Reactive Mesothelial Proliferations Research Articles

Diagnostic Utility of Cell block and Immunocytochemistry in Differentiating Malignant from Non-malignant Effusions: A Cross-sectional Study

Introduction: Cytological evaluation of body cavity fluids has been widely employed in diagnosing the underlying aetiology. Differentiating reactive mesothelial cell proliferations from metastatic malignant cells based on cytomorphology alone is challenging. Therefore, the use of cell blocks in conjunction with immunocytochemistry can significantly improve diagnostic accuracy. Aim: To investigate the role of cell blocks and immunocytochemistry in distinguishing malignant from non- malignant effusion fluids. Materials and Methods: A prospective cross-sectional study was conducted on 70 serous effusion fluid samples (ascitic and pleural fluids) received in the Cytology section of the Pathology Department from October 2021 to November 2022. Relevant clinical details, including demographic information, age, gender, presenting complaints, and radiological and laboratory investigations, were documented from the patients’ medical records. All fluids underwent conventional cytology, and the remaining fluid was used for cell block preparations. Immunocytochemistry was performed using Ber-EP4 and Calretinin immuno-markers to differentiate between reactive mesothelial cells and malignant cells. The association between cytosmear/cell block and immunocytochemistry was calculated using the chi-square test. Results: Out of the 70 cases, 44 were pleural fluids, and 26 were ascitic fluids. Conventional cytology identified 11 positive cases, 20 suspicious cases, and 39 negative cases for malignancy. However, after cell block examination, the total number of positive cases reduced to 9, suspicious cases decreased to 12, and negative cases increased to 49, resulting in a 14.3% increase in diagnostic accuracy. Immunocytochemistry using Ber-EP4 showed strong positivity in 12 cases, indicating epithelial malignancy (adenocarcinoma), while 9 cases were Ber-EP4 negative. Calretinin positivity was observed in the mesothelial cells of all 21 cases where immunohistochemistry was performed, resulting in a 17.5% increase in diagnostic accuracy. Conclusion: The combination of cell block technique with conventional cytology improves the diagnostic yield and accuracy by providing better interpretation of architectural patterns and cytomorphology. Additionally, the application of immunocytochemistry using Ber-EP4 and Calretinin aids in distinguishing malignant from non-malignant serous effusions.

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

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. To review the morphologic spectrum of benign and malignant mesothelial proliferations in pleural effusions, as well as relevant clinicoradiologic contexts and ancillary tests. Existing scientific and clinical literature as of January 2023. 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.

CDKN2A/p16 evaluation in cytology specimens.

CDKN2A/p16 evaluation in cytology specimens.

Utility of BAP1, p16, and Methylthio-Adenosine Phosphorylase Immunohistochemistry in Cytological and Histological Samples of Pleural Mesotheliomas

Introduction: In most cases, the diagnostic workup of pleural mesotheliomas (MPMs) starts with cytological examination of pleural effusion, but histology is needed to confirm the diagnosis. The introduction of BAP1 and methylthio-adenosine phosphorylase (MTAP) immunohistochemistry has become a powerful tool to confirm the malignant nature of mesothelial proliferations also in cytological specimens. The objective of this study was to determine the concordance of BAP1, MTAP, and p16 expression between cytological and histological samples of patients with MPM. Methods: Immunohistochemistry of BAP1, MTAP, and p16 was performed on cytological samples and compared with the corresponding histological specimen of 25 patients with MPM. Inflammatory and stromal cells served as positive internal control for all three markers. In addition, samples of 11 patients with reactive mesothelial proliferations served as an external control group. Results: Loss of BAP1, MTAP, and p16 expression was found in 68%, 72%, and 92% of MPM, respectively. Loss of MTAP was associated with loss of p16 expression in all cases. Concordance of BAP1 between cytological and corresponding histological samples was 100% (kappa coefficient 1; p = 0.008). For MTAP and p16, kappa coefficient was 0.9 (p = 0.01) and 0.8 (p = 0.7788), respectively. Conclusions: Concordant BAP1, MTAP, and p16 expression is found between cytological and corresponding histological samples, indicating that a reliable diagnosis of MPM can be made on cytology only. Of the three markers, BAP1 and MTAP are most reliable in distinguishing malignant from reactive mesothelial proliferations.

Diagnostic capacity of BAP1 and MTAP in cytology from effusions and biopsy in mesothelioma.

Serous effusion is often the first sign of mesothelioma. Diagnosis based on cytologic material from the effusions remains controversial and complementary biopsy is usually required. However, obtaining representative tissue sample may be challenging, while obtaining cytologic material is a minimally invasive procedure, providing potential for an earlier diagnosis. Loss of BRCA1-associated protein (BAP1), combined with loss of methylthionadenosine phosphorylase (MTAP) detected by immunohistochemistry, have shown to be reliable markers in the diagnosis of mesothelioma on histologic sections. Here we evaluate the value of these biomarkers in cytologic specimens. The BAP1 and MTAP expression in specimens of 162 mesothelioma patients (156 pleural, 6 peritoneal)-71 cytologic, 91 histologic (44 epithelioid, 31 biphasic, 16 sarcomatoid)-and 20 patients with reactive mesothelial proliferations were investigated. The loss of BAP1 and/or MTAP was highly sensitive and specific in differentiating mesothelioma from reactive mesothelial proliferations, with no significant difference between pleural effusions and biopsies, specificity of 100% in both and a sensitivity of 78.9% and 80.2%, respectively (P = 0.3). There was a 100% concordance of the expression of BAP1 and MTAP in cytologic and corresponding histopathologic samples. Loss of BAP1 and/or MTAP in histologic sections discriminated sarcomatoid, biphasic, and epithelioid mesothelioma from reactive mesothelial proliferations with a sensitivity of 81.2%, 83.9%, and 77.3% respectively. Loss of expression of BAP1 and/or MTAP differentiated mesothelioma from reactive mesothelial proliferations with excellent specificity and high sensitivity in cytologic samples, comparable to histopathologic sections.

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

AbstractBAP1 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.

IMMUNOHISTOCHEMICAL STUDY OF DESMIN, EPITHELIAL MEMBRANE ANTIGEN AND CALRETININ IN PLEURAL FLUID CELL BLOCK PREPARATIONS

Background: Distinction between reactive mesothelial cells, malignant mesothelioma and carcinoma is challenging in both biopsy and cytologic material. This study was conducted to differentiate benign/ reactive mesothelial proliferation from malignant mesothelial proliferations and metastatic adenocarcinoma by using immunohistochemical (IHC) markers Desmin (DES), Epithelial membrane antigen (EMA) and Calretinin (CAL) in pleural uid cell block (CB) preparations. A two year descriptive study (Oct.2016- Sept.2018). 46 pleural uids samples sentMethods : to the Dept. of Pathology, RIMS for routine examination and histopathological examination by CB preparation were studied using IHC markers EMA,DES and CAL following H & E stain. Out of 46 cases, 9(19.6%) cases were diagnosed as benign, 23(50.0%) as reactive andResults: 14(30.4%) as adenocarcinoma on H & E section by CB preparations within an age range 34 to 80 years (Mean±SE, 60.32±12.13). Following IHC staining with EMA, DES & CAL, 11(23.9%) cases were conrmed as benign, 17(37.0%) as reactive, 16(34.8%) as adenocarcinoma and 2(4.3%) cases as malignant mesothelioma. This study showed that EMA, DES and CAL helpful in conrming benign or reactive mesothelialConclusions: and malignant mesothelial with epithelial cells which will be helpful in providing appropriate diagnosis in difcult cases and provide better patient management.

Challenges and limitation of MTAP immunohistochemistry in diagnosing desmoplastic mesothelioma/sarcomatoid pleural mesothelioma with desmoplastic features

AimGenomic-based ancillary assays including immunohistochemistry (IHC) for BRCA-1 associated protein-1 (BAP1) and methylthioadenosine phosphorylase (MTAP), and fluorescence in situ hybridization (FISH) for CDKN2A are effective for differentiating pleural mesothelioma (PM) from reactive mesothelial proliferations. We previously reported a combination of MTAP and BAP1 IHC effectively distinguishes sarcomatoid PM from fibrous pleuritis (FP). Nevertheless, cases of sarcomatoid PM with desmoplastic features (desmoPM) are encountered where the IHC assessment is unclear. Methods and resultsWe evaluated assessment of MTAP IHC, BAP1 IHC, and CDKN2A FISH in 20 desmoPM compared to 24 FP. MTAP and BAP1 IHC could not be assessed in 11 (55 %) and 10 (50 %) cases, respectively, due to loss or faint immunoreactivity of internal positive control cells, while CDKN2A FISH could be evaluated in all cases. The sensitivities for MTAP loss, BAP1 loss, and CDKN2A homozygous deletion in desmoPM were 40 %, 10 %, and 100 %. A combination of MTAP loss and BAP1 loss yielded 45 % of sensitivity. ConclusionsMTAP IHC is a useful surrogate diagnostic marker in differentiating ordinary sarcomatoid PM from FP, but its effectiveness is limited in desmoPM. CDKN2A FISH is the most effective diagnostic assays with 100 % sensitivity and specificity in discriminating desmoPM from FP in the facilities where the FISH assay is available.

Usefulness of Cyclin D1/Podoplanin Dual Immunohistochemical Stain to Differentiate Malignant Mesothelioma From Reactive Mesothelial Proliferations.

To examine the potential of cyclin D1/podoplanin dual immunohistochemical stain to differentiate malignant mesothelioma from reactive mesothelial proliferations. Cyclin D1/podoplanin dual immunohistochemistry was performed on 34 surgical cases of reactive mesothelial proliferations, malignant mesothelioma, and nonmesothelioma malignancies. All 15 reactive mesothelial proliferations demonstrated less than 50% cyclin D1 staining with variable to diffuse podoplanin staining. In 6 (60%) of 10 cases of epithelioid malignant mesothelioma, the dual stain supported the diagnosis. Less than 50% cyclin D1 staining was noted in the remaining four cases, including small biopsy specimens or cases with focal papillary architecture. The five cases of sarcomatoid/desmoplastic/biphasic mesothelioma showed more than 50% cyclin D1 staining with focal to absent podoplanin staining. Well-differentiated papillary mesothelioma appears to demonstrate less than 25% cyclin D1 staining. The cyclin D1/podoplanin dual stain is reliable and may be used to aid in differentiation of benign mesothelial proliferations from malignant tumors. In addition, histologic features and other ancillary testing may support the classification of cases with an inconclusive cyclin D1/podoplanin staining.

Significance of p53 immunostaining in mesothelial proliferations and correlation with TP53 mutation status

p53 immunohistochemistry has long been proposed for the separation of benign from malignant mesothelial proliferations, with the older literature suggesting that any degree of positivity supported a diagnosis of mesothelioma. However, using modern immunohistochemistry platforms in other organ systems, notably gynecologic tumors, it has become clear that p53 staining can represent wild-type protein, and only specific staining patterns (absent, overexpression, or cytoplasmic expression) are indicative of a TP53 mutation. We applied these principles to two tissue microarrays containing 94 mesotheliomas and 66 reactive mesothelial proliferations. Seven/65 (11%) epithelioid mesotheliomas showed aberrant staining (four absent and three overexpression patterns) as did 5/29 (17%) of sarcomatoid mesotheliomas (all overexpression patterns). We sequenced the TP53 gene (exons 2–11) in five of the epithelioid and three of the sarcomatoid cases with aberrant staining as well as 12 epithelioid and eight sarcomatoid mesotheliomas with wild-type staining. All three sarcomatoid cases with aberrant staining showed mutated TP53, as did three of the epithelioid cases; in two of the epithelioid cases no mutation was detected, most likely because of large deletions not detected by this assay. In contrast, none of the 20 mesotheliomas with wild-type staining contained mutated TP53. We conclude that absent or overexpression p53 staining patterns can be used as a marker of a malignant vs. a benign mesothelial proliferation. The sensitivity of p53 staining by itself is low, but here addition of p53 to BAP1/MTAP staining increased sensitivity from 72 to 81% for epithelioid and 38 to 50% for sarcomatoid mesotheliomas.

The panorama of different faces of mesothelial cells.

All effusions in serous cavities represent a pathologic processes secondary to inflammatory, neoplastic, hemodynamic, or mechanical/traumatic etiologies. This elicits reactive changes in the extremely sensitive mesothelial cells lining the serosal surfaces. The result is hypertrophy and hyperplasia which lead to broad changes with a wide range of morphological appearances. These reversible alterations may resolve entirely after the recovery of underlying pathology.Under the tertiary care situations, neoplastic effusion specimens are encountered more frequently. Although some non-neoplastic pathologic process may demonstrate a few diagnostic features, cytologic evaluation of malignant effusions usually show diagnostic malignant cells. However, the most versatile mesothelial cells demonstrate a very wide cytomorphological spectrum secondary to reactive challenges. These mesothelial cells are usually referred to as ‘reactive mesothelial cells’. In addition other terms such as reactive mesothelial proliferation, reactive mesothelial hyperplasia, irritated mesothelial cells, activated mesothelial cells, hyperplastic mesothelial cells, hypertrophic mesothelial cells, and proliferative mesothelial cells. Rarely atypical mesothelial cells, although not recommended, is used inadvertently. Although there is a lack of general agreement defining these terms, some of these including atypical mesothelial cells, should not be preferred. With reference to this CMAS series, usually favored term ‘reactive mesothelial cells’ is preferred.The size of reactive mesothelial cells range from 15 to 30 µm (but may be up to 50 µm). These polyhedral cells with variable amount of cytoplasm and enlarged nuclei may show variation in sizes and shapes with conspicuous nucleoli. Bi- and multi-nucleation is frequent. Cohesive groups of mesothelial cells as sheets and three dimensional groups may be present. Some floridly reactive mesothelial cells with hyperchromatic enlarged nuclei with prominent nucleoli and scant cytoplasm may resemble malignant cells. This astonishingly wide morphological spectrum of reactive mesothelial cells is a significant interpretation challenge in effusion fluid cytology. Methodical interpretation approach with appropriate knowledge about this wide spectrum is important aspect in diagnostic cytopathology of effusion fluids.

Correlation of MET-Receptor Overexpression with MET Gene Amplification and Patient Outcome in Malignant Mesothelioma.

Thanks to clinically newly introduced inhibitors of the mesenchymal–epithelial transition (MET) receptor tyrosine-kinase, MET-gene copy number gain/amplification (MET-GCNG/GA) and increased expression of the MET protein are considered very promising therapeutic targets in lung cancer and other malignancies. However, to which extent these MET alterations occur in malignant mesothelioma (MM) remains unclear. Thus, we investigated by well-established immunohistochemistry and fluorescence in situ hybridization methods, the frequency of these alterations in specimens from 155 consecutive MMs of different subtypes obtained from pleural or peritoneal biopsies and pleurectomies. Thirty-three benign reactive mesothelial proliferations (RMPs) were used as controls. MET-protein upregulation was observed in 35% of all MM-cases, though restricted to predominantly epithelioid MMs. We detected low-/intermediate-level MET-GCNG/GA in 22.2% of MET-overexpressing MMs (7.8% of whole MM-cohort) and no MET-GCNG/GA in the other 77.8%, suggesting other upregulating mechanisms. In contrast, 100% of RMPs exhibited no MET-upregulation or MET-GCNG/-GA. Neither MET exon 14 skipping mutations nor MET-fusions were detected as mechanisms of MET overexpression in MM using RNA next-generation sequencing. Finally, in two cohorts of 30 MM patients with or without MET overexpression (MET-positive/-negative) that were matched for several variables and received the same standard chemotherapy, the MET-positive cases showed a significantly lower response rate, but no significant difference in progression-free or overall survival. Our results imply that MET overexpression occurs in a substantial fraction of predominantly epithelioid MMs, but correlates poorly with MET-amplification status, and may impact the likelihood of response to mesothelioma standard chemotherapy. The predictive significance of MET-IHC and -FISH for possible MET-targeted therapy of MM remains to be elucidated.

UHRF1 Immunohistochemical Staining Separates Benign Reactive Spindle Cell Mesothelial Proliferations From Sarcomatoid Mesotheliomas.

The separation of benign from malignant mesothelial proliferations is often a difficult pathologic problem. UHRF1 (ubiquitin-like with plant homeodomain and ring finger domains-1) is a regulator of DNA methylation and an epigenetic driver of various human cancers. It has recently been reported that UHRF1 is overexpressed in mesotheliomas. We asked whether UHRF1 immunohistochemistry could be used to separate benign from malignant mesothelial proliferations. Initial studies showed that UHRF1 stained mesothelial cells but also endothelial and other non-neoplastic cells, so that accurate counting of positive mesothelial cells was difficult. Therefore, we ran dual UHRF1-AE1/AE3 stains on 2 tissue microarrays containing 40 reactive mesothelial proliferations and 61 mesotheliomas and only counted UHRF1 staining in keratin-positive cells. On average 10.3±8.6% (mean±SD; range: 0% to 36, median: 6.8%) of epithelioid mesothelioma cells stained compared with 5.3±4.8% (range: 0% to 15%, median: 4.1%) of reactive epithelial mesothelial cells. This difference was statistically significant but there was too much overlap to use diagnostically. In contrast, 37±26% (range: 2.5% to 95%, median: 31%) of cells in sarcomatoid mesotheliomas compared with 1.2±1.2% (range: 0% to 3.0%, median: 1.0%) of cells in reactive spindle cell mesothelial proliferations stained. To confirm this difference we stained whole sections of 21 sarcomatoid mesotheliomas and 19 cases of organizing pleuritis. Staining of mesothelial cells was seen in 2.1±2.4% (range: 0% to 6.8%, median: 1.0%) of organizing pleuritis cases and 44±22% (range: 14% to 90%, median: 41%) of sarcomatoid mesotheliomas. We conclude that dual UHRF1-AE1/AE3 immunohistochemistry is very useful for separating benign spindle cell mesothelial proliferations from sarcomatoid mesotheliomas.

The Collagen Receptor uPARAP in Malignant Mesothelioma: A Potential Diagnostic Marker and Therapeutic Target.

Malignant mesothelioma (MM) is a highly aggressive cancer with limited therapeutic options. We have previously shown that the endocytic collagen receptor, uPARAP, is upregulated in certain cancers and can be therapeutically targeted. Public RNA expression data display uPARAP overexpression in MM. Thus, to evaluate its potential use in diagnostics and therapy, we quantified uPARAP expression by immunohistochemical H-score in formalin-fixed paraffin-embedded bioptic/surgical human tissue samples and tissue microarrays. We detected pronounced upregulation of uPARAP in the three main MM subtypes compared to non-malignant reactive mesothelial proliferations, with higher expression in sarcomatoid and biphasic than in epithelioid MM. The upregulation appeared to be independent of patients’ asbestos exposure and unaffected after chemotherapy. Using immunoblotting, we demonstrated high expression of uPARAP in MM cell lines and no expression in a non-malignant mesothelial cell line. Moreover, we showed the specific internalization of an anti-uPARAP monoclonal antibody by the MM cell lines using flow cytometry-based assays and confocal microscopy. Finally, we demonstrated the sensitivity of these cells towards sub-nanomolar concentrations of an antibody-drug conjugate formed with the uPARAP-directed antibody and a potent cytotoxin that led to efficient, uPARAP-specific eradication of the MM cells. Further studies on patient cohorts and functional preclinical models will fully reveal whether uPARAP could be exploited in diagnostics and therapeutic targeting of MM.

LEFT-SIDED PLEURAL EFFUSION, ASCITES AND LEIOMYOMATA: AN UNUSUAL CASE OF PSEUDO-MEIGS' SYNDROME

TOPIC: Disorders of the Pleura TYPE: Medical Student/Resident Case Reports INTRODUCTION: Meigs' Syndrome has been described as the development of ovarian fibroma or fibroma-like mass with pleural effusion and ascitic fluid. It is present in approximately 1% of all ovarian fibroma, thecoma and granulosa cell tumors. Pseudo-Meigs' Syndrome is secondary to benign etiologies and reported to be more uncommon. These syndromes should be considered in women with the clinical triad of pleural effusion, ascites and a pelvic mass and can mimic more serious malignant tumors [1]. A thorough evaluation including biopsy and peritoneal and pleural fluid analyses need to be performed. CASE PRESENTATION: A G0P0 29-year-old female presents with chills and fatigue since the start of her menstrual cycle. She was found to be tachycardic, tachypneic and hypoxemic to 85% with moderate abdominal distention. CT of the chest, abdomen and pelvis showed a large left-sided pleural effusion, multiple abdominal masses with compressive effect and large-volume abdominal ascites. CA-125 level was elevated at 295 U/ml. Biopsy showed small muscle proliferation with bland spindle cells and no malignant features. Thoracentesis was consistent with exudative effusion and negative cytology. Left-sided pleural effusion continued to reaccumulate requiring multiple thoracenteses. Patient underwent left pleuroscopy with pleural biopsies showing fibrotic pleura and reactive mesothelial proliferation, negative for malignancy. There was an active ascitic fluid leak into the left hemithorax through a small, thinned-out region in the dome of the left hemidiaphragm. She underwent abdominal myomectomy several months later with resolution of symptoms. Final pathology was consistent with leiomyomata. DISCUSSION: We describe a case of abdominal leiomyomatosis resulting in ascites and leak into the left hemithorax with recurrent exudative pleural effusions and resolution after surgical myomectomy, consistent with Pseudo-Meigs' Syndrome [2]. Right-sided pleural effusions are most common as pleural fluid collects due to fluid leakage from edematous tumor resulting in translocation via diaphragmatic pores into the right hemidiaphragm [3]. Effusions are exudative in nature, although in previous studies only 1.6% of patients underwent pleural fluid analysis [4]. CA-125 are typically found to be elevated, with normalization post-surgery [5]. CA-125 levels were not re-checked post-myomectomy in our case. Surgical tumor removal results in resolution of ascites and pleural effusion [5]. Therefore, in patients presenting with pleural effusion and ascites in the setting of abdominal leiomyomata, Pseudo-Meigs' Syndrome should be suspected, and pleural fluid analysis and cytology play an important role in aiding diagnosis and further management. CONCLUSIONS: The prompt evaluation of patients with leiomyomatosis presenting with ascites and large pleural effusion can be vital in guiding future interventional management. REFERENCE #1: 1. Cowan M, Crantz J, Welsh S, Nahhas W, Lindheim SR. A rare case of acute pseudo-Meigs' Syndrome presenting with pleural effusion and ascites and a ruptured leiomyoma and hemorrhagic shock. Obstet Gynecol Cases Rev. 2016. 3:070. REFERENCE #2: 2. Peparini N, Chirletti P. Ovarian malignancies with cytologically negative pleural and peritoneal effusions: demons' or meigs' pseudo-syndromes? Int J Surg Pathol. 2009 Oct; 15(5):396-7.3. Meyers MA. The spread and localization of acute intraperitoneal effusions. Radiology. 1970 Jun;95(3):547-54. REFERENCE #3: 4. Krenke R, Maskey-Warzechowska M, Korczynski P et al. Pleural effusion in Meig's syndrome - transudate or exudate? Systematic review of the literature. Medicine (Baltimore). 2015 Dec; 94(49): e2114.5. Nguyen P, Yazdanpanah O, Schumaker B. Meigs' versus Pseudo-Meigs' Syndrome: A case of pleural effusion, ascites, and ovarian mass. Cureus. 2020 Aug; 12(8): e9704. DISCLOSURES: No relevant relationships by Sally Askar, source=Web Response No relevant relationships by Patrick Bradley, source=Web Response No relevant relationships by Labib Debiane, source=Web Response No relevant relationships by Shaikh Husnain, source=Web Response

State‐of‐the‐art cytology of pleural fluid, focusing on the diagnosis of mesothelioma

Mesothelioma has always been a challenging diagnosis to render in body cavity cytology samples. This review is a timely update on pleural fluid cytology and ancillary studies that should be considered in the diagnosis of mesothelial proliferations, specifically mesotheliomas. Information about new diagnostic approaches and ancillary studies in mesothelioma was obtained from the peer-reviewed literature and the authors' experiences. Although the morphological diagnosis of mesothelioma is fraught with numerous challenges given the overlap with other diagnostic entities, there are a variety of immunohistochemical and fluorescence in situ hybridization studies available to help in determining mesothelial origin and in distinguishing malignant proliferations from the more common benign or reactive mesothelial proliferations. Although ancillary studies can be helpful, there are important pitfalls to be aware of when interpreting these cases, and this review highlights some of the challenges that require caution.

Membranous HEG1 expression is a useful marker in the differential diagnosis of epithelioid and biphasic malignant mesothelioma versus carcinomas.

Sialylated HEG1 has been reported as a highly specific and sensitive mesothelioma marker but a comprehensive evaluation of its expression in carcinomas in different organs, various sarcomas and reactive mesothelial proliferations has not been reported. The aim of this study was to evaluate the clinical applicability of HEG1 as a marker in the diagnosis of mesothelioma. HEG1 immunoreactivity was evaluated in whole sections of 122 mesotheliomas, 75 pulmonary carcinomas, 55 other carcinomas, 16 mesenchymal tumors, and 24 reactive mesothelial proliferations and in tissue microarrays containing 70 epithelioid (EM), 36 biphasic (BM), and 2 sarcomatoid mesotheliomas (SM). In whole sections and tissue microarrays, respectively, membranous HEG1 was expressed in 93.0% and 85.5% of EM, 81.3% and 69.4% of BM, 0% and 0% of SM. HEG1 was not expressed in pulmonary adenocarcinomas. HEG1 was expressed as cytoplasmic immunoreactivity in pulmonary squamous cell carcinomas (21.7%). Membranous HEG1 staining was seen in ovarian carcinomas (66.7%), thyroid carcinomas (100%), reactive conditions (16.7%), and mesenchymal tumors (18.8%). The sensitivity of membranous HEG1 expression to distinguish EM/BM from all carcinomas was 88.8%. The specificity for the differential diagnosis between EM/BM and all carcinomas and pulmonary carcinomas was 92.3% and 98.7%, respectively.

Immunochemistry in the work-up of mesothelioma and its differential diagnosis and mimickers.

The differential diagnosis in cellular effusions with cytological atypia often includes malignant mesothelioma (MM), reactive mesothelial proliferation, and malignancies of metastatic origin, particularly carcinomas. The International Reporting System for Serous Fluid recently established guidelines for reporting MM. In conjunction with the cytomorphologic evaluation, the role of immunochemistry (IC) was emphasized as a very useful tool in the workup of serous fluids, especially with the availability of novel markers. Utilizing a panel of markers, IC allows the characterization of the cells, whether mesothelial or not, and when mesothelial origin is established, IC can frequently assist in delineating its benign or malignant nature. IC can also confirm metastatic disease, allowing the identification of the primary origin in most cases. This review summarizes the current status of IC and its role in the diagnosis of MM and its differential diagnosis in serous fluids.

ES17.04 Updates in Mesothelioma

The histologic subtype of malignant mesothelioma of the pleura has an impact on prognosis and treatment decisions and therefore has to be documented in diagnostic pathology reports. Epithelioid morphology is associated with a better prognosis when compared to sarcomatoid and biphasic subtypes. Surgical treatment may also have a prognostic impact in epithelioid subtype, while the same benefit is not seen in biphasic and sarcomatoid mesotheliomas. The 2020/21 WHO classification divides mesothelial proliferations into benign and preinvasive (adenomatoid tumor, well-differentiated papillary mesothelial tumor, mesothelioma in situ) and mesothelioma (localized pleural mesothelioma, diffuse pleural mesothelioma). The main change is the introduction of mesothelioma in situ (MIS) in the classification. Until recently the consensus was that MIS cannot be separated from reactive surface mesothelial proliferations on morphology alone. However, the concept of MIS was recently reintroduced for surface, usually flat or simple papillary, mesothelial proliferations with loss of BAP1 nuclear staining by immunohistochemistry or CDKN2A homozygous deletion, in the absence of radiologic or clinical gross evidence of the disease.1-3 Clinically, MIS is suspected in patients with unexplained recurrent effusions in the setting of heavy asbestos exposure, after irradiation and in patients with familial predisposition. The diagnosis requires sufficient tissue usually large biopsy samples. Small biopsy and cytology samples are not appropriate. Patients with MIS have a high incidence of eventual development of invasive mesothelioma. The updated classification of epithelioid mesotheliomas includes architectural patterns (tubular, papillary, tubulopapillary, trabecular, solid, adenomatoid and microcystic), stromal (myxoid) and cytologic (pleomorphic ,rhabdoid, deciduoid, small cell, clear cell, signet ring) features. Their identification is important for correct diagnosis, and some have prognostic values. Two cytologic features, transitional and pleomorphic, were previously classified as epithelioid patterns. They have shown a similar survival to biphasic and sarcomatoid mesothelioma and should be reclassified.5-8 Transitional features have appearance between epithelioid and sarcomatoid morphology, and have genomic characteristics similar to sarcomatoid subtype, and therefore were reclassified as cytologic feature of sarcomatoid mesothelioma. 6. Epithelioid mesotheliomas with transitional features should be reclassified as biphasic mesothelioma. Transitional features within biphasic mesothelioma carry negative prognostic significance, with a median survival of 6 months for cases with transitional features compared to 12 months for those without transitional features .6 Pleomorphic features, as described in epithelioid mesothelioma, can also be seen in sarcomatoid mesotheliomas. In contrast to transitional features, emerging genomic data suggest that a mesothelioma with pleomorphic features genomically can cluster with either sarcomatoid or epithelioid subtypes. Therefore, mesotheliomas with pleomorphic features should be classified based on the most predominant morphology as either sarcomatoid or epithelioid. A two-tier grading system for epithelioid mesothelioma allows the identification of more aggressive mesotheliomas and can be applied to biopsy and resection specimens 9, 10 It is primarily based on the combination of nuclear features, mitotic rate and the presence or absence of necrosis (Figure 1). Molecular testing in mesothelioma compared to other cancers is very limited. Recently, there have been several sequencing efforts to provide insights into the genomic characteristics and improved prognostic classification of mesothelioma. 10

Diagnostic Utility of BRCA1-Associated Protein 1 (BAP1) in Distinguishing Reactive and Neoplastic Mesothelial Proliferation

Background: Malignant mesothelioma (MM) is an aggressive tumor which arises from the lining of serous cavities. Distinguishing between begnin and malignant mesothelial proliferation on effusions is a challenge. This study aims to evaluate the diagnostic utility of BAP1 in distinguishing MM from reactive mesothelial proliferation.Material and methods: This is a retrospective study on 61 cases; pleural biopsies (n=36) and pleural cell blocks (n=25). Included were synchronous cytology/ biopsy pair samples. All cases were stained with BAP-1antibody using avidin-biotin complex. BAP1 immunohistochemistry was evaluated using cut off value; negative staining indicate malignancy. Statistical analysis was done using SPSS (version 20), P value (P value <0.05 was considered statistically significant). ROC curve to predict cut off value.Results: In MM cases 61.1% showed BAP1 negative nuclear expression. In reactive mesothelial proliferation cases; 20% showed BAP1 negative expression. In atypical mesothelial proliferation cases, 80% showed BAP1 negative nuclear expression. synchronous cytology/ biopsy pairs (13 cases) showed BAP1 matching results. There was a highly statistically significant correlation between BAP1 expression and the study groups (P-value <0.001). There was statistically significant correlation between BAP-1 expression and histological types of mesothelioma (P-value <0.05) and stage (P-value <0.05). In cell blocks; sensitivity was 80% and specificity was 80% for atypical mesothelial proliferation. In tissue biopsy; sensitivity was 61.1% and Specificity was 80% for mesothelioma.Conclusion: In effusions, negative BAP1 strongly support the diagnosis of malignant mesothelioma, so BAP1 may be included in immunohistochemical panels for malignant mesothelioma cytodiagnosis.