non-coding RNA (13%), pseudogenes (4.5%), and short non-coding RNA (1.6%). We detected a subset of genes associated with the previously identified epithelioid (32 genes) and sarcomatoid molecular components (36 genes) in PM-EVs. To investigate whether these markers could serve as biomarkers for PM detection in blood, we compared the RNA content of PM-EVs with the cargo of EVs isolated from the plasma of healthy donors (publicly available data). Majority of upregulated genes in PM-EVs were protein-coding and long non-coding RNAs. Interestingly, 25 of them were the sarcomatoid and epithelioid marker genes. Finally, functional analysis revealed that the PM-EV RNA cargo was associated with Epithelial-Mesenchymal transition, glycolysis, and hypoxia.

CONCLUSIONS

This is the first study to characterize the transcriptomic profile of EVs secreted by PM primary cell cultures, demonstrating their potential as biomarker source for early detection. Further investigation of the functional role of PM-EVs will provide new insights into disease biology and therapeutic avenues.

Diagnostic Challenges in the Pathological Approach to Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) still represents a complex diagnostic challenge for pathologists in routine practice. This diagnosis requires a multidisciplinary approach, and pathological evaluation is mandatory. The histopathological diagnosis is stepwise and should be based on morphological and immunohistochemical assessment, sometimes associated with molecular tests, and supported by clinical and radiological findings. A correct morphological approach aims to exclude pleural metastasis or benign mesothelial proliferations, which are the main differential diagnoses. While certain histological features are diagnostic of MPM, others are highly suggestive but not definitive. Immunohistochemistry plays a pivotal role, with a panel of both traditional and newer markers being used to assess mesothelial differentiation and to differentiate malignant from benign proliferations. In more challenging cases, molecular tests, such as fluorescent in situ hybridization (FISH) to detect CDKN2A deletion, can be helpful in distinguishing malignant from benign pleural lesions. This review summarizes the key morphological, immunohistochemical, and molecular features that should be considered when pleural biopsy samples are examined, with the aim of improving diagnostic accuracy in this complex area.

Synchronous Pleural and Peritoneal Mesothelioma in a Free-Ranging Capuchin Monkey (Sapajus libidinosus)

A free-ranging capuchin monkey developed a synchronous biphasic pleural and peritoneal mesothelioma, a rare form of this tumor. Exophytic nodules were dispersed over the serosal surfaces, showing marked microscopical malignant features composed of both epithelioid and spindeloid neoplastic cells immunopositive for Pan-Cytokeratin, Cytokeratin 5/6, Vimentin, WT-1, and D2-40.

Real-world outcomes for patients with pleural mesothelioma: A multisite retrospective cohort study

AIM

To evaluate the real-world treatment patterns and outcomes for patients with pleural mesothelioma (PM) in the era of immunotherapy.

METHODS

This retrospective audit included patients with PM diagnosed within three tertiary referral centers in Queensland, Australia from January 2017 to July 2023. Patient and treatment characteristics and outcomes were recorded. Data was analyzed using descriptive statistics and the Kaplan-Meier survival method.

RESULTS

A total of 90 patients were included: 84% were male, the median age was 75 years (range 70-79) and 85% had baseline Eastern Group Cooperative Group of 0-1. Subtypes included 54% epithelioid, 17% biphasic, 12% sarcomatoid, and 17% unspecified/unknown. First-line treatment was received by 57/90 patients (63%) and 33/90 patients (37%) received the best supportive care (BSC). Chemotherapy was most used (63%) overall, but first-line immunotherapy was more commonly used since ipilimumab/nivolumab was reimbursed by the Australian Pharmaceutical Benefits Scheme in July 2021. After first-line treatment, only 40% received second-line treatment and 60% received BSC. 12-month overall survival (OS) and progression-free survival for all patients were 53% (95% confidence interval [CI]: 43-65) and 25% (95% CI 15-40) respectively. 12-month OS was 72%, 64%, and 29% for immunotherapy, chemotherapy, and BSC, respectively. There was no significant difference in survival between chemotherapy and immunotherapy (hazard ratio 1.28, 95% CI: 0.65-2.5, p = 0.5).

CONCLUSION

In our unselected real-world cohort, both chemotherapy and immunotherapy are active against PM, but the prognosis remains guarded. There remains a need for better treatment options, especially in the first-line setting. Enrolment in clinical trials is crucial to improving outcomes in this debilitating disease.

ERS statement on benign pleural effusions in adults

The incidence of non-malignant pleural effusions far outweighs that of malignant pleural effusions and is estimated to be at least 3-fold higher. These so-called benign effusions do not follow a "benign course" in many cases, with mortality rates matching and sometimes exceeding those of malignant pleural effusions. In addition to the impact on patients, healthcare systems are also significantly affected, with recent US epidemiological data demonstrating that 75% of resource allocation for pleural effusion management is spent on non-malignant pleural effusions (excluding empyema). Despite this significant burden of disease, and by existing at the junction of multiple medical specialties, reflecting a heterogenous constellation of medical conditions, non-malignant pleural effusions are rarely the focus of research or the subject of management guidelines. With this European Respiratory Society Task Force, we assembled a multispecialty collaborative across 11 countries and three continents to provide a statement based on systematic searches of the medical literature to highlight evidence in the management of the following clinical areas: a diagnostic approach to transudative effusions, heart failure, hepatic hydrothorax, end-stage renal failure, benign asbestos-related pleural effusion, post-surgical effusion and nonspecific pleuritis.

Development of mesothelioma-specific oncolytic immunotherapy enabled by immunopeptidomics of murine and human mesothelioma tumors

Malignant pleural mesothelioma (MPM) is an aggressive tumor with a poor prognosis. As the available therapeutic options show a lack of efficacy, novel therapeutic strategies are urgently needed. Given its T-cell infiltration, we hypothesized that MPM is a suitable target for therapeutic cancer vaccination. To date, research on mesothelioma has focused on the identification of molecular signatures to better classify and characterize the disease, and little is known about therapeutic targets that engage cytotoxic (CD8+) T cells. In this study we investigate the immunopeptidomic antigen-presented landscape of MPM in both murine (AB12 cell line) and human cell lines (H28, MSTO-211H, H2452, and JL1), as well as in patients' primary tumors. Applying state-of-the-art immuno-affinity purification methodologies, we identify MHC I-restricted peptides presented on the surface of malignant cells. We characterize in vitro the immunogenicity profile of the eluted peptides using T cells from human healthy donors and cancer patients. Furthermore, we use the most promising peptides to formulate an oncolytic virus-based precision immunotherapy (PeptiCRAd) and test its efficacy in a mouse model of mesothelioma in female mice. Overall, we demonstrate that the use of immunopeptidomic analysis in combination with oncolytic immunotherapy represents a feasible and effective strategy to tackle untreatable tumors.

Characterizing the distribution of alterations in mesothelioma and their correlation to morphology

OBJECTIVES

Mesothelioma is a lethal disease that arises from the serosal lining of organ cavities. Several recurrent alterations have been observed in pleural and peritoneal -mesotheliomas, including in BAP1, NF2, and CDKN2A. Although specific histopathologic parameters have been correlated with prognosis, it is not as well known whether genetic alterations correlate with histologic findings.

METHODS

We reviewed 131 mesotheliomas that had undergone next-generation sequencing (NGS) at our institutions after pathologic diagnosis. There were 109 epithelioid mesotheliomas, 18 biphasic mesotheliomas, and 4 sarcomatoid mesotheliomas. All our biphasic and sarcomatoid cases arose in the pleura. Of the epithelioid mesotheliomas, 73 were from the pleura and 36 were from the peritoneum. On average, patients were 66 years of age (range, 26-90 years) and predominantly male (92 men, 39 women).

RESULTS

The most common alterations identified were in BAP1, CDKN2A, NF2, and TP53. Twelve mesotheliomas did not show a pathogenic alteration on NGS. For epithelioid mesotheliomas in the pleura, the presence of an alteration in BAP1 correlated with low nuclear grade (P = .04), but no correlation was found in the peritoneum (P = .62). Similarly, there was no correlation between the amount of solid architecture in epithelioid mesotheliomas and any alterations in the pleura (P = .55) or peritoneum (P = .13). For biphasic mesotheliomas, cases with either no alteration detected or with an alteration in BAP1 were more likely to be epithelioid predominant (>50% of the tumor, P = .0001), and biphasic mesotheliomas with other alterations detected and no alteration in BAP1 were more likely to be sarcomatoid predominant (>50% of the tumor, P = .0001).

CONCLUSIONS

This study demonstrates a significant association between morphologic features associated with a better prognosis and an alteration in BAP1.

Highlighting the immunohistochemical differences of malignant mesothelioma subtypes via case presentations

Malignant mesothelioma (MM) is a rare tumor of mesothelial cells, with an increasing incidence both in developed and developing countries. MM has three major histological subtypes, in order of frequency, according to the World Health Organization (WHO) Classification of 2021: epithelioid, biphasic, and sarcomatoid MM. Distinction may be a challenging task for the pathologist, due to the unspecific morphology. Here, we present two cases of diffuse MM subtypes to emphasize the immunohistochemical (IHC) differences, and to facilitate diagnostic difficulties. In our first case of epithelioid mesothelioma, the neoplastic cells showed cytokeratin 5/6 (CK5/6), calretinin, and Wilms-tumor-1 (WT1) expression, while remaining negative with thyroid transcription factor-1 (TTF-1). BRCA1 associated protein-1 (BAP1) negativity was seen in the neoplastic cells' nucleus, reflecting loss of the tumor suppressor gene. In the second case of biphasic mesothelioma, expression of epithelial membrane antigen (EMA), CKAE1/AE3, and mesothelin was observed, while WT1, BerEP4, CD141, TTF1, p63, CD31, calretinin, and BAP1 expressions were not detected. Due to the absence of specific histological features, the differentiation between MM subtypes could be a challenging task. In routine diagnostic work, IHC may be the proper method in distinction. According to our results and literature data, CK5/6, mesothelin, calretinin, and Ki-67 should be applied in subclassification.

Excess of blood eosinophils prior to therapy correlates with worse prognosis in mesothelioma

Background

Only a fraction of patients with malignant pleural mesothelioma (MPM) will respond to chemo- or immunotherapy. For the majority, the condition will irremediably relapse after 13 to 18 months. In this study, we hypothesized that patients' outcome could be correlated to their immune cell profile. Focus was given to peripheral blood eosinophils that, paradoxically, can both promote or inhibit tumor growth depending on the cancer type.

Methods

The characteristics of 242 patients with histologically proven MPM were retrospectively collected in three centers. Characteristics included overall survival (OS), progression-free survival (PFS), overall response rate (ORR) and disease control rate (DCR). The mean absolute eosinophil counts (AEC) were determined by averaging AEC data sets of the last month preceding the administration of chemo- or immunotherapy.

Results

An optimal cutoff of 220 eosinophils/µL of blood segregated the cohort into two groups with significantly different median OS after chemotherapy (14 and 29 months above and below the threshold, p = 0.0001). The corresponding two-year OS rates were 28% and 55% in the AEC ≥ 220/µL and AEC < 220/µL groups, respectively. Based on shorter median PFS (8 vs 17 months, p < 0.0001) and reduced DCR (55.9% vs 35.2% at 6 months), the response to standard chemotherapy was significantly affected in the AEC ≥ 220/µL subset. Similar conclusions were also drawn from data sets of patients receiving immune checkpoint-based immunotherapy.

Conclusion

In conclusion, baseline AEC ≥ 220/µL preceding therapy is associated with worse outcome and quicker relapse in MPM.

Clinical, Laboratory, Histological, Radiological, and Metabolic Features and Prognosis of Malignant Pleural Mesothelioma

Background: Malignant pleural mesothelioma (MPM) is an aggressive and rare malignant pleural tumor. Methods: MPM patients diagnosed in Beijing Chaoyang Hospital and Beijing Tongren Hospital were the focus of this study. We collected and analyzed the histological, radiological, and metabolic features of MPM patients. At the same time, Cox univariable and multivariable analyses were used to explore the laboratory risk factors affecting the prognosis of MPM patients. Results: A total of 129 MPM patients were included in this study. MPM includes three main histological subtypes: epithelioid, sarcomatoid and biphasic. Among them, epithelial subtypes accounted for the highest proportion. Calretinin, Wilms' tumor gene (WT1), cytokeratin 5/6 (CK5/6), and D2-40 were the most useful mesothelial markers to support a MPM diagnosis. The imaging features of MPM patients are pleural thickening and pleural effusion. In PET-CT, the affected pleura showed obvious high uptake of tracer, and the degree was related to the specific subtype. The median follow-up time was 55.0 (30.0, 94.0) months. A total of 92 (71.3%) patients died during follow-up. The median survival time of patients was 21.0 (9.0, 48.0) months. The Cox multivariable analysis showed that age [hazard ratio (HR), 1.824; 95% confidence interval (CI) 1.159-2.872; p = 0.009; uncorrected], ESR (HR, 2.197; 95% CI 1.318-3.664; p = 0.003; with Bonferroni correction), lymphocytes (HR, 0.436; 95% CI 0.258-0.737; p = 0.002; with Bonferroni correction), platelets (HR, 1.802; 95% CI 1.084-2.997; p = 0.023; uncorrected) and total protein (HR, 0.625; 95% CI 0.394-0.990; p = 0.045; uncorrected) were independent risk factors for prognosis, after adjusting for confounding factors. Conclusions: Age, ESR, lymphocytes, platelets and total protein may be related to the prognosis of MPM patients. Summarizing the histological, radiological, and metabolic features of MPM patients in the two centers can increase clinicians' understanding of this rare tumor.

Outcome of dogs treated with chemotherapy for mesothelioma: A retrospective clinical study on 40 cases and a literature review

Mesothelioma is an uncommon cancer in dogs for which there is no established standard of care. Chemotherapy is often suggested despite no definitive proof of efficacy. The aim of this study was to evaluate the impact of chemotherapy on survival of dogs with mesothelioma. A retrospective multicentric study was carried out. To be included, dogs needed to present an evocative clinical evolution and a morphological diagnosis of mesothelioma. Exclusion of other cause of effusion and complete clinical follow-up were also required. Fourty dogs were included, 27 received chemotherapy (group 1) and 13 did not (group 2). Groups were heterogeneous regarding the proportion of animals undergoing surgery as part of their treatment (16 in group 1, 2 in group 2; p = .016) and homogeneous otherwise. Univariate analysis showed that dogs from group 1 survived significantly longer than dogs from group 2 (MST: 366 vs. 74 days; p < .001). Complete resolution of effusion after the first chemotherapy administration positively correlated with survival in group 1 (MST: 415 vs. 160 days; p < .01). All other variable tested had no significant impact on survival in univariate analysis, but dogs undergoing surgery and dogs having serous membranes' modification at medical imaging tended to survive longer. Multivariate analysis confirmed that chemotherapy was the sole variable independently associated with survival in our study (odds ratio 5.57-6.12; p < .01).

Near Missed Case of Occupational Pleural Malignant Mesothelioma, a Case Report and Latest Therapeutic Options

Asbestos use started to be gradually banned in Europe from 1991 onwards, and there are currently strict occupational exposure limits for asbestos. However, malignant mesothelioma has a long latency time (in some cases up to 50-60 years), so the risks related to asbestos exposure should not be forgotten. Considering the increased risk of lung cancer following the inhalation of asbestos fibers, lifetime health monitoring should be considered in people occupationally exposed to asbestos, with an emphasis on the respiratory system. An assessment of their occupational history should be performed rigorously, especially in the areas with a history of asbestos production/use, as this is a key element for an early diagnosis and appropriate treatment. This case report presents a near-missed case of occupational pleural malignant mesothelioma. The latency time between the first asbestos exposure and the diagnosis of occupational pleural malignant mesothelioma was 49 years. The accurate diagnosis was made two years after the first symptoms appeared.

Epigenetic Immune Remodeling of Mesothelioma Cells: A New Strategy to Improve the Efficacy of Immunotherapy

Malignant pleural mesothelioma (MPM) is an aggressive malignancy with a severe prognosis, and with a long-standing need for more effective therapeutic approaches. However, treatment with immune checkpoint inhibitors is becoming an increasingly effective strategy for MPM patients. In this scenario, epigenetic modifications may negatively regulate the interplay between immune and malignant cells within the tumor microenvironment, thus contributing to the highly immunosuppressive contexture of MPM that may limit the efficacy of immunotherapy. Aiming to further improve prospectively the clinical efficacy of immunotherapeutic approaches in MPM, we investigated the immunomodulatory potential of different classes of epigenetic drugs (i.e., DNA hypomethylating agent (DHA) guadecitabine, histone deacetylase inhibitors VPA and SAHA, or EZH2 inhibitors EPZ-6438) in epithelioid, biphasic, and sarcomatoid MPM cell lines, by cytofluorimetric and real-time PCR analyses. We also characterized the effects of the DHA, guadecitabine, on the gene expression profiles (GEP) of the investigated MPM cell lines by the nCounter platform. Among investigated drugs, exposure of MPM cells to guadecitabine, either alone or in combination with VPA, SAHA and EPZ-6438 demonstrated to be the main driver of the induction/upregulation of immune molecules functionally crucial in host-tumor interaction (i.e., HLA class I, ICAM-1 and cancer testis antigens) in all three MPM subtypes investigated. Additionally, GEP demonstrated that treatment with guadecitabine led to the activation of genes involved in several immune-related functional classes mainly in the sarcomatoid subtype. Furthermore, among investigated MPM subtypes, DHA-induced CDH1 expression that contributes to restoring the epithelial phenotype was highest in sarcomatoid cells. Altogether, our results contribute to providing the rationale to develop new epigenetically-based immunotherapeutic approaches for MPM patients, potentially tailored to the specific histologic subtypes.

Treatment patterns and outcomes for patients with malignant pleural mesothelioma in England in 2013-2017: A nationwide CAS registry analysis from the I-O Optimise initiative

OBJECTIVES

Malignant pleural mesothelioma (MPM) is a rare and aggressive cancer with a poor prognosis and limited treatment options. This study assessed the characteristics, treatment patterns, and outcomes for patients diagnosed with MPM in England.

MATERIALS AND METHODS

As part of I-O Optimise, this retrospective cohort study analyzed data recorded in the Cancer Analysis System in England for all adult patients newly diagnosed with MPM between 2013 and 2017, with follow-up to March 2018 or death, whichever occurred first. Overall survival (OS) was estimated using Kaplan-Meier methods. A Cox regression model was used to describe the impact of sociodemographic and clinical characteristics at diagnosis on OS.

RESULTS

9458 patients diagnosed with MPM were analyzed. Median age at diagnosis was 75 years; 83.4% were male. Eastern Cooperative Oncology Group performance status (ECOG PS) was 0-1 for 44.5%; 2 for 11.5%; >2 for 9.1%; and missing for 34.9% of patients. TNM stage was missing for 60.4%. A majority of patients had epithelioid histology (36.4%) or not otherwise specified (NOS) MPM (43.3%). After diagnosis, 48.7% of all patients received best supportive care (BSC; no surgery, radiotherapy, SACT); 11.4% received palliative radiotherapy alone; 6.5% underwent surgery; 33.4% received systemic anticancer therapy (SACT) as initial treatment. Platinum plus pemetrexed was the main SACT regimen used in both first and second line. Median OS (8.3 months) varied by histopathology and ranged from 4.3 to 13.3 months for sarcomatoid and epithelioid MPM, respectively. After adjusting for age, sex, and ECOG PS, sarcomatoid, biphasic, and NOS MPM remained significantly associated with worse OS than epithelioid MPM (all p < 0.001). Median OS varied from 4.6 to 17.0 months for patients receiving BSC/palliative radiotherapy, and patients receiving surgery, respectively.

CONCLUSION

Outcomes for patients with MPM in England remain poor. Future studies will investigate the impact of newer therapies on the treatment patterns and survival of MPM patients.

A Rare Case of Malignant Pleural Mesothelioma in a Young Healthy Male Without Asbestos Exposure

Malignant pleural mesothelioma (MPM) is a highly aggressive malignant tumor that arises from mesothelial cells of pleural cavity. The main risk factor for MPM is asbestos exposure with most cases discovered in elderly males after a long latency period. However, here we report a rare case of MPM diagnosed in a healthy young male patient without significant asbestos exposure.

We report the case of an otherwise healthy 47-year-old male who presented with one week of exertional dyspnea and chest pain. Chest X-ray showed unilateral large pleural effusion. Chest CT scan revealed confluent right hilar mass and pleural thickening. Pleural fluid analysis showed exudative features. Cytology was negative for malignant cells. Core tissue biopsy showed features of epithelioid mesothelioma.

Although most cases of MPM have been reported in elderly male patients with significant asbestos exposure, more research is needed to explain the pathogenesis of MPM in young patients without asbestos exposure.

Tumor Treating Fields (TTFields) downregulate the Fanconi Anemia-BRCA pathway and increase the efficacy of chemotherapy in malignant pleural mesothelioma preclinical models

OBJECTIVES

Tumor Treating Fields (TTFields) are low intensity, intermediate frequency, alternating electric fields with antimitotic effects on cancerous cells. TTFields concomitant with pemetrexed and a platinum agent are approved in the US and EU as first line therapy for unresectable, locally advanced or metastatic malignant pleural mesothelioma (MPM). The goal of the current study was to characterize the mechanism of action of TTFields in MPM cell lines and animal models.

METHODS

Human MPM cell lines MSTO-211H and NCI-H2052 were treated with TTFields to determine the frequency that elicits maximal cytotoxicity. The effect of TTFields on DNA damage and repair, and the cytotoxic effect of TTFields in combination with cisplatin and/or pemetrexed were examined. Efficacy of TTFields concomitant with cisplatin and pemetrexed was evaluated in orthotopic IL-45 and subcutaneous RN5 murine models.

RESULTS

TTFields at a frequency of 150 kHz demonstrated the highest cytotoxicity to MPM cells. Application of 150 kHz TTFields resulted in increased formation of DNA double strand breaks, elevated expression of DNA damage induced cell cycle arrest proteins, and reduced expression of Fanconi Anemia (FA)-BRCA DNA repair pathway proteins. Co-treatment of TTFields with cisplatin or pemetrexed significantly increased treatment efficacy versus each modality alone, with additivity and synergy exhibited by the TTFields-pemetrexed and TTFields-cisplatin combinations, respectively. In animal models, tumor volume was significantly lower for the TTFields-cisplatin-pemetrexed combination compared to control, accompanied by increased DNA damage within the tumor.

CONCLUSION

This research demonstrated that the efficacy of TTFields for the treatment of MPM is associated with reduced expression of FA-BRCA pathway proteins and increased DNA damage. This mechanism of action is consistent with the observed synergism for TTFields-cisplatin vs additivity for TTFields-pemetrexed, as cisplatin-induced DNA damage is repaired via the FA-BRCA pathway.

Sarcomatoid Mesothelioma: A Clinicopathological and Immunohistochemical Study of 64 Cases

Sixty-four cases of sarcomatoid pleural mesothelioma represent the basis of this study. The patients are 51 men and 13 women between the ages of 42 and 79 years, who presented with symptoms of chest pain, cough, and weight loss. Diagnostic imaging showed the presence of diffuse pleural thickening with encasement of the lung parenchyma in all the cases. All patients had surgical resection via extrapleural pneumonectomy. By immunohistochemistry, all cases were positive for cytokeratin AE1/AE3; however, reactivity with other markers including keratin 5/6, calretinin, and D2-40 was seen in different proportions, whereas a few cases showed positive staining for GATA3, WT1, and p40. All tumors were negative for carcinomatous epitopes (carcinoembryonic antigen, CD15, and TTF1). Our findings show that even though the use of immunohistochemical stains plays an important role in the final interpretation, the best results are accomplished by a global interpretation of clinical, radiographical, and immunohistochemical findings. It is also important to highlight that it does not seem to be a single immunohistochemical stain that is pathognomonic of sarcomatoid mesothelioma and that some other stains that are commonly used for other tumors may also show positive staining in a small percentage of sarcomatoid mesotheliomas.

The International System for Reporting Serous Fluid Cytopathology: How to Incorporate Molecular Data in Cytopathology Reports

Serous effusion cytology is widely employed in the initial evaluation of the etiology of effusions with a high diagnostic sensitivity. To standardize practices, The International System for Reporting Serous Fluid Cytology (TIS) was developed following best international practices, the most up-to-date literature, and expert consensus. In the context of this system, ancillary techniques play an important role. Besides defining basic principles in laboratory specimen handling, adequacy criteria, and a standardized reporting terminology with five diagnostic categories, TIS provides an actionable framework for using immunohistochemical and molecular testing in effusion samples, namely, in atypical, suspicious of malignant samples. For diagnostic purposes, these tests may be employed to distinguish between a primary and secondary neoplasm, to confirm a diagnosis of malignant mesothelioma vs. reactive mesothelial hyperplasia, and to correctly classify and determine the primary location of a metastasis. Theranostic molecular tests may also be used for these samples to evaluate potential therapeutic targets. Pathologists play a central role in guiding this process by determining adequacy and selecting appropriate ancillary tests. The activity in this area of research should increase in the near future as new therapeutic targets are discovered and new drugs enter the clinical practice.

Metastasis of Sarcomatoid Malignant Mesothelioma With p16/CDKN2A Deletion Manifested as a Subcutaneous Mass in the Back: A Case Report and Review of Literature

Sarcomatoid malignant mesothelioma (MM) is a rare and aggressive disease, and its diagnosis is challenging. A 60-year-old man presented with a recurrent subcutaneous mass in his right back after the initial resection. A chest computed tomography (CT) scan found right pleural thickening, nodular pleural thickening, pleural effusion, mediastinal, and right infraclavicular lymph nodes enlargement, which indicated a right pleura MM. Immunohistochemical stains of the resected mass showed sarcomatous atypical spindle cells, which were positive for pan-CKs (clone Anti-cytokeratin cocktail AE1/AE3), cytokeratin 5/6 (CK5/6), Wilm's tumor 1, podoplanin, vimentin and programmed death-ligand 1 (PD-L1), and negative for Napsin A, thyroid transcription factor 1, CDX 2, calretinin and desmin, and fluorescent in situ hybridization detected homozygous p16/cyclin-dependent kinase inhibitor 2A (p16/CDKN2A) deletion. The association of the chest CT features and the pathological assessment confirmed metastatic MM in the subcutaneous layer of the back. Moreover, positron emission tomography-CT showed multiple metastases in his brain. He developed massive right pleural effusion and chest tightness soon, and the mass kept growing despite local and systemic treatments. The patient die of pulmonary failure in 3 months.

Identification of Redox-Sensitive Transcription Factors as Markers of Malignant Pleural Mesothelioma

Simple Summary

Malignant pleural mesothelioma is a lung tumor associated with asbestos exposure, with a poor prognosis, and a difficult pharmacological approach. Asbestos exposure is very toxic for the lungs, which counteract this toxic effect by activating some antioxidant defense proteins. When these proteins are more active that in normal conditions, as in several cancers, these tumors become able to survive and resist to stress or chemotherapy. In our laboratory, we collected cellular samples of mesothelioma and non-transformed mesothelium from Hospital’s Biobank and we evaluated these proteins. Our results demonstrated these proteins are upregulated in mesothelioma cells and not in non-transformed mesothelium. This event could be associated to toxic effects evoked by asbestos exposure, highlighting the need in the future to monitor asbestos-exposed people by measuring biomarkers identified, in the attempt to identify them as possible predictive markers and potential pharmacological targets addressed to improve mesothelioma prognosis.

Abstract

Although asbestos has been banned in most countries around the world, malignant pleural mesothelioma (MPM) is a current problem. MPM is an aggressive tumor with a poor prognosis, so it is crucial to identify new markers in the preventive field. Asbestos exposure induces oxidative stress and its carcinogenesis has been linked to a strong oxidative damage, event counteracted by antioxidant systems at the pulmonary level. The present study has been focused on some redox-sensitive transcription factors that regulate cellular antioxidant defense and are overexpressed in many tumors, such as Nrf2 (Nuclear factor erythroid 2-related factor 2), Ref-1 (Redox effector factor 1), and FOXM1 (Forkhead box protein M1). The research was performed in human mesothelial and MPM cells. Our results have clearly demonstrated an overexpression of Nrf2, Ref-1, and FOXM1 in mesothelioma towards mesothelium, and a consequent activation of downstream genes controlled by these factors, which in turn regulates antioxidant defense. This event is mediated by oxidative free radicals produced when mesothelial cells are exposed to asbestos fibers. We observed an increased expression of Nrf2, Ref-1, and FOXM1 towards untreated cells, confirming asbestos as the mediator of oxidative stress evoked at the mesothelium level. These factors can therefore be considered predictive biomarkers of MPM and potential pharmacological targets in the treatment of this aggressive cancer.

Diagnostics in Pleural Disease

Pleural disease diagnostics represent a sprawling topic that has enjoyed a renaissance in recent years from humble beginnings. Whilst pleural patients are heterogeneous as a population and in the aetiology of the disease with which they present, we provide an overview of the typical diagnostic approach. Pleural fluid analysis is the cornerstone of the diagnostic pathway; however, it has many shortcomings. Strong cases have been made for more invasive upfront investigations, including image-guided biopsies or local anaesthetic thoracoscopy, in selected populations. Imaging can guide the diagnostic process as well as act as a vehicle to facilitate therapies, and this is never truer than with the recent advances in thoracic ultrasound.

The potential utility of GATA binding protein 3 for diagnosis of malignant pleural mesotheliomas

Malignant pleural mesothelioma is associated with asbestos exposure and poor outcomes. The usefulness of immunohistochemistry for diagnosis of sarcomatoid mesothelioma, especially the desmoplastic type, is limited, and more effective markers are required. GATA binding protein 3 (GATA3) has been suggested as a diagnostic marker for sarcomatoid mesothelioma. The potential usefulness of GATA3 for prognostication and its clinical and pathological correlations in different subtypes of mesothelioma have not been evaluated. We investigated the immunohistochemical labeling and associations for GATA3, BRCA1-associated protein 1 (BAP1), and Ki67 labeling in three major histological types of pleural malignant mesotheliomas. We examined 149 clinically annotated malignant mesotheliomas and assessed associations of GATA3 expression with clinical variables and prognosis. In addition, we labeled 10 cases of fibrous pleuritis with GATA3, all of which were negative. GATA3 was positive in 75 of 149 (50%) mesotheliomas, with the highest incidence of labeling seen in the sarcomatoid subtype (73%), compared with the biphasic (50%) and epithelioid (40%), mesotheliomas. A total of eight desmoplastic mesotheliomas showed labeling with GATA3. Patients whose tumors had sarcomatoid histology showed poorer survival than those with the other subtypes (p < 0.001), but overall GATA3 labeling did not have a statistically significant association with survival (p = 0.602). There was no association of GATA3 labeling and BAP1 status or Ki67 index. Our study includes the largest cohort of mesotheliomas that has been labeled for GATA3 to date. GATA3 is a useful marker for sarcomatoid mesothelioma, including the desmoplastic subtype. Discordance in GATA3 and BAP1 labeling of epithelioid and sarcomatoid components in the biphasic subtype is not uncommon.

The 2019 ERS/ESTS/EACTS/ESTRO Guidelines on the Management of Patients With Malignant Pleural Mesothelioma

Malignant pleural mesothelioma is a rare aggressive cancer, with insidious growth, and is associated with poor outcomes that have not improved over the years. A task force made up of members of the European Respiratory Society (ERS)/European Society of Thoracic Surgeons (ESTS)/European Association for Cardio-Thoracic Surgery (EACTS)/European Society for Radiotherapy and Oncology (ESTRO) societies, who are experts in the field of malignant mesothelioma, reviewed the literature from 2009 to 2018 to update the 2009 guidelines concerning epidemiology, diagnosis, staging, and treatment, including surgical, radiotherapy, and medical management, as well as palliative care to provide the best evidence-based recommendations for this patient population.

Benign multicystic peritoneal mesothelioma: literature review and update

Benign multicystic peritoneal mesothelioma (BMPM) is a rare peritoneal tumor diagnosed predominantly in pre-menopausal women. Associated risk factors include endometriosis and pelvic inflammatory disease in women, and prior abdominal surgery in both genders. To date, the pathogenesis of this disease remains controversial with possible etiologies, including a neoplastic versus a reactive process. Given the risk factors, some authors believe that this disease is secondary to a reactive process. However, because some studies describe cases where there is no prior surgical history or inflammatory milieu present, and because of this entity’s predilection for recurrence, some authors believe the origin to be neoplastic. Some genetic and familial associations have also been reported. Malignant transformation is extremely rare, with only two cases reported in the literature, despite the recurrence potential. Like the etiology, the name of this entity is also controversial. Some authors prefer the term “peritoneal inclusion cyst (PCM)” instead of “benign cystic mesothelioma” and argue that the term mesothelioma should only be used when there is evidence of atypia. Most cases of BMPM are discovered incidentally. Others reflect sequela of tumor mass effect. It appears intra-operatively as large, multi-focal, cystic lesions in the peritoneal and pelvic cavity. Diagnosis is achieved through surgical sampling with histopathological examination. Immunobiologically, BMPM exhibits multiple small cystic spaces with flattened lining containing calretinin positive cells without atypical features, mitotic figures, or tissue invasion. Treatment includes cytoreductive surgery. Here we present a case of BMPM in a 60-year-old male – a rare disease in an uncommon patient population.

Prognostic and clinicopathological utility of programmed death-ligand 1 in malignant pleural mesothelioma: A meta-analysis

OBJECTIVE

Programmed death ligand 1 (PD-L1) has been reported to be connected to prognosis in individuals with malignant pleural mesothelioma (MPM), although there is no consensus based on data from previous studies. Accordingly, this quantitative meta-analysis investigated prognostic and clinicopathological utility of PD-L1 in patients with MPM.

METHODS

A comprehensive search of the PubMed, Web of Science, Embase, and Cochrane Library databases for articles published up to October 4, 2019 was performed. Studies using immunohistochemical techniques to detect/quantify the expression of PD-L1 in MPM tissue were enrolled in the analysis. The combined hazard ratio (HR) and corresponding 95% confidence interval (CI) was applied to assess the association between PD-L1 expression and overall survival (OS).

RESULTS

A total of 11 studies comprising 1606 patients was included in the present meta-analysis. For OS, pooled data revealed an HR of 1.50 (95% CI 1.32-1.70; p < 0.001), suggesting that patients with PD-L1 overexpression experience inferior OS. Subgroup analysis revealed that elevated PD-L1 remained a significant prognostic indicator for worse OS, irrespective of sample size, cut-off value, ethnicity, and Newcastle-Ottawa Scale score. Moreover, PD-L1 overexpression was associated with non-epithelioid histology (odds ratio 4.30 [95% CI 1.89-9.74]; p < 0.001).

CONCLUSIONS

Results of this meta-analysis show that elevated expression of PD-L1 could be a factor predicting poorer survival in patients with MPM.

Current applications of molecular testing on body cavity fluids

INTRODUCTION

Effusion cytology has a high sensitivity for the diagnosis of malignancy and provides abundant material for molecular testing. Effusion draining is a minimally invasive procedure with few complications.

MATERIALS AND METHODS

We performed a review of publications regarding the use of molecular testing in serous effusions.

RESULTS

In diagnostics, BAP-1 IHC and CDKN2A FISH are powerful tools for the diagnosis of malignant mesothelioma. FISH, PCR, and EBER-ISH work well in lymphomas. RT-PCR may enhance the diagnosis of secondary epithelial malignancies. In theranostics, molecular testing on serous effusions is widely reported for the detection of alterations in genes related to lung carcinomas, such as EGFR, ALK, ROS1, and BRAF. PD-L1 expression testing by immunohistochemistry (IHC) also seems to be viable in this type of sample. HER2 FISH and IHC provide actionable results in the context of breast malignancies. Results in serous effusions seem to be equivalent to tissue biopsies for most applications and across different molecular techniques. The most interesting technology is next-generation sequencing (NGS), given its ability to sequence multiple genes on a single sample and the decreasing costs that have closely followed increasing throughputs. Cell-free DNA from effusion supernatants might be the most promising area for future research, showing superiority to serum and even to cell-block samples in limited studies.

CONCLUSIONS

Molecular tests are viable in serous effusion specimens when sufficient material is available. Given the rising importance of molecular testing we expect this to be an active field of research in the near future.

Differential Diagnosis of Malignant Pleural Mesothelioma on Cytology: A Gene Expression Panel versus BRCA1-Associated Protein 1 and p16 Tests

Pleural effusions are among the first clinical manifestations of malignant pleural mesothelioma (MPM) and often constitute the only available material for diagnosis. Although an MPM diagnosis can be reliable on cytology, the reported sensitivity is low (30% to 75%). Particularly, it can be hard to discriminate epithelioid MPM, the most common histotype, from reactive mesothelial hyperplasia (MH). Currently, BRCA1-associated protein 1 (BAP1) and CDKN2A (p16), evaluated by immunohistochemistry and fluorescent in situ hybridization, respectively, are the most valuable markers to discriminate MPM and MH. Both markers have a high specificity, but their sensitivity is not always satisfying, even when used together. We have recently developed a 117-gene expression panel, based on Nanostring technology, able to differentiate epithelioid MPM from MH pleural tissues better than BAP1 and p16. Herein, we evaluated the efficacy of the same panel on an independent retrospective cohort of 23 MPM and 11 MH pleural effusions (cell blocks and smears). The overall sensitivity and specificity of the panel were equal to 0.9565 and 1, respectively. Moreover, the panel performance was compared with BAP1 and p16 on 25 cell blocks. Sensitivity levels of gene panel, BAP1 alone, p16 alone, and BAP1 plus p16 were 1, 0.5882, 0.4706, and 0.7647, respectively. Specificity was always 1. Although further validation is needed, this gene panel could really facilitate patients' management, allowing a definitive MPM diagnosis directly on pleural effusions.

Guidelines for the cytopathologic diagnosis of epithelioid and mixed-type malignant mesothelioma: Complementary statement from the international mesothelioma interest group, also endorsed by the international academy of cytology and the papanicolaou society of cytopathology. A proposal to be applauded and promoted but which requires updating

The guidelines for the cytopathologic diagnosis of epithelioid and mixed-type malignant mesothelioma produced by the International Mesothelioma Interest Group and which are endorsed by the International Academy of Cytology and the Papanicolaou Society of Cytopathology are reviewed and discussed. This (predominantly) evidence-based document provides a robust and useful framework for diagnosticians and guideline producers to emphasise and promote the value, power and role of cytology in mesothelioma diagnosis and management with comments and suggestions about how the guidelines can be updated and improved in the future.

A gene-expression-based test can outperform bap1 and p16 analyses in the differential diagnosis of pleural mesothelial proliferations

The demonstration of tissue invasion by histology is an essential criterion for the differential diagnosis of benign and malignant mesothelial proliferations. When tissue invasion cannot be identified, the use of ancillary tests is sometimes necessary. Among investigated markers, the loss of BRCA1 associated protein 1 (BAP1) protein expression and the homozygous deletion of p16 have shown 100% specificity in separating benign and malignant mesothelial lesions. However, beyond the excellent specificity of these two markers, their low sensitivity limits their clinical utility. In this context, a previous study developed and tested a novel tool for use in the differential diagnosis of malignant pleural mesothelioma (MPM) using the NanoString System and a classification algorithm. In the current study, the performance of gene classifiers were compared using BAP1 and p16 testing. p16 FISH and BAP1 immunohistochemistry were performed on the same series of 34 epithelioid MPM and 20 benign pleural lesions, which were previously analyzed by the system. The diagnostic performance of p16, BAP1 and our classification models were compared using ROC analysis. It was observed that BAP1 loss and p16 deletion were highly specific for MPM, since they were not detected in benign lesions. However, their AUC values were not completely satisfying (BAP1: 0.8235; p16: 0.7647) particularly due to their low sensitivities. As expected, combining BAP1 and p16 tests increased the diagnostic sensitivity, thus improving the AUC (0.8824). In the same series of cases, our MPM tool outperformed BAP1 and p16 tests using the 22 and 40-gene classification models (AUC 22-gene model: 0.9996; AUC 40-gene model: 0.9990). In conclusion, the present gene-expression-based classification exhibited great potential and further validation is required to support these findings in a prospective fashion, in order to provide a solid alternative for pleural proliferation diagnosis.

Proceedings of the American Society of Cytopathology companion session at the 2019 United States and Canadian Academy of Pathology Annual meeting, part 2: effusion cytology with focus on theranostics and diagnosis of malignant mesothelioma

We live in the "era" of minimally invasive procedures, molecular testing, and personalized care. Effusions have a high sensitivity and will often yield diagnostic cytological material. The companion session presented by the American Society of Cytopathology at the 2019 United States and Canadian Academy of Pathology meeting outlined our current and future projected practices in characterizing, managing, and diagnosing serous cavity fluids. In this second part, the role of theranostics and the diagnosis of malignant mesothelioma, as was discussed at the meeting, have been highlighted. In theranostics, a vast amount of data has been reported regarding the epidermal growth factor receptor and related molecules. Some studies have also reported on HER2 immunohistochemistry and fluorescence in situ hybridization. This follows the most active areas of research in targeted therapy. Furthermore, during this session, malignant mesothelioma was extensively discussed. The cytologic diagnosis of malignant mesothelioma in effusion specimens has been controversial; however, a definitive diagnosis will be possible in many cases. Radiologic information should be sought, because the radiologist can often provide a definite or very likely diagnosis of malignancy. Microscopically, high cellularity and/or numerous balls of cells or papillary groups will favor the diagnosis of mesothelioma. It is important to exclude metastatic carcinoma with a broad-spectrum carcinoma marker, of which claudin-4 has been the best, because it will not cross react with mesothelioma. BAP1 and MTAP immunohistochemistry and CDKN2A fluorescence in situ hybridization are very useful adjunctive techniques for separating benign from malignant mesothelial proliferations. The use of 2 of these approaches together will produce a sensitivity of 80% to 90% for epithelial mesotheliomas in the pleura, although the sensitivity has been lower in the peritoneal cavity.

Malignant Pleural Effusion and Its Current Management: A Review

Malignant pleural effusion (MPE) is an exudative effusion with malignant cells. MPE is a common symptom and accompanying manifestation of metastatic disease. It affects up to 15% of all patients with cancer and is the most common in lung, breast cancer, lymphoma, gynecological malignancies and malignant mesothelioma. In the last year, many studies were performed focusing on the pathophysiological mechanisms of MPE. With the advancement in molecular techniques, the importance of tumor-host cell interactions is becoming more apparent. Additionally, the process of pathogenesis is greatly affected by activating mutations of EGFR, KRAS, PIK3CA, BRAF, MET, EML4/ALK and RET, which correlate with an increased incidence of MPE. Considering all these changes, the authors aim to present a literature review of the newest findings, review of the guidelines and pathophysiological novelties in this field. Review of the just recently, after seven years published, practice guidelines, as well as analysis of more than 70 articles from the Pubmed, Medline databases that were almost exclusively published in indexed journals in the last few years, have relevance and contribute to the better understanding of the presented topic. MPE still presents a severe medical condition in patients with advanced malignancy. Recent findings in the field of pathophysiological mechanisms of MPE emphasize the role of molecular factors and mutations in the dynamics of the disease and its prognosis. Treatment guidelines offer a patient-centric approach with the use of new scoring systems, an out of hospital approach and ultrasound. The current guidelines address multiple areas of interest bring novelties in the form of validated prediction tools and can, based on evidence, improve patient outcomes. However, the role of biomarkers in a clinical setting, possible new treatment modalities and certain specific situations still present a challenge for new research.

Identification of mesothelioma-specific sialylated epitope recognized with monoclonal antibody SKM9-2 in a mucin-like membrane protein HEG1

The anti-mesothelioma mAb SKM9-2 recognizes the sialylated protein HEG homolog 1 (HEG1). HEG1 is a 400 kDa mucin-like membrane protein found on mesothelioma. SKM9-2 can detect mesothelioma more specifically and sensitively than other antibodies against current mesothelioma markers; therefore, SKM9-2 would be likely useful for the precise detection and diagnosis of malignant mesothelioma. In the present study, we investigated the epitope of SKM9-2. We analyzed the binding of SKM9-2 to truncated HEG1 and candidate epitope-fused glycosylphosphatidylinositol-anchor proteins. The epitope of SKM9-2 was identified as an O-glycosylated region, 893-SKSPSLVSLPT-903, in HEG1. An alanine scanning assay of the epitope showed that SKM9-2 bound to a simple epitope in HEG1, and the SKxPSxVS sequence within the epitope was essential for SKM9-2 recognition. Mass spectrometry analysis and lectin binding analysis of soluble epitope peptides indicated that the SKM9-2 epitope, in which Ser⁸⁹⁷ was not glycosylated, contained two disialylated core 1 O-linked glycan-modified serine residues, Ser⁸⁹³ and Ser⁹⁰⁰. Neuraminidase treatment analysis also confirmed that the epitope in mesothelioma cells contained a similar glycan modification. The specific detection of mesothelioma with SKM9-2 can thus be performed by the recognition of sialylated glycan modification in the specific region of HEG1.

How to assess the best immunohistochemical panel in the diagnosis of malignant pleural mesothelioma in a pathology lab

BACKGROUND

malignant pleural mesothelioma (MPM) is a rare tumor with a challenging diagnosis. Even if, clinical data are mandatory to suspect the diagnosis, the positive diagnosis is based on microscopic features. Morphologic features are still the port of call of the diagnosis but their non specific character and the multiplicity of differential diagnoses made the immunohistochemical markers mandatory for the diagnosis. Many antibodies with a positive diagnostic value including claretinin, mesothelin, WT1 and antibodies with a negative diagnostic value including TTF1, EMA, CD15 are recommended by the scientific societies. This is due to the diagnostic limits of every antibody which necessitate the association of multiple antibodies. In the diagnostic demarch, pathologists deal with different antibodies and clones. Even if many recommendations are available, every pathology lab has to experiment its own antibodies in order to optimize the routine diagnostic demarch especially in low-income country. Our aim was to assess the diagnostic value of different antibodies available in our lab and to recommend a decisional flowchart.

PATIENTS AND METHODS

we conducted a retrospective study about 30 MPM diagnosed over a 20-year-period. The different techniques were realized manually. The different antibodies used were anti-calretinin, anti-Epithelial Membrane Antigen (EMA), anti-mesothelin, anti-Thyroid Transcription Factor 1 (TTF1), anti-ACE, anti-cytokeratin, anti-vimentin, anti-CD15, anti-cytokeratin 5/6, anti-bcl2, and anti-CD99 and anti-CD34 antibodies. The sensitivity and specificity of these antibodies were assessed.

RESULTS

the microscopic exam concluded to an epithelioid mesothelioma (EM) in 17 cases, sarcomatoid mesothelioma (SM) in four cases and biphasic mesothelioma (BM) in nine cases. The immunohistochemical study was performed in all cases. A mean of eight antibodies was used in every case, average 4 to 20 antibodies. The immunohistochemical study was repeated from 2 to 5 times in 15 cases and concerned a mean of 3 antibodies per case. In EM and BM, the antibodies with positive predictive value and highest sensitivity were calretinin, EMA, cytokeratin, and vimentin reaching respectively a sensitivity of 86.2%, 89.7%, 92.9% and 89.3%. The most valuable antibodies with negative predictive value were TTF1, CD15 and ACE that presented a specificity reaching respectively 100%. In sarcomatoid mesothelima, the most sensitive antibody was the cytokeratin antibody.

CONCLUSION

these results yielded to a diagnostic flowchart that we can use in routine practice and that is in accordance with the literature findings. Many diagnostic and technical pitfalls have to be known by pathologists when dealing with MPM.