Guidelines for Pathologic Diagnosis of Mesothelioma: 2023 Update of the Consensus Statement From the International Mesothelioma Interest Group

CONTEXT.—

Mesothelioma is an uncommon tumor that can be difficult to diagnose.

OBJECTIVE.—

To provide updated, practical guidelines for the pathologic diagnosis of mesothelioma.

DATA SOURCES.—

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

CONCLUSIONS.—

There was consensus opinion regarding guidelines for (1) histomorphologic diagnosis of mesothelial tumors, including distinction of epithelioid, biphasic, and sarcomatoid mesothelioma; recognition of morphologic variants and patterns; and recognition of common morphologic pitfalls; (2) molecular pathogenesis of mesothelioma; (3) application of immunohistochemical markers to establish mesothelial lineage and distinguish mesothelioma from common morphologic differentials; (4) application of ancillary studies to distinguish benign from malignant mesothelial proliferations, including BAP1 and MTAP immunostains; novel immunomarkers such as Merlin and p53; fluorescence in situ hybridization (FISH) for homozygous deletion of CDKN2A; and novel molecular assays; (5) practical recommendations for routine reporting of mesothelioma, including grading epithelioid mesothelioma and other prognostic parameters; (6) diagnosis of mesothelioma in situ; (7) cytologic diagnosis of mesothelioma, including use of immunostains and molecular assays; and (8) features of nonmalignant peritoneal mesothelial lesions.

Pulmonary Cytopathology: Current and Future Impact of Microscopy and Immunohistochemistry

With the advancement of tissue procurement techniques, in-depth knowledge of morphology is crucial for cytopathologists to diagnose neoplastic and nonneoplastic lung diseases optimally. Cytopathologists must also be well versed in immunohistochemistry/immunocytochemistry markers and their interpretation for an accurate diagnosis.

Combined detection of SHOX2 and PTGER4 methylation with serum marker CYFRA21-1 for improved diagnosis of malignant pleural mesothelioma

AIMS

To investigate the performance of a combined biomarker approach using the methylation status of the short stature homeobox 2 (SHOX2) and prostaglandin E2 receptor EP4 (PTGER4) genes, along with the serum levels of CYFRA21-1, for differential diganosis of malignant pleural mesothelioma (MPM) from benign reactive mesothelial hyperplasia (RMH).

METHODS

We analysed 48 MPM tissue or pleural effusion cell block specimens and 42 cases with RMH. Real-time quantitative methylation-specific PCR was used to examine the methylation status of SHOX2, PTGER4, ras association domain family 1 isoform A, septin 9 gene and homeobox gene A9 genes. Additionally, we employed electrochemiluminescence immunoassay to measure nine serum tumour markers commonly used in pan-cancer screening tests.

RESULTS

The receiver operating curve indicated that SHOX2, PTGER4 gene methylation and serum biomarker CYFRA21-1 exhibited good diagnostic performance in identifying MPM, with area under curves (AUCs) of 0.761, 0.904 and 0.847, respectively. The combination of SHOX2, PTGER4 methylation and CYFRA21-1 yielded an AUC value of 0.972. The diagnostic sensitivity and specificity of this panel in differentiating MPM from RMH were 91.3% (42/46) and 97.6% (41/42), respectively. Both tissue and cell block specimens can be used in the diagnostic process. Furthermore, elevated CYFRA21-1 levels were associated with poor prognosis (p<0.05). Hypermethylation level of PTGER4 may indicate an unfavourable prognosis of MPM, but the difference was not statistically significant.

CONCLUSIONS

The combined detection of SHOX2 and PTGER4 methylation alongside serum CYFRA21-1 level significantly enhances the diagnosis of MPM. Additionally, CYFRA21-1 can serve as a prognostic indicator for MPM.

Case Report: Primary malignant mesothelioma of the left atrium easily misdiagnosed as myxoma

Background

Malignant mesothelioma (MM) is a rare and aggressive tumor that is found in the pleura and peritoneum. A few cases of MM in the pericardium and tunica vaginalis testis have been reported. Moreover, primary occurrence in the atrium is extremely rare. The visual appearance of this tumor is similar to that of a common atrial myxoma, which makes it challenging for clinicians and radiologists to diagnose and treat this disease.

Case demonstration

An 18-year-old woman presented with symptoms of chest pain, shortness of breath, cough, and expectoration for 7 days. Echocardiography was performed on the patient, which revealed an atrial mass. Myxoma was one of the differential diagnoses. The tumor was an elliptical mass with tips, and the cut surface was jelly-like, similar to myxoma. After surgery, a pathologic examination of the biopsied tumor confirmed epithelial-type MM. During postoperative follow-up, no recurrence of the tumor was observed.

Conclusions

MM originating in the atrium is considered to be extremely rare. Consequently, clinicians can easily misdiagnose atrial MM as a myxoma. Moreover, to confirm the diagnosis, histopathologic biopsy, histomorphological characterization, immunohistochemistry, and molecular genetic testing are required. Therefore, clinical diagnosis and treatment of MM are challenging.

Diagnostic performance of immunohistochemistry markers for malignant pleural mesothelioma diagnosis and subtypes. A systematic review and meta-analysis

BACKGROUND

Malignant pleural mesothelioma (MPM) poses diagnostic challenges due to its resemblance to benign pleural pathologies and different histological subtypes. Several immunohistochemistry markers have been employed to aid in accurate diagnosis.

METHODS

The present systematic review and meta-analysis aimed to assess the diagnostic performance of various immunohistochemistry markers in malignant pleural mesothelioma diagnosis and its histological subtypes. Following the PRISMA guidelines, we systematically searched the literature for articles on using different immunohistochemical markers in MPM and its histological subtypes. EMBASE, LILACS, MEDLINE, and Virtual Health Library were searched for studies published up to August 2023. We used the QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies) criteria to assess the quality of the included articles. Meta-analyses were performed to determine prevalence using a random-effects model.

RESULTS

103 studies met the inclusion criteria, comprising a diverse range of immunohistochemistry markers. EMA and desmin-loss exhibited high sensitivity (96% and 92%, respectively) in distinguishing malignant pleural mesothelioma from benign pleural pathologies. Specificity was notably high for both BAP1-loss and survivin expression at 100%. Subtype-specific analyses demonstrated that EMA and HEG1 were sensitive markers for epithelioid mesothelioma, while GLUT1 showed high sensitivity for sarcomatoid mesothelioma. In cases comparing epithelioid mesothelioma and lung adenocarcinoma, CAM5.2 and calretinin displayed high sensitivity, while WT1 and BAP1-loss demonstrated exceptional specificity for malignant epithelioid mesothelioma. In the case of sarcomatoid mesothelioma and sarcomatoid lung carcinoma, GATA3 exhibited the most heightened sensitivity, while GATA3 and D2-40 displayed the best specificity for sarcomatoid malignant mesothelioma diagnosis.

CONCLUSION

Immunohistochemistry markers are essential in accurately diagnosing malignant pleural mesothelioma and its histological subtypes. This systematic review and meta-analysis provide a comprehensive insight into the diagnostic performance of these markers, facilitating their potential clinical utility in the discrimination of malignant pleural mesothelioma from other pleural pathologies and the differentiation of malignant pleural mesothelioma subtypes.

Investigation of MTAP and BAP1 staining loss and P16/CDKN2A deletion in pleural cytology specimens and its role in the diagnosis of mesothelioma

BACKGROUND

Mesothelioma is a malignant neoplasm with a poor survival rate. We aimed to investigate the importance of BAP1, MTAP (IHC), and p16/CDKN2A homozygous deletion (FISH) in cytologic material obtained from pleural effusion sampling, which is a less invasive procedure in the diagnosis of mesothelioma.

METHODS

Our study discussed pleural cytology samples of cases with histopathologically proven mesothelioma diagnoses between 2017 and 2022. As the control group, materials that had pleural effusion sampling for other reasons and reactive mesothelial hyperplasia were included in the study. Cell blocks prepared from these materials were subjected to fluorescent in situ hybridization for p16/CDKN2A homozygous deletion and immunohistochemistry for BAP1 and MTAP.

RESULTS

The specificity of the P16/CDKN2A homozygous deletion in diagnosing mesothelioma is 100%. Its sensitivity is 68.75%. The specificity of BAP1 immunohistochemical nuclear expression loss is 95%, while the sensitivity is 60%. Loss of nuclear expression of MTAP alone has the lowest specificity and sensitivity, with a specificity of 86% and a sensitivity of 43%. The highest sensitivity is reached when BAP1 loss and p16/CDKN2A homozygous deletion are evaluated together, increasing to 81%. The specificity is 95%.

CONCLUSION

It has been determined that any marker alone cannot be used for a definitive mesothelioma diagnosis in pleural effusion cytological specimens; however, sensitivity increases in some combinations. The combination of BAP1 immunohistochemistry and p16/CDKN2A homozygous deletion detected by FISH, which has a higher specificity and sensitivity, can be routinely used in the diagnosis of mesothelioma under the guidance of clinical and radiologic information.

An Updated Contextual Approach to Mesothelial Proliferations in Pleural Effusion Cytology Leveraging Morphology, Ancillary Studies, and Novel Biomarkers

CONTEXT.—

Pleural effusions are common cytologic specimens that can be leveraged to make diagnoses of malignancy that drive appropriate patient management. However, the overlap in morphologic features of reactive mesothelial proliferations, mesotheliomas, and adenocarcinomas can create diagnostic pitfalls in the cytologic evaluation of pleural fluids.

OBJECTIVE.—

To review the morphologic spectrum of benign and malignant mesothelial proliferations in pleural effusions, as well as relevant clinicoradiologic contexts and ancillary tests.

DATA SOURCES.—

Existing scientific and clinical literature as of January 2023.

CONCLUSIONS.—

We can leverage the knowledge of several overlapping morphologic features, clinicoradiologic scenarios, and immunohistochemical studies to enhance the diagnostic accuracy of pleural effusion cytology to appropriately delineate cases of adenocarcinoma, reactive mesothelial proliferation, and mesothelioma. Earlier diagnosis through cytology, particularly in cases of mesothelioma, may positively impact patient treatment options and prognosis.

Mesothelioma in the pleura, pericardium and peritoneum: Recommendations from the International Collaboration on Cancer Reporting (ICCR)

AIMS

Mesothelioma is a rare malignancy of the serosal membranes that is commonly related to exposure to asbestos. Despite extensive research and clinical trials, prognosis to date remains poor. Consistent, comprehensive and reproducible pathology reporting form the basis of all future interventions for an individual patient, but also ensures that meaningful data are collected to identify predictive and prognostic markers.

METHODS AND RESULTS

This article details the International Collaboration on Cancer Reporting (ICCR) process and the development of the international consensus mesothelioma reporting data set. It describes the 'core' and 'non-core' elements to be included in pathology reports for mesothelioma of all sites, inclusive of clinical, macroscopic, microscopic and ancillary testing considerations. An international expert panel consisting of pathologists and a medical oncologist produced a set of data items for biopsy and resection specimens based on a critical review and discussion of current evidence, and in light of the changes in the 2021 WHO Classification of Tumours. The commentary focuses particularly upon new entities such as mesothelioma in situ and provides background on relevant and essential ancillary testing as well as implementation of the new requirement for tumour grading.

CONCLUSION

We recommend widespread and consistent implementation of this data set, which will facilitate accurate reporting and enhance the consistency of data collection, improve the comparison of epidemiological data, support retrospective research and ultimately help to improve clinical outcomes. To this end, all data sets are freely available worldwide on the ICCR website (www.iccr-cancer.org/data-sets).

Neurofibromatosis Type 2-Yes-Associated Protein and Transcriptional Coactivator With PDZ-Binding Motif Dual Immunohistochemistry Is a Reliable Marker for the Detection of Neurofibromatosis Type 2 Alterations in Diffuse Pleural Mesothelioma

Neurofibromatosis type 2 (NF2) loss occurs in approximately 30% to 50% of diffuse pleural mesothelioma (DPM) with accumulation of yes-associated protein (YAP) 1 and transcriptional coactivator with PDZ-binding motif (TAZ) in tumor nuclei. NF2 and YAP/TAZ represent potential therapeutic targets. We investigated the performance of NF2-YAP/TAZ dual immunohistochemistry (IHC) in identifying DPM that harbors NF2 alterations and in distinguishing DPM from benign mesothelial proliferations. NF2-YAP/TAZ IHC was subsequently performed in a Discovery cohort of DPMs with (n = 10) or without (n = 10) NF2 alterations detected by next-generation sequencing (NGS) and 9 benign cases. The cutoff values for loss of NF2 expression and YAP/TAZ overexpression using IHC were determined in the Discovery cohort. The performance characteristics of NF2-YAP/TAZ IHC were investigated in a Validation cohort (20 DPMs and 10 benign cases). In the Discovery cohort, all DPMs with NF2 alterations using NGS showed NF2 IHC scores of <2, whereas all NF2-wild-type DPMs showed scores of ≥2. NF2-altered DPMs had significantly higher YAP/TAZ H-scores (P < .001) than NF2-wild-type DPM and benign pleura (median H-scores: 237.5 [range, 185-275], 130.0 [range, 40-225], and 10.0 [range, 0-75], respectively). NF2-YAP/TAZ IHC demonstrated 95.2% sensitivity, 100% specificity, 100% positive predictive value, and 95% negative predictive value for detecting NF2 alterations in DPM (n = 40) with NGS as the gold standard and 87.5% sensitivity and 100% specificity for distinguishing DPM (n = 40) from benign mesothelial proliferations (n = 19). NF2-YAP/TAZ IHC has a high sensitivity and specificity for detecting NF2 alterations in DPM and a high specificity for malignancy, highlighting potential utility for guiding NF2-targeted therapies and distinguishing DPM from benign mimics.

The cytologic diagnosis of mesothelioma: are we there yet?

INTRODUCTION

Mesothelioma is a rare but highly aggressive malignancy with poor prognosis that frequently present with recurrent effusions. Establishing the diagnosis by cytology can lead to early diagnosis and treatment and consequently improve prognosis.

MATERIALS AND METHODS

This review examines the cytological diagnosis of mesothelioma in the context of its historical and morphologic evolution and provides an update of the current reporting systems. Clues to identify the mesothelial and malignant nature of the sample are detailed as well as the supporting ancillary tests.

RESULTS

Cytologically, the samples are overwhelmingly cellular and malignancy is recognized by both architectural and cytological atypia. Numerous variably sized clusters and enlarged cells are easily identified, some with papillary architecture and collagen cores. Recognizing the mesothelial nature of the cells and supportive immunostains are essential to rule out the differential diagnosis of metastatic carcinomas and reactive mesothelium. Current ancillary tests such as homozygous deletion of CDKN2A, loss of BRCA1-associated protein, and methylthioadenosine phosphorylase expression can provide further support of malignancy.

CONCLUSIONS

At this time with the aid of current ancillary tests and in the hands of cytopathologists with adequate experience with the interpretation of effusions, the diagnosis of mesothelioma can be established with accuracy in most cases.

Benefits and Challenges of Inhibiting EZH2 in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive thoracic cancer that is mainly associated with prior exposure to asbestos fibers. Despite being a rare cancer, its global rate is increasing and the prognosis remains extremely poor. Over the last two decades, despite the constant research of new therapeutic options, the combination chemotherapy with cisplatin and pemetrexed has remained the only first-line therapy for MPM. The recent approval of immune checkpoint blockade (ICB)-based immunotherapy has opened new promising avenues of research. However, MPM is still a fatal cancer with no effective treatments. Enhancer of zeste homolog 2 (EZH2) is a histone methyl transferase that exerts pro-oncogenic and immunomodulatory activities in a variety of tumors. Accordingly, a growing number of studies indicate that EZH2 is also an oncogenic driver in MPM, but its effects on tumor microenvironments are still largely unexplored. This review describes the state-of-the-art of EZH2 in MPM biology and discusses its potential use both as a diagnostic and therapeutic target. We highlight current gaps of knowledge, the filling of which will likely favor the entry of EZH2 inhibitors within the treatment options for MPM patients.

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.

Malignant peritoneal mesothelioma with massive ascites as the first symptom: A case report

BACKGROUND

Malignant peritoneal mesothelioma (MPM) is an extremely rare tumor with nonspecific clinical manifestations, which is extremely difficult to diagnose. Herein, we reported a case of MPM in the abdominal cavity with massive short-term ascites as the first symptom.

CASE SUMMARY

A 65-year-old woman presented to the hospital with abdominal pain, distention, and shortness of breath that persisted for 15 d. The serum CA-125 level was 1075 U/mL. The abdominal computed tomography showed massive ascites and no obvious tumor lesions. The pathological examination of the ascitic fluid showed numerous heterotypic cells with some papillary structures. The immunohistochemistry and fluorescence in situ hybridization showed the deletion of CDX2 (-), WT-1 (-), Ki-67 (about 10% +), CEA (-), Glut-1 (+++), desmin (-), PD-L1 (-), and CDKN2A (P16). The final diagnosis was MPM. The patient refused tumor cytoreductive surgery and received two cycles of cisplatin plus pemetrexed bidirectional chemotherapy. In the second cycle, she received an additional cycle of hyperthermic intraperitoneal chemotherapy and immune checkpoint inhibitor therapy due to massive recalcitrant ascites. She died of disease progression 2 mo after diagnosis.

CONCLUSION

In case of massive unexplained ascites, the possibility of MPM should not be excluded to avoid misdiagnosis and delay in treatment.

Clinical and molecular validation of BAP1, MTAP, P53, and Merlin immunohistochemistry in diagnosis of pleural mesothelioma

BAP1 and MTAP immunostains play an important role in diagnosis of mesothelioma, but additional markers are needed to increase sensitivity. We analyzed 84 pleural mesotheliomas (51 epithelioid, 27 biphasic, 6 sarcomatoid) by a hybrid-capture next-generation sequencing (NGS) panel including complete coverage of coding and splicing regions for BAP1, CDKN2A/MTAP, NF2, and TP53 and correlated molecular findings with diagnostic immunostains for BAP1, MTAP, Merlin, and p53, respectively. Fifty-seven reactive mesothelial proliferations served as benign comparators. Loss of BAP1, MTAP, and Merlin protein expression were, respectively, 54%, 46%, and 52% sensitive and 100% specific for mesothelioma. Two-marker immunopanels of BAP1 + MTAP, BAP1 + Merlin, and MTAP + Merlin were 79%, 85%, and 71% sensitive for mesothelioma, while a three-marker immunopanel of BAP1 + MTAP + Merlin was 90% sensitive. Diffuse (mutant-pattern) p53 immunostaining was seen in only 6 (7%) tumors but represented the only immunohistochemical abnormality in 2 cases. Null-pattern p53 was not specific for malignancy. An immunopanel of BAP1 + MTAP + Merlin + p53 was 93% sensitive for mesothelioma, and panel NGS detected a pathogenic alteration in BAP1, MTAP, NF2, and/or TP53 in 95%. Together, 83 (99%) of 84 tumors showed a diagnostic alteration by either immunohistochemistry or panel NGS. Adding Merlin to the standard BAP1 + MTAP immunopanel increases sensitivity for mesothelioma without sacrificing specificity. p53 immunohistochemistry and panel NGS with complete coverage of BAP1, CDKN2A/MTAP, TP53, and NF2 may be useful in diagnostically challenging cases.

A Community-Driven, Openly Accessible Molecular Pathway Integrating Knowledge on Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a highly aggressive malignancy mainly triggered by exposure to asbestos and characterized by complex biology. A significant body of knowledge has been generated over the decades by the research community which has improved our understanding of the disease toward prevention, diagnostic opportunities and new treatments. Omics technologies are opening for additional levels of information and hypotheses. Given the growing complexity and technological spread of biological knowledge in MPM, there is an increasing need for an integrating tool that may allow scientists to access the information and analyze data in a simple and interactive way. We envisioned that a platform to capture this widespread and fast-growing body of knowledge in a machine-readable and simple visual format together with tools for automated large-scale data analysis could be an important support for the work of the general scientist in MPM and for the community to share, critically discuss, distribute and eventually advance scientific results. Toward this goal, with the support of experts in the field and informed by existing literature, we have developed the first version of a molecular pathway model of MPM in the biological pathway database WikiPathways. This provides a visual and interactive overview of interactions and connections between the most central genes, proteins and molecular pathways known to be involved or altered in MPM. Currently, 455 unique genes and 247 interactions are included, derived after stringent manual curation of an initial 39 literature references. The pathway model provides a directly employable research tool with links to common databases and repositories for the exploration and the analysis of omics data. The resource is publicly available in the WikiPathways database (Wikipathways : WP5087) and continues to be under development and curation by the community, enabling the scientists in MPM to actively participate in the prioritization of shared biological knowledge.

Analysis of early pleural fluid samples in patients with mesothelioma: A case series exploration of morphology, BAP1, and CDKN2A status with implications for the concept of mesothelioma in situ in cytology

BACKGROUND

The concept of mesothelioma in situ has been revisited and is a new World Health Organization diagnostic entity. The definition centers on ancillary techniques used in pleural mesothelioma (PM) assessment. At the authors' institution, most PM diagnoses are made on cytologic specimens. Effusion samples obtained before definitive PM diagnosis were interrogated using BRCA1-associated protein 1 gene (BAP1), cyclin-dependent kinase inhibitor 2A gene (CDKN2A) and cytologic evaluation to assess whether early or possible in situ disease could be characterized.

METHODS

All cases of PM diagnosed between January 2008 and December 2019 were identified at a tertiary referral center. Patients who had a pleural fluid sample collected 24 months before the diagnosis were selected, numbering 8 in total. The cytomorphology of each sample was reviewed; and, retrospectively, BAP1 immunohistochemistry (IHC) and CDKN2A fluorescence in situ hybridization (FISH) were performed on initial and diagnostic samples.

RESULTS

The initial samples were deemed benign in 5 cases and atypical mesothelial proliferations in 3 cases. A spectrum of apparently normal to atypical cytomorphologic changes was identified. BAP1 loss was present in 6 of 8 initial cases, whereas CDKN2A homozygous deletion was identified in 1 of 7 initial cases. Either abnormality was identified in 7 of 8 initial samples.

CONCLUSIONS

Detectable abnormalities of BAP1 IHC and CDKN2A FISH were present in pleural fluid specimens before the development of cytomorphologic features diagnostic of PM. This is the largest series to date describing cytology samples early in the course of PM development, thereby highlighting a possible cytological equivalent for mesothelioma in situ.

Cytological diagnosis of malignant mesothelioma: A case series

Background:

Mesotheliomas are neoplasms of the serosal lining of the body cavities. Diagnosis requires a multimodal approach of clinical findings, cytology, and histopathology with immunohistochemistry (IHC). The published sensitivity of cytology for diagnosing mesothelioma ranges from 30% to 75%.

Aim and Objectives:

This study aimed to calculate the incidence of malignant mesothelioma (MM) at our institute and to study the cytological features of MM.

Materials and Methods:

A retrospective study of pleural, peritoneal, and pericardial fluids submitted at our institute was done. The duration of the study was 8 years (2011–2019). Apart from examining Giemsa smears, a panel of immunocytochemical (ICC) and cell block immunohistochemical (IHC) markers was applied to achieve the diagnosis. These included calretinin, mesothelin, CK5/6, Hector Battifora mesothelial cell antibody (HBME), WT1, MOC31, CK7 and CK20. Histopathological correlation was done wherever possible.

Result:

In the present study, we compiled four cases of MM over 8 years diagnosed on serous effusion cytology and confirmed by immunocytochemistry (ICC)/cell block immunohistochemistry (IHC)/biopsy. This indicates a rare incidence of MM. The Cytological features of MM were studied.

Conclusion:

The diagnosis of MM is difficult, especially cytologically. It was found to be a rare entity in the malignant cases diagnosed on effusion cytology.

Evidence-based diagnostic performance of novel biomarkers for the diagnosis of malignant mesothelioma in effusion cytology

Cytology effusions are often the only material available for diagnosing malignant pleural mesothelioma (MPM). However, the cytomorphological features alone are not always diagnostic, and cytology samples preclude an assessment for pleural tissue invasion. Accordingly, immunohistochemical, soluble, and molecular biomarkers have been developed. The aim of this study is to provide quantitative evidence regarding the diagnostic performance of novel biomarkers. To that end, a systematic literature review was performed of articles dealing with a loss of BRCA1-associated protein 1 (BAP1), methylthioadenosine (MTAP), 5-hydroxymethylcitosine (5-hmC), glucose transporter 1 (GLUT1), insulin like-growth factor II messenger RNA-binding protein 3 (IMP3), enhanced zeste homologue 2 (EZH2) staining, cyclin-dependent kinase inhibitor 2A (CDKN2A) homozygous deletion (HD) testing, soluble mesothelin, and microRNA quantification in cytological samples for the diagnosis of MPM versus reactive atypical mesothelial cells. Sensitivity and specificity were extracted, and a meta-analysis was performed. The quality of the studies was assessed with Quality Assessment of Diagnostic Accuracy Studies 2, and the quality of the evidence was evaluated with the Grading of Recommendations Assessment, Development, and Evaluation approach. Seventy-one studies were included. BAP1 loss showed a sensitivity of 0.65 (confidence interval [CI], 0.59-0.71) and a specificity of 0.99 (CI, 0.93-1.00). MTAP loss and p16 HD showed 100% specificity with sensitivities of 0.47 (CI, 0.38-0.57) and 0.62 (CI, 0.53-0.71), respectively. BAP1 loss and CDKN2A HD combined showed maximal specificity and a sensitivity of 0.83 (CI, 0.78-0.89). GLUT1 and IMP3 showed sensitivities of 0.82 (CI, 0.70-0.90) and 0.65 (CI, 0.41-0.90), respectively, with comparable specificity. Mesothelin showed a sensitivity of 0.73 (CI, 0.68-0.77) and a specificity of 0.90 (CI, 0.84-0.93). In conclusion, some of the recently emerging biomarkers are close to 1.00 specificity. Their moderate sensitivity on their own, however, can be significantly improved by the use of 2 biomarkers, such as a combination of BAP1 and CDKN2A with fluorescence in situ hybridization or a combination of BAP1 and MTAP immunohistochemistry.

Molecular cytology of the respiratory tract and pleura

There is growing evidence that molecular testing is feasible on all types of cytological preparation, which is fortunate as more diagnostic markers and biomarkers for targeted therapies are discovered for use in pulmonary and pleural malignancies. In this article we will discuss the pre-analytic, analytic, and post-analytic (interpretive) considerations for successful implementation of molecular tests for diagnostic and predictive markers in respiratory and pleural cytology. The vast majority of laboratories are familiar with, and have validated their molecular protocols for, formalin-fixed paraffin-embedded surgical specimens, which are not directly applicable to cytology specimens. Thus, rigorous validation must be performed for each type of fixative and cytology preparation before it is implemented in the clinical setting.

Ancillary Diagnostic Investigations in Malignant Pleural Mesothelioma

For a number of patients presenting with an undiagnosed pleural effusion, frailty, medical co-morbidity or personal choice may preclude the use of pleural biopsy, the gold standard investigation for diagnosis of malignant pleural mesothelioma (MPM). In this review article, we outline the most recent evidence on ancillary diagnostic tests which may be used to support a diagnosis of MPM where histological samples cannot be obtained or where results are non-diagnostic. Immunocytochemical markers, molecular techniques, diagnostic biomarkers and imaging techniques are discussed. No adjunctive test has a sensitivity and specificity profile to support use in isolation; however, correlation of pleural fluid cytology with relevant radiology and supplementary biomarkers can enable an MDT-consensus clinico-radiological-cytological diagnosis to be made where further invasive tests are not possible or not appropriate. Diagnostic challenges surrounding non-epithelioid MPM are recognised, and there is a critical need for reliable and non-invasive investigative tools in this population.

[Adenomatoid tumor of the adrenal gland: Clinicopathologic characteristics and differential diagnosis on two tumors of exceptional adrenal location]

Adenomatoid tumors are benign tumors from mesothelial origin, usually occurring in the genital tract. Extragenital locations, especially in the adrenal gland are extremely rare. Here we are reporting two cases of a 28-year-old and 50-year-old men with an adenomatoid tumor of the right adrenal gland. Usual morphological aspects join scattered and microcystic pattern with epithelioid or signet-ring cells. According to the morphological features, main differential diagnoses are adenocarcinoma metastasis, vascular tumors or mesotheliomas. Immunohistochemistry provides precious help to confirm the mesothelial origin thanks to positivity of epithelial markers (CK7, AE1-AE3, CK5/6) coupled to mesothelial markers (D2-40, Calretinin, WT1). On the other hand, there is no loss of BAP1 by immunohistochemistry and usually a surexpression of P16. Adrenal gland adenomatoid tumor is a benign tumor, which can be promoted by iatrogenous or constitutive immunodepression.

Diagnostic utility of BAP1 for malignant pleural mesothelioma in pleural fluid specimens with atypical morphology

OBJECTIVE

To assess the utility of BRCA1-associated protein 1 (BAP1) immunohistochemistry (IHC) for the diagnosis of malignant pleural mesothelioma (MPM) in fluid samples with atypical cytology.

METHODS

Pleural fluid samples with an atypical mesothelial proliferation (diagnostic categories: 'atypical' and 'suspicious') received between January 2015 and March 2018 at a tertiary referral centre were identified. Results of routine IHC testing were recorded for each case. BAP1 by IHC was performed and a final diagnosis sought from subsequent pathology specimens, medical records, or consensus clinical diagnosis.

RESULTS

Of 50 cases identified, 41 were reported as atypical and 9 as suspicious. Seven (14%) demonstrated loss of BAP1 staining, 40 retained BAP1 staining, 1 had heterogeneous staining, and 2 had insufficient cells for analysis. All seven cases with BAP1 loss were diagnosed with MPM on follow-up. Of those with retained BAP1, 52.5% (21) were subsequently diagnosed with MPM, while 40% (16) had non-MPM diagnoses after a median follow-up of 24 months. Three cases were not further investigated based on patient and clinician decision. The case with heterogeneous staining was diagnosed as mesothelioma by clinical consensus.

CONCLUSIONS

BAP1 IHC loss is highly specific for malignancy and has value as a rule-in test. Even in a tertiary centre with clinical interest in the cytological diagnosis of MPM this investigation was able to increase diagnostic accuracy beyond routine IHC studies. Cytological criteria remain valuable, as retained BAP1 in an atypical or suspicious mesothelial proliferation cannot exclude malignancy.

Diagnostic Utility of BAP1, EZH2 and Survivin in Differentiating Pleural Epithelioid Mesothelioma and Reactive Mesothelial Hyperplasia: Immunohistochemical Study

Background: Epithelioid mesothelioma (EM) is the commonest subtype of malignant pleural mesothelioma. Its histopathological discrimination from reactive mesothelial hyperplasia (RMH) could be challenging. Thus, an immunohistochemical panel is mandatory for better discrimination. BAP1 is a newly identified diagnostic marker whose loss is specific to malignant mesothelioma. EZH2 overexpression is reported in different cancers, but its relation to BAP1 in malignant mesothelioma has not been fully understood. Survivin expression is said to be significantly higher in EM than in non-neoplastic pleural tissue, but its diagnostic utility as an immunohistochemical marker has not been thoroughly investigated in this field. To the best of our knowledge, no previous studies have been conducted to assess the diagnostic accuracy of the combined use of these three nuclear markers (BAP1, EZH2 and Survivin) in discriminating pleural EM from RMH. Methods: This retrospective study includes two groups: 81 cases of pleural EM and 67 cases of RMH, retrieved from the archives of Pathology Department of Ain Shams University Hospitals and Ain-Shams University Specialized Hospital during the period from January 2016 to December 2019. An immunohistochemical study was performed using BAP1, EZH2 and Survivin antibodies. Results: There were highly statistically significant relations between study groups as regards the studied markers (p = 0.001 for each). The specificity was 100% for all combinations of immunohistochemical markers. Sensitivity of any combination of the immunohistochemical markers used in this study was found to be higher than the sensitivity of any of these markers used individually. The combination of all three markers showed the highest diagnostic accuracy (95.9%) and the highest sensitivity (92.6%). However, the combination of Survivin and EZH2 yielded the same diagnostic accuracy and sensitivity. Conclusion: Adding EZH2, Survivin and BAP1 to the diagnostic IHC panel for differentiating pleural EM and RMH could enhance diagnostic sensitivity. Moreover, Survivin is a potentially promising marker in this context, especially when combined with EZH2.

Clinicopathological characteristics of primary peritoneal epithelioid mesothelioma of clear cell type: A case report

RATIONALE

Primary peritoneal epithelioid mesothelioma of clear cell type is an extremely rare entity composed of clear cytoplasm. It is challenging to diagnose because of the morphological resemblance to clear cell tumor.

PATIENTS CONCERNS

A 69-year-old male patient had swollen lymph nodes in the right inguinal region for 7 months and was constipated for 1 month.

DIAGNOSIS

The patient was diagnosed as peritoneal epithelioid mesothelioma of clear cell type based on computed tomography scan, pathology, immunohistochemistry, special staining and whole-exome sequencing. This patient harbored VHL gene alteration in exon 1 and homologous recombination defect (with a score of 45). This finding indicated that this patient might be sensitive to platinum-based therapy and Poly ADP-ribose Polymerase (PARP) inhibitor. This patient carried no microsatellite instability, a low level of tumor mutation burden, and a high extent of intratumoral heterogeneity. Eighteen neoantigens were detected.

INTERVENTIONS

The patient received surgery-based multidisciplinary treatment by integrating cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC). HIPEC was administered with docetaxel 120 mg plus cisplatin 120 mg, at 43°C, for 60 minutes. After operation, the patient received intravenous (IV) chemotherapy with docetaxel 60 mg, pemetrexed 750 mg and cisplatin 100 mg, and then intraperitoneal (IP) chemotherapy with docetaxel 40 mg. The patient received interventional therapy of hepatic artery embolization for 5 times.

OUTCOMES

Regular follow-up was performed until Oct 14, 2020. The patient died 31.6 months later owing to incomplete intestinal obstruction.

LESSONS

Primary peritoneal epithelioid mesothelioma of clear cell type needs to be differentiated from a variety of clear cell tumors. This disease is characterized by specific genetic alteration. Whole-exome sequencing contributes to guide individualized therapy. CRS-HIPEC helps achieve long-term overall survival.

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.

Fluorescence in situ hybridization detection of chromosome 22 monosomy in pleural effusion cytology for the diagnosis of mesothelioma

BACKGROUND

Malignant pleural mesothelioma (MPM) is characterized by mutations in several genes, including cyclin-dependent kinase-inhibitor 2A/p16 in the 9p21 locus, BRCA1-associated protein 1 (BAP1), and neurofibromatosis type 2 (NF2) in the 22q12 locus. Recent studies indicate that fluorescence in situ hybridization (FISH) detects hemizygous loss of NF2 in tissue specimens of MPM. The authors investigated whether NF2 FISH, either alone or in combination with other diagnostic assays (9p21 FISH, methylthioadenosine phosphorylase [MTAP] immunohistochemistry [IHC], and BAP1 IHC), effectively distinguishes MPM cells from reactive mesothelial cells (RMCs) in cell blocks prepared from pleural effusions.

METHODS

FISH assays were used to examine the deletion status of NF2 and 9p21, and IHC was used to determine the expression of MTAP and BAP1 in cell blocks from 54 cases with MPM and 18 cases with RMCs.

RESULTS

Hemizygous NF2 loss (chromosome 22 monosomy or hemizygous deletion) showed 51.9% sensitivity (48.1% for chromosome 22 monosomy and 3.7% for hemizygous deletion) and 100% specificity in differentiating MPM cells from RMCs. Combinations of NF2 FISH, 9p21 FISH, and BAP1 IHC assays yielded greater sensitivity (98.1%) than any assay alone (9p21 FISH, 61.1%; MTAP IHC, 52.8%; or BAP1 IHC, 60.4%). The level of hemizygous NF2 loss in cell blocks positively correlated with that in corresponding tissues. Furthermore, to overcome cytologic specimen-specific challenges, FISH combined with cytokeratin AE1/AE3 immunofluorescence was necessary in 25.9% of MPM cases for FISH assessment of predominantly scattered MPM cells.

CONCLUSIONS

NF2 FISH alone or in combination with other diagnostic assays effectively differentiates MPM cells from RMCs in cell blocks prepared from pleural effusions.

Diagnostic mesothelioma biomarkers in effusion cytology

Malignant mesothelioma is a rare malignancy with a poor prognosis whose development is related to asbestos fiber exposure. An increasing role of genetic predisposition has been recognized recently. Pleural biopsy is the gold standard for diagnosis, in which the identification of pleural invasion by atypical mesothelial cell is a major criterion. Pleural effusion is usually the first sign of disease; therefore, a cytological specimen is often the initial or the only specimen available for diagnosis. Given that reactive mesothelial cells may show marked atypia, the diagnosis of mesothelioma on cytomorphology alone is challenging. Accordingly, cell block preparation is encouraged, as it permits immunohistochemical staining. Traditional markers of mesothelioma such as glucose transporter 1 (GLUT1) and insulin-like growth factor 2 mRNA-binding protein 3 (IMP3) are informative, but difficult to interpret when reactive proliferations aberrantly stain positive. BRCA1-associated protein 1 (BAP1) nuclear staining loss is highly specific for mesothelioma, but sensitivity is low in sarcomatoid tumors. Cyclin-dependent kinase inhibitor 2A (CDKN2A)/p16 homozygous deletion, assessed by fluorescence in situ hybridization, is more specific for mesothelioma with better sensitivity, even in the sarcomatoid variant. The surrogate marker methylthioadenosine phosphorylase (MTAP) has been found to demonstrate excellent diagnostic correlation with p16. The purpose of this review is to provide an essential appraisal of the literature regarding the diagnostic value of many of these emerging biomarkers for malignant mesothelioma in effusion cytology.

Histopathological and immunohistochemical features of 14 peritoneal mesotheliomas with clinical outcomes and recent updates

Background

Malignant peritoneal mesotheliomas (MPMs) are rare tumors with overlapping clinical and histopathological features, especially with epithelial ovarian carcinomas (EOCs). There is no substantial documentation on these rare tumors from our country.

Objective

To study the clinicopathological features including immunohistochemical (IHC) profile and clinical outcomes of 14 MPMs, diagnosed at our institution.

Materials and Methods

This was a retrospective study, wherein 14 cases of MPM, occurring in female patients, diagnosed at our institution, between January 2008 and May 2019 were included, after a critical review.

Results

Median age was 54.5 years. Most patients presented with ascites, omental nodularity, and fat stranding. Microscopically, most cases (11, 78.6%) displayed epithelioid morphology, followed by biphasic pattern (2, 14.3%) and a single case of well-differentiated MPM. IHC, diagnostic sensitivity and specificity of calretinin were 100% (13/13) and 85.7%; of HBME1 were 100% (5/5) and 100%; and of podoplanin (D2-40) were 60% (2/5) and 100%. Other positively expressed immunomarkers were epithelial membrane antigen (n = 2/5, 40%), cytokeratin 5/6 (n = 4/4, 100%), and WT1 (n = 9/10, 90%). Most patients (5/12, 41.7%) were treated with chemotherapy. The 3-year disease-free and overall survival rates were 25.7% and 54%, respectively, including improved survival trend in patients with epithelioid type of MPMs.

Conclusion

MPMs are diagnosed with a combination of clinicopathological features and optimal IHC markers. Their differentiation from EOCs and other metastatic carcinomas is imperative in view of significant treatment implications.

The Separation of Benign and Malignant Mesothelial Proliferations: New Markers and How to Use Them

The separation of benign from malignant mesothelial proliferations is an important clinical but often a difficult morphologic problem. Over the last roughly 10 years a variety of new markers that aid in this separation have been published and some older recommended markers reconsidered. Unlike previous, and largely unusable, empiric immunohistochemical (IHC) stains, these new markers, some using IHC and some using fluourescent in situ hybridization (FISH), are largely based on documented genomic abnormalities in malignant mesotheliomas. However, no marker works in all situations; rather, markers need to be chosen by the morphology of the process in question (epithelial vs. spindled) and the body cavity of interest (pleural vs. peritoneal). It is also important to be familiar with the exact pattern, for example nuclear versus cytoplasmic loss, that indicates a positive test. Furthermore, no single marker is 100% sensitive even with the optimal morphology/location, so that combinations of markers are essential. This review covers the various new markers in the literature, highlights their advantages and limitations, and suggests morphology/site specific combinations that can produce sensitivities in the 80% to 90% (and perhaps higher) range. At present only BRCA-1 related protein-1 and methylthioadenosine phosphorylase IHC, and cyclin-dependent kinase inhibitor 2A (p16) FISH have sufficient publications and reproducibility of results to be considered as established markers. 5-Hydroxymethyl cytosine, enhancer of zeste homolog 2, cyclin D1, and programmed death-ligand 1 IHC, and NF2 FISH are all potentially useful but need further study. The newly described entity of malignant mesothelioma in situ sits at the interface of benign and malignant mesothelial process; criteria for this diagnosis are reviewed.

Root cause analysis of indeterminate diagnoses in serous fluids cytopathology

INTRODUCTION

The International System for Reporting Serous Fluid Cytopathology proposed five diagnostic categories: Nondiagnostic (ND), Negative for Malignancy (NFM), Atypia of Undetermined Significance (AUS), Suspicious for Malignancy (SFM) and Malignant (MAL) (Primary or Metastatic). The indeterminate (AUS/SFM) categories are challenging for management. The goal of this study is to reveal the root causes contributing to indeterminate diagnoses (ID).

MATERIALS AND METHODS

We searched our archives between 1 January 2017 and 30 June 2019, and performed a root cause analysis (RCA) using the "5 whys" method to determine the contributing factors of ID.

RESULTS

Nine hundred eleven specimens were evaluated and diagnosed: ND (9, 1%), NFM (667, 73.2%), AUS (51, 5.6%), SFM (27, 3%) and MAL (157, 17.2%). More than one factor contributed to 38/78 ID. Low volume (<50 cc), and low cellularity were identified in 31 and 51 cases, respectively. Three cases were simply deferred to concurrent biopsy. Eleven cases were called atypical, favor reactive mesothelium despite confirmatory IHC. Atypical lymphoid population was reported in seven cases. Cellblocks (CB) were low in cellularity despite volume >1000 mL in 13 cases. Two mesotheliomas were underdiagnosed as suspicious.

CONCLUSIONS

Low cellularity and low volume were the most common contributing factors, highlighting the importance of adequate sample collection. Adequate volume specimens with low cellularity may benefit from a close inspection and a second CB. Some IDs can be switched to NFM or MAL with careful consideration of clinical, radiologic findings and ancillary testing, and concurrent surgical pathology correlation when available.

Development of mesothelioma in situ and its progression to invasive disease observed in a patient with uncontrolled pleural effusions for 15 years

Mesothelioma in situ (MIS) has recently been investigated as a distinct phase of mesothelioma carcinogenesis. The diagnostic criteria proposed for MIS include a loss of BRCA1-associated protein 1 (BAP1) expression detected by immunohistochemistry (IHC). However, the length of time that MIS typically remains an in situ lesion before progression to invasive disease is still unclear. Herein, we report a case of a Japanese woman in her early seventies who had suffered from recurrent pleural effusions for 15 years, during which MIS developed and progressed to invasive mesothelioma. Retrospective diagnosis of partial MIS, fully developed MIS, and invasive disease was made using BAP1 IHC on three biopsy specimens and via clinical observations with radiological images. MIS and invasive lesions revealed BAP1 loss. The interval from partial or full MIS to invasive disease was 14 and 7 years, respectively. These results support a diagnostic strategy combining histomorphology with genomic-based assays including BAP1 IHC in biopsy tissues from a patient with recurrent pleural effusions.

The Use of Immunohistochemistry, Fluorescence in situ Hybridization, and Emerging Epigenetic Markers in the Diagnosis of Malignant Pleural Mesothelioma (MPM): A Review

Malignant pleural mesothelioma (MPM) is an aggressive asbestos related disease that is generally considered to be difficult to diagnose, stage and treat. The diagnostic process is continuing to evolve and requires highly skilled pathology input, and generally an extensive list of biomarkers for definitive diagnosis. Diagnosis of MPM requires histological evidence of invasion by malignant mesothelial cells often confirmed by various immunohistochemical biomarkers in order to separate it from pleural metastatic carcinoma. Often when invasion of neoplastic mesothelial cells into adjacent tissue is not apparent, further immunohistochemical testing - namely BAP1 and MTAP, as well as FISH testing for loss of p16 (CDKN2A) are used to separate reactive mesothelial proliferation due to benign processes, from MPM. Various combinations of these markers, such as BAP1 and/or MTAP immunohistochemistry alongside FISH testing for loss of p16, have shown excellent sensitivity and specificity in the diagnosis of MPM. Additionally, over the recent years, research into epigenetic marker use in the diagnosis of MPM has gained momentum. Although still in their research stages, various markers in DNA methylation, long non-coding RNA, micro RNA, circular RNA, and histone modifications have all been found to support diagnosis of MPM with generally good sensitivity and specificity. Many of these studies are however, limited by small sample sizes or other study limitations and further research into the area would be beneficial. Epigenetic markers show promise for use in the future to facilitate the diagnosis of MPM.

Reactive mesothelial hyperplasia mimicking mesothelioma in an African green monkey (Chlorocebus aethiops)

A spontaneous reactive mesothelial hyperplasia occurred in a female, 15.7-year-old African green monkey (grivet; Chlorocebus aethiops). At necropsy, massive effusions were found in the abdomen, the thorax, and the pericardium. Additionally, multiple small, beige-gray nodules were detected on the serosal surfaces of the abdominal organs. Histopathologically, the mesothelial cells resembled the epithelioid subtype of a mesothelioma, but no infiltrative or invasive growth could be demonstrated. The mesothelial cells on the thoracis, liver, and intestinal serosa were accompanied by chronic serositis. Mesothelial cells expressed cytokeratin, vimentin, calretinin, desmin, Wilms Tumor 1 (WT-1) protein, and epithelial membrane antigen (EMA). Cells were negative for carcinoembryonic antigen (CEA), cluster of differentiation 15 (CD15), and podoplanin. Ultrastructurally, cells revealed a moderate amount of microvilli of medium length, perinuclear tonofilament bundles, and long desmosomes. In fluorescence in situ hybridization (FISH) for the detection of characteristic gene loss (p16; CDKN2A), NF2, and MTAP, no deletions were detected. No asbestos fibers and no presence of Simian virus 40 antigen (SV40) could be demonstrated.

Genomic-based ancillary assays offer improved diagnostic yield of effusion cytology with potential challenges in malignant pleural mesothelioma

BRCA1-associated protein 1 (BAP1) or methylthioadenosine phosphorylase (MTAP) immunohistochemistry (IHC) or 9p21 fluorescence in situ hybridization (FISH) are useful for the diagnosis of malignant pleural mesothelioma (MPM). However, the effect of these assays on the diagnostic yield of effusion cytology in MPM cases with suspicious cytomorphology or the diagnostic challenges in BAP1 or MTAP IHC have not been fully elucidated. Two cohorts of cytologic preparations obtained from pleural effusions were examined: MPM cases in cohort 1 were used to evaluate whether BAP1 or MTAP IHC or 9p21 FISH increase the diagnostic yield of effusion cytology; cohort 2 included cases suspicious for MPM, to which BAP1 or MTAP IHC was applied to clarify the challenges in the clinical assessment of these assays. In cohort 1 (n = 28), either assay elevated 62.5% of class II or III cases to class V. In cohort 2 (n = 139), 21.7% of BAP1 immunocytochemistry in smears and 10.6% of BAP1 IHC and 9.4% of MTAP IHC in cell blocks, were identified to be challenging. The application of genomic-based assays increased the diagnostic yield of effusion cytology in the diagnosis of MPM. However, diagnostic challenges limit the application of these assays in some cases.

Clinical significance of histologic subtyping of malignant pleural mesothelioma

Malignant mesothelioma (MM) is uncommon, but very aggressive tumor arising from the mesothelial cells of pleura, pericardium, peritoneum, and tunica vaginalis. Despite multimodality treatments 5-year survival is only 5% after the diagnosis. Histology and TNM staging system are still the best prognostic factors. Furthermore, histologic subtype of MM determines the clinical management of the patients. According to the 2015 WHO classification, MM is divided into diffuse, localized and well differentiated papillary mesothelioma. Major histologic subtypes of diffuse MM, namely epithelioid, biphasic and sarcomatoid, have different prognosis. However, in the last decade it has become evident that more detailed subclassification and histologic/cytological characterization of MM have prognostic and perhaps predictive implications. In this review, major histologic subtypes and cytological features of MM are presented and their relation with prognosis and predictive biomarkers is discussed.

Multicystic and diffuse malignant peritoneal mesothelioma in children

BACKGROUND

Malignant and multicystic peritoneal mesotheliomas are extremely rare tumors in children, developing from mesothelial cells. No specific guidelines are available at this age.

METHODS

We performed a retrospective analysis of all identified children (< 18-year-old) treated in France from 1987 to 2017 for a diffuse malignant peritoneal mesothelioma (DMPM) or a multicystic peritoneal mesothelioma (MCPM).

RESULTS

Fourteen patients (5 males and nine females), aged 2.2 to 17.5 years, were included. The most frequent presenting symptoms were abdominal pain, ascitis, and alteration in the general condition. Eight patients had epithelioid mesothelioma, three had biphasic mesothelioma, and three had MCPM. Eight patients with DMPM diagnosis received cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC). Among them, six patients had neoadjuvant systemic chemotherapy, one patient, post-operative chemotherapy, and one patient CRS and HIPEC only. Three patients received only systemic chemotherapy. All patients with MCPM had only surgery. After a median follow-up of seven years (2-15), six patients (6/11; one death) with DMPM and two patients (two/three) with MCPM had a local and distant recurrences.

CONCLUSION

Peritoneal mesothelioma in children is a rare condition with difficult diagnosis and high risk of recurrence. Worldwide interdisciplinary collaboration and networking are mandatory to help diagnosis and provide harmonious treatment guidelines.

Integrative approach to cytologic and molecular diagnosis of malignant pleural mesothelioma

The global incidence of malignant mesothelioma (MM) causes considerable disease burden, suffering and health care costs. Beside preventive measures and ban the use of asbestos, early diagnosis would largely improve the chance of curative treatment. Current histologic criteria, however, requiring presence of invasion in the surrounding fatty tissue fail to identify MM in sufficiently early stage. Unilateral accumulation of pleural effusion is one of the earliest clinical manifestations of MM that occurs in approximately 90% of the patients. Therapeutic thoracocenthesis is necessary to remove the fluid and to relieve patients’ symptoms. This effusion is easily accessible and offers early and minimally invasive diagnosis by combining cytology with immunologic, molecular- and biomarker analyses. Typically, the fluid is rich in malignant cells and cell groups, but incipient stages of the disease may be difficult to recognize as the malignant cells can be masked by presence of inflammatory or reactive mesothelial cells. Recurrent, hemorrhagic and cell rich effusion should always be suspicious for MM and adequately prepared and analyzed to provide necessary information for subsequent therapy. Importantly, early detection of MM by integrating cytology and molecular approaches has high sensitivity and positive predictive value and has a major impact on patient survival. Thus, a conclusive positive MM cytology should lead to treatment without delay. This review summarizes molecular and diagnostic criteria of MM diagnosis.

Clinical long-term outcome of non-specific pleuritis (NSP) after surgical or medical thoracoscopy

Background

Thoracoscopy, either “medical” or “surgical”, is the gold standard to reveal the cause of pleural effusion by taking large biopsies. However, in some cases, the histology of pleural biopsies is inconclusive for a specific cause, describing a variable process of inflammation, encompassing for non-specific pleuritis (NSP). Questions are raised whether the surgical (or video-assisted thoracoscopic surgery, VATS) is doing better than the medical thoracoscopy (MT or pleuroscopy), but no direct comparison between the two techniques exist in the current bibliography. The aim of our retrospective study was to compare these two techniques to find whether there is any difference in the false negative cases of NSP.

Methods

We included in our study 295 patients with NSP, 179 patients who underwent VATS comparing to 116 patients who underwent MT for pleural effusion of initially undetermined cause, having a follow-up of at least one year. Analysis of patients’ files, history, clinical examinations, further tests, and follow-up were recorded.

Results

The mean age of our patients was 58.5±19.1 and M/F gender was 216/79; no difference was observed between the two groups. The mean follow-up period was 47.3±20.7 months. After VATS, only one patient (0.55%) was finally diagnosed with pleural malignancy (false negative) while after MT 2 patients (1.7%). Negative predictive value for pleura-related malignancy for VATS was 0.994 and for MT 0.982.

Conclusions

In patients with histological diagnosis of NSP both VATS and MT showed similar and excellent results of false negative cases and negative predictive value in excluding malignant pleural disease.

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.

Hemizygous loss of NF2 detected by fluorescence in situ hybridization is useful for the diagnosis of malignant pleural mesothelioma

Neurofibromatosis type 2 (NF2) gene, a tumor suppressor gene located on chromosome 22q12.2, is frequently abnormal in mesothelioma. Recent studies have revealed the effectiveness of diagnostic assays for differentiating malignant pleural mesothelioma from reactive mesothelial hyperplasia. These include detection of homozygous deletion of the 9p21 locus by fluorescence in situ hybridization (FISH) (9p21 FISH), loss of expression of BAP1 as detected by immunohistochemistry, and loss of expression of methylthioadenosine phosphorylase (MTAP) as detected by immunohistochemistry. However, the application of FISH detection of NF2 gene deletion (NF2 FISH) in differentiation of malignant pleural mesothelioma from reactive mesothelial hyperplasia has not been fully evaluated. In this study, we investigated whether NF2 FISH, either alone or in a combination with other diagnostic assays (9p21 FISH, MTAP immunohistochemistry, and BAP1 immunohistochemistry), is effective for distinguishing malignant pleural mesothelioma from reactive mesothelial hyperplasia. This study cohort included malignant pleural mesothelioma (n = 47) and reactive mesothelial hyperplasia cases (n = 27) from a period between 2001 and 2017. We used FISH to examine deletion status of NF2 and 9p21 and immunohistochemistry to examine expression of MTAP and BAP1 in malignant pleural mesothelioma and in reactive mesothelial hyperplasia. Hemizygous NF2 loss (chromosome 22 monosomy or hemizygous deletion) was detected in 25 of 47 (53.2%) mesothelioma cases. None of the mesothelioma cases showed homozygous NF2 deletion. Hemizygous NF2 loss showed 53.2% sensitivity and 100% specificity in differentiating malignant pleural mesothelioma from reactive mesothelial hyperplasia. A combination of NF2 FISH, 9p21 FISH, and BAP1 immunohistochemistry yielded greater sensitivity (100%) than that detected for either diagnostic assay alone (53.2% for NF2 FISH, 78.7% for 9p21 FISH, 70.2% for MTAP immunohistochemistry, or 57.4% for BAP1 immunohistochemistry). Thus, NF2 FISH in combination with other diagnostic assays is effective for distinguishing malignant pleural mesothelioma from reactive mesothelial hyperplasia.

Application of immunohistochemistry in diagnosis and management of malignant mesothelioma

Immunohistochemistry plays an indispensable role in accurate diagnosis of malignant mesothelioma, particularly in morphologically challenging cases and in biopsy and cytology specimens, where tumor architecture is difficult or impossible to evaluate. Application of a targeted panel of mesothelial- and epithelial-specific markers permits correct identification of tumor lineage in the vast majority of cases. An immunopanel including two mesothelial markers (calretinin, CK5/6, WT-1, or D2-40) and two epithelial markers (MOC-31 and claudin-4) offers good sensitivity and specificity, with adjustments as appropriate for the differential diagnosis. Once mesothelial lineage is established, malignancy-specific studies can help verify a diagnosis of malignant mesothelioma. BAP1 loss, CDKN2A homozygous deletion, and MTAP loss are highly specific markers of malignancy in a mesothelial lesion, and they attain acceptable diagnostic sensitivity when applied as a diagnostic panel. Novel markers of malignancy, such as 5-hmC loss and increased EZH2 expression, are promising, but have not yet achieved widespread clinical adoption. Some diagnostic markers also have prognostic significance, and PD-L1 immunohistochemistry may predict tumor response to immunotherapy. Application and interpretation of these immnuomarkers should always be guided by clinical history, radiographic findings, and above all histomorphology.

Interobserver variation in the assessment of the sarcomatoid and transitional components in biphasic mesotheliomas

The percentage of sarcomatoid component has an impact on prognosis in patients with biphasic malignant pleural mesothelioma. Recent study showed that the transitional pattern similar to sarcomatoid component of malignant mesothelioma has negative prognostic significance. Practice guidelines recommend quantification of sarcomatoid component despite poor diagnostic reproducibility of biphasic mesothelioma among thoracic pathologists. The aim of this study was to determine the interobserver agreement in the quantification of sarcomatoid component, and in the diagnosis of a transitional component in the biphasic malignant mesothelioma. Thirteen experts in thoracic pathology reviewed the representative H&E and cytokeratin whole-slide images of the 54 biphasic mesotheliomas, without knowledge of BAP1 or p16 deletion status, and completed the survey of 25 questions. The overall interobserver agreement in the assessment of the percentage of the sarcomatoid component in 25% increments was good (wK = 0.62). Excellent agreement was present in 14 of 54 cases (26%), and 3 cases were unanimously scored. Excellent agreement was reached for the cases with 0-24% and > 75% of the sarcomatoid component.The most commonly used criteria for the diagnosis of sarcomatoid component were malignant spindle cells, frank sarcomatoid features and high N/C ratio. The overall interobserver agreement for transitional pattern was fair (wK = 0.40). Unanimous opinion about the absence of transitional pattern was observed in only one case. At least 70% agreement regarding the presence of transitional pattern was observed in 12 cases, with the rest of the cases showing a wide range of disagreement. Morphologic characteristics that favor transitional pattern over non-transitional include sheet-like growth of cohesive, plump, elongated epithelioid cells with well-defined cell borders and a tendency to transition into spindle cells. Our study defined precise morphologic criteria that may be used in the differential diagnosis between transitional pattern and other mesothelioma subtypes including sarcomatoid and epithelioid.

Cyclin D1 immunohistochemical staining to separate benign from malignant mesothelial proliferations

The separation of benign from malignant mesothelial proliferations is a morphologically difficult problem. Mutations/deletions of components of the Hippo pathway are frequent in malignant mesotheliomas, and one downstream effect of aberrant Hippo signaling is increased production of cyclin D1. We examined expression of cyclin D1 nuclear staining in two tissue microarrays containing 52 reactive epithelial mesothelial proliferations, 51 reactive spindle cell mesothelial proliferations, 54 epithelial mesotheliomas, and 22 sarcomatous/desmoplastic mesotheliomas. When present, cyclin D1 staining was always strong, hence the arrays were scored as 0, 1-25%, 26-50%, 51-75%, and 76-100% staining. Both arrays showed a similar pattern. Reactive epithelial proliferations generally showed no staining (42/52 cases) or 1-25% staining (10/52 cases) with no cases showing >25% staining. Overall for reactive epithelial proliferations the maximum staining was 14.8% and mean 1.1 ± 2.9%. For epithelial mesotheliomas 39/54 (72%) cases demonstrated >25% staining, with 8/54 in the 26-50% staining range, 9/54 in the 51-75% range, and 22/54 in the >75% range. Combinations of staining using cyclin D1 >50% plus BAP1 or MTAP loss in epithelial mesotheliomas produced about a 10% increase in sensitivity. Reactive spindle cell proliferations showed a broader range of staining with 27/51 in the 1-25% range, 5/51 in the 26-50% range, and 1/51 >50%. Eleven of 22 sarcomatous/desmoplastic mesotheliomas scored 50% or greater. We conclude that for epithelial mesothelial proliferations, the finding of >50% of tumor cells staining supports a diagnosis of epithelial mesothelioma with 100% specificity but only modest (57%) sensitivity.

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.