Evaluating Diagnostic Clarity: The Comparative Efficacy of BlueStain in Serous Effusion Cytology under the International System for Reporting Serous Fluid Cytopathology Reporting Framework.

Serous effusion cytology is a pivotal diagnostic and staging tool in clinical pathology, valued for its simplicity and cost-effectiveness. Staining techniques such as Giemsa and Papanicolaou are foundational, yet the search for rapid and efficient alternatives continues. Our study assesses the efficacy of an in-house-developed BlueStain, a toluidine blue variant, within the International System for Reporting Serous Fluid Cytopathology (TIS), aiming to optimize diagnostic clarity and resource use. MATERIALS AND METHODS: This section provides details on the cohort of 237 patients with serous effusions, the ethical approval process, sample collection, and staining procedures with BlueStain, Papanicolaou, and Giemsa. It also describes the microscopic evaluation criteria, scoring system, and statistical methods used to compare the stains. RESULTS: BlueStain demonstrated notable performance, particularly in identifying malignant cells, presenting a competitive alternative to the Papanicolaou stain, which, despite higher quality indices in other categories, requires more resources and time. The study revealed that BlueStain might offer a valuable balance between quality and efficiency, especially in cases where rapid diagnostic turnaround is essential. CONCLUSIONS: Our findings suggest that BlueStain is a viable staining method in the context of serous effusions, capable of providing detailed cytomorphological analysis. While traditional stains hold their place for their established diagnostic clarity, BlueStain offers a rapid and resource-optimized alternative. The absence of definitive diagnostic criteria in the atypical category and the inherent sample heterogeneity underscores the necessity for adaptable staining methods like BlueStain. The study highlights the potential trade-offs between detail and practicality in staining techniques, advocating for further research into innovative methods that do not compromise diagnostic precision for cost and time efficiency.

Hepatic insufficiency in two juvenile dogs with histoplasmosis.

A 9-month-old female intact toy poodle and a 1-year-old female intact Labrador retriever mix presented to separate teaching hospitals for chronic histories of malaise and clinicopathologic evidence of hepatic dysfunction. The signalment and clinical histories of these dogs prompted consideration of a congenital portosystemic shunt as a primary differential. However, microscopic evaluation of peritoneal effusion, pleural effusion, and peripheral blood samples from the dogs revealed round to ovoid yeast organisms morphologically most compatible with Histoplasma capsulatum. Additional testing confirmed histoplasmosis in each case. The poodle underwent a computed tomography (CT) study, which showed hepatomegaly with a spleno-gonadal shunt, pancreatic and gastric wall edema, and marked peritoneal effusion, findings compatible with portal hypertension and secondary acquired shunt formation. The dog was later humanely euthanized due to clinical deterioration, and on necropsy hepatic histoplasmosis was verified, with additional affected tissues comprising lungs and spleen. The Labrador Retriever mix responded clinically and clinicopathologically to antifungal therapy, though no abdominal imaging was performed to definitively exclude the possibility of a congenital portosystemic shunt. In retrospect, several features were more compatible with histoplasmosis than portosystemic shunt in these cases, including hyperbilirubinemia, effusion, and hepatomegaly. These findings serve as a reminder of the need to interpret serum biochemical findings in the context of the totality of the clinicopathologic data and imaging findings, as well as the diagnostic value of microscopy in the evaluation of hematologic and body cavity fluid samples.

Optimal Volume Assessment for Serous Fluid Cytology.

OBJECTIVE: This study aimed to investigate the optimal volume of serous fluid needed for accurate diagnosis using The International System for Reporting Serous Fluid Cytopathology (TIS), as well as to provide information on the distribution of serous effusion cases in the TIS categories (ND: non-diagnostic, NFM: negative for malignancy, AUS: atypia of undetermined significance, SFM: suspicious for malignancy, MAL: malignant) and relevant epidemiological data. METHODS: A retrospective analysis of 2340 serous effusion cases (pleural, peritoneal, and pericardial) from two hospitals between 2018 and 2020 was conducted. TIS categories were assigned to each case, and for 1181 cases, these were correlated with the volume of the analyzed fluid. RESULTS: Our study found statistically significant differences in volume distributions between certain TIS categories. Statistically lower volumes were observed in NFM compared to MAL, in UNCERTAIN (ND, AUS, SFM) compared to both MAL and NFM, and in NOT MAL (ND, NFM, AUS, SFM) compared to MAL. However, these differences were not substantial enough to hold any clinical relevance. CONCLUSIONS: This study suggests that while fluid volume may slightly influence the TIS category, it does not impact the diagnostic accuracy of serous effusion cytology. Therefore, the ideal serous effusion specimen volume can be defined solely by practical parameters.

Diagnostic accuracy of International System for Reporting Serous Fluid Cytopathology: A systematic review and meta-analysis in malignancy diagnosis.

This study conducts the first meta-analysis to assess the aggregated risk of malignancy associated with each category of the International System for Reporting Serous Fluid Cytopathology (ISRSFC) for reporting serous effusion cytology, while also evaluating diagnostic accuracy. PubMed/MEDLINE and Embase were systematically searched using the keywords "(pleural, peritoneal, and pericardial effusions) AND (serous effusion cytology) OR (International System for Reporting Serous Fluid Cytopathology)". Articles underwent risk of bias assessment using the QUADAS-2 tool. After excluding inadequate samples, a meta-analysis determined sensitivity and specificity for different cutoff points, including "atypical considered positive," "suspicious of malignancy considered positive," and "malignant considered positive." Summary receiver operating characteristic curves assessed diagnostic accuracy, and the diagnostic odds ratio was pooled. Sixteen retrospective cross-sectional studies, totaling 19,128 cases, were included. Sensitivity and specificity for the "atypical and higher risk categories" considered positive were 77% (95% confidence interval [CI], 68%-84%) and 95% (95% CI, 93%-97%) respectively. For the "suspicious for malignancy and higher risk categories" considered positive, sensitivity and specificity were 57% (95% CI, 49%-65%) and 100% (95% CI, 99%-100%) respectively. Sensitivity and specificity for the "malignant" category considered positive for malignancy were 70% (95% CI, 60%-77%) and 99% (95% CI, 98%-99%), respectively. The pooled area under the curve ranged from 85% to 89.5% for each cutoff. This meta-analysis underscores the ISRSFC's accuracy in reporting serous fluid cytology. It emphasizes the diagnostic importance of the "suspicious" and "malignant" categories in identifying malignancy, and the role of the "benign" category in ruling out malignancy.

A Novel Validated Real-World Dataset for the Diagnosis of Multiclass Serous Effusion Cytology according to the International System and Ground-Truth Validation Data.

INTRODUCTION: The application of artificial intelligence (AI) algorithms in serous fluid cytology is lacking due to the deficiency in standardized publicly available datasets. Here, we develop a novel public serous effusion cytology dataset. Furthermore, we apply AI algorithms on it to test its diagnostic utility and safety in clinical practice. METHODS: The work is divided into three phases. Phase 1 entails building the dataset based on the multitiered evidence-based classification system proposed by the International System (TIS) of serous fluid cytology along with ground-truth tissue diagnosis for malignancy. To ensure reliable results of future AI research on this dataset, we carefully consider all the steps of the preparation and staining from a real-world cytopathology perspective. In phase 2, we pay special consideration to the image acquisition pipeline to ensure image integrity. Then we utilize the power of transfer learning using the convolutional layers of the VGG16 deep learning model for feature extraction. Finally, in phase 3, we apply the random forest classifier on the constructed dataset. RESULTS: The dataset comprises 3,731 images distributed among the four TIS diagnostic categories. The model achieves 74% accuracy in this multiclass classification problem. Using a one-versus-all classifier, the fallout rate for images that are misclassified as negative for malignancy despite being a higher risk diagnosis is 0.13. Most of these misclassified images (77%) belong to the atypia of undetermined significance category in concordance with real-life statistics. CONCLUSION: This is the first and largest publicly available serous fluid cytology dataset based on a standardized diagnostic system. It is also the first dataset to include various types of effusions and pericardial fluid specimens. In addition, it is the first dataset to include the diagnostically challenging atypical categories. AI algorithms applied on this novel dataset show reliable results that can be incorporated into actual clinical practice with minimal risk of missing a diagnosis of malignancy. This work provides a foundation for researchers to develop and test further AI algorithms for the diagnosis of serous effusions.

Bugs' eyes and black monsters: Ascitic fluid cytology in an elderly male with hematochezia.

Anorectal malignant melanomas are rare, accounting for less than 2% of all melanomas. Malignant effusions developing secondary to malignant melanoma are highly uncommon. Herein, we present the cytomorphological features of a metastatic anorectal malignant melanoma presenting with ascites at the initial clinical presentation.

Massive Myelomatous Pleural Effusion With Contralateral Mediastinal Shift: A Unique Presentation of Extramedullary Myeloma.

Multiple myeloma (MM) is a relatively common malignancy that primarily affects the bone marrow, while extramedullary disease (EMD) occurs in the skin and muscle, lung pleura, lymph nodes, liver, and CNS. Myelomatous pleural effusion (MPE) is a rare extramedullary manifestation of MM in which pleural fluid is composed almost entirely of abnormal plasma cells. MPE and other types of EMD are associated with poor prognosis, and MPE can present emergently due to tension physiology. We report a case of a patient with massive MPE presenting with contralateral midline shift. There are exceedingly few such cases and this report highlights a unique presentation of this rare clinical entity. Epidemiology, radiographic features, diagnosis, treatment, and implications for the prognosis of the disease are discussed.

Effusion cytology of metastatic carcinosarcoma.

Objectives: Carcinosarcomas (CSs) are rare gynecological neoplasms seen in elderly females. These are composed of malignant epithelial and mesenchymal components, which appear as adenocarcinoma and high-grade sarcoma. Effusions are encountered uncommonly in CS. Material and Methods: The study focuses on the cytomorphology of 10 cases of metastatic CS in effusions. In 6 years, there were 10 (0.45%) cases of metastatic CS in effusion samples out of 2240 malignant effusion samples. The samples were processed by SurePath™ and centrifuge technique. Both May-Grünwald-Giemsa and Papanicolaou stained smears were evaluated for cytomorphological features, and the findings were correlated with subsequent histopathology. Results: The cells were predominantly arranged in ball-like clusters and discretely. The cells had abundant vacuolated cytoplasm and enlarged pleomorphic nuclei. Occasional cases showed scattered spindle cells. The cases were diagnosed as metastatic adenocarcinoma (7/10) and positive for malignant cells (3/10). None of the cases was diagnosed as CS. The primary of these cases was in the uterus (7/10) and ovary (3/10). Conclusion: The cytological evaluation of such effusion samples rarely demonstrates the classical biphasic pattern of these tumors. Mostly, the carcinomatous component is evident, and the sarcomatous element is inapparent and readily missed.

Diagnostic Utility of Claudin4 and Comparison with BerEp4 as a Marker for Metastatic Adenocarcinoma in Serous Effusions.

INTRODUCTION: Fluid cytology for malignant cells is important for diagnosis and staging of malignancies. Morphological overlap between reactive mesothelial cells and adenocarcinoma poses challenges, for which many immunohistochemical markers like BerEp4 and MOC-31 have been used extensively. Claudin4 is a new marker with promising results; however, further studies are required to establish its role as a pan-carcinoma marker in serous effusions. This study aimed to determine the utility of Claudin4 in diagnosing metastatic adenocarcinoma in effusions and comparing its performance with BerEp4. METHODS: Claudin4 immunohistochemistry (IHC) was performed on effusion cell blocks (n = 60) reported as positive or suspicious for metastatic adenocarcinoma on cytology over a 1-year period and was scored for intensity (0-3) and percentage of positive cells (0-4). The results were compared with BerEp4 IHC and correlated with follow-up. Ten benign effusions were included as negative controls. RESULTS: Claudin4 IHC was positive in all 60 (100%) cases, irrespective of the primary site. BerEp4 IHC was positive in 58 (96.7%) fluids and negative in 2 (3.3%) cases. All 10 benign effusions were negative for Claudin4 and BerEp4. Claudin4 showed higher intensity and proportion scores as compared to BerEp4 in cases where tumor cells were predominantly singly scattered and was comparable to BerEp4 where tumor cells were arranged in groups. Sensitivity, specificity, PPV, and NPV of Claudin4 in our study was 100%. Sensitivity, specificity, PPV, and NPV of BerEP4 was 96.7%, 100%, 100%, and 83.3%, respectively. CONCLUSION: Claudin4 IHC staining results were comparable to BerEp4, irrespective of the primary site, and it performed better in cases where tumor cells were predominantly scattered singly.

Application of international system for reporting serous fluid cytology (ISRSFC) in effusion samples-a prospective study in an oncology setting.

INTRODUCTION: Serous fluid cytology is a cost-effective procedure that can help in the diagnosis, staging, and origin of the malignancy. Recently introduced International System for Reporting Serous Fluid Cytology (ISRSFC) standardizes the reporting of serous fluid cytology in the 5 categories: Category 1: Nondiagnostic (ND), Category 2: negative for malignancy (NFM), Category 3: atypia of undetermined significance (AUS), Category 4: suspicious for malignancy (SFM), and Category 5: malignant (MAL). Here, we present our experience adopting the ISRSFC. MATERIALS AND METHODS: We implemented ISRSFC in December of 2019 at our institute and included a cohort of 555 prospective effusion samples. The pertinent surgical pathology, radiology, and clinical follow-up were also extracted to assess the risk of malignancy (ROM) and performance parameters. RESULTS: The assessment of interobserver reliability indicated substantial concordance (κ = 0.717) between the 2 investigators for serous fluid categorization. A total of 555 effusion samples were classified as follows: ND, 14 (2.5%); NFM, 394 (71%); AUS, 12 (2.2%); SFM, 13 (2.3%); and MAL, 122 (22%). The ROM for the ND, NFM, AUS, SFM, and MAL categories was 57.1%, 9.9%, 66.7%, 66.7%, and 97.2%, respectively, in peritoneal effusions and 57.1%, 7.1%, 66.7%, 100%, 100%, respectively, in pleural effusions. The ROM for NFM and MAL was 0% and 100%, respectively, in pericardial effusion. CONCLUSIONS: Application of the proposed ISRSFC can help in achieving uniformity and reproducibility in diagnoses and also help in risk stratification in cytology. ISRSFC was successfully adopted by our cytology laboratory and clinicians, with overall diagnostic performance similar to previous studies.

Number Needed to Diagnose in Malignant Ascites: Effects of Volume, Repeating Collection, and Primary Malignancy on Diagnostic Performance in Peritoneal Fluid Cytology.

INTRODUCTION: Volume recommendations of 80-200 mL have been proposed for peritoneal fluid cytology. While cutoffs are impractical when volume is limited by the amount present and disease factors, collections, however, can be repeated. This study addresses adequacy and number needed to diagnose by comparing diagnostic agreement to volumes in single specimens, total volumes collected daily, and within admissions. The diagnostic yield of repeating collection within a single day, admission, and throughout admissions of a patient's lifetime was also investigated. METHODS: Peritoneal fluid cytology specimens over a 27-year period were retrieved and matched by collection date, admission number, and patient number. Case notes were reviewed to establish all cases of malignant ascites. RESULTS: In total, 19,392 specimens from 14,327 admissions and 11,089 patients were retrieved, with 1,531 patients confirmed with malignant ascites. Agreements between cytologic diagnoses within the same day and admission were high (κ > 0.8). Fluid volume increased with grade of cytologic diagnosis (p < 0.001), and greater volume was associated with higher discordance (p < 0.05). Specimens of 60-100 mL showed the best diagnostic concordance. To achieve a 99.5% diagnostic rate, three sequential aliquots, collections from two different days in an admission, or three admissions within a lifetime are required. The diagnostic yield of one aliquot within batches from the same day was only 88.9%. Gastrointestinal (p = 0.040), gynecologic (p = 0.005), and lung (p < 0.001) malignancies required the least repeats for diagnosis. CONCLUSIONS: Omission of any fluid from laboratory submission is strongly discouraged. As a simple rule, three repeats are necessary for excluding malignant ascites.

Utility of TRPS1 in Malignant Effusion Cytology.

INTRODUCTION: Identifying metastatic breast carcinoma (mBC) in malignant effusion cytology (MEC) specimens is critical, as this will determine the patient's prognosis and therapeutic management. Overlapping cytomorphologic features of breast carcinoma (BC) with other neoplastic entities makes the use of sensitive and specific markers highly desirable. Recent studies have reported trichorhinophalangeal syndrome type 1 (TRPS1) as a sensitive and specific marker for primary BC and mBC. We aimed to investigate TRPS1 expression in MEC of mBC and its most common diagnostic mimickers. MATERIALS AND METHODS: A retrospective search from the pathology archives identified 82 MEC. TRPS1 expression in mBC was analyzed, and the results were compared to those in metastatic carcinoma of Müllerian origin (mMC) and metastatic pulmonary adenocarcinoma (mPAC). TRPS1 immunoperoxidase was performed on cytospin or cell block preparations, and p < 0.05 was considered significant. RESULTS: Nuclear expression for TRPS1 was evaluated and scored as positive (≥1% of tumor cells) or negative. Nuclear TRPS1 expression was seen in 100% (30/30) mBC, 72% (18/25) mMC, and 7% (2/27) mPAC. This resulted in sensitivity, specificity, positive predictive value, and negative predictive values of 100%, 61%, 60%, and 100%, respectively. CONCLUSION: TRPS1 is a sensitive marker for mBC and can be reliably performed on cytology specimens. TRPS1 expression was also identified in a significant proportion of mMC, creating a potential diagnostic pitfall. Therefore, caution should be exercised when evaluating MEC of mBC with TRPS1. Consequently, a combination of immunoperoxidase panels should be employed in this setting.

The diagnostic utility of trichorhinophalangeal syndrome type 1 immunohistochemistry for metastatic breast carcinoma in effusion cytology specimens.

BACKGROUND: Trichorhinophalangeal syndrome type 1 (TRPS1) is a novel immunohistochemical marker with excellent performance in distinguishing breast carcinoma from other cancers in surgical specimens. The aim of this study was to evaluate the diagnostic utility of TRPS1 compared with GATA3 for metastatic breast carcinoma in effusion cytology specimens. METHODS: In total, 91 cell blocks of malignant effusion specimens, including 47 metastatic breast carcinomas (nine triple-negative breast carcinomas [TNBCs] and 38 non-TNBCs) and 44 nonmammary malignancies, were selected for TRPS1 and GATA3 immunohistochemistry. Modified H scores ≥ 200 were considered positive staining. RESULTS: The positive rate of TRPS1 was similar between TNBC and non-TNBC (77.8% vs 73.3%, p = .802), whereas the positive rate of GATA3 was lower in TNBC than in non-TNBC (66.7% vs 89.5%, p = .087). The positive rate of TRPS1 was significantly higher in breast carcinoma than in urothelial carcinoma (74.5% vs 0%, p < .001), whereas the positive rate of GATA3 showed no difference between these two (85.1% vs 85.7%, p = .956). Notably, diffuse and strong aberrant expression of TRPS1 was observed in one lung adenocarcinoma and one serous adenocarcinoma in this series. The overall sensitivity, specificity, positive predictive value, and negative predictive value of TRPS1 immunohistochemistry for breast carcinoma were 74.5%, 95.5%, 94.6%, and 77.8%, respectively. CONCLUSION: TRPS1 is a sensitive and specific marker for metastatic breast cancer in serous effusion cell-block specimens. It shows superior sensitivity and specificity compared with GATA3, especially in the TNBC setting and for excluding urothelial carcinoma.

Cytologic features of a pleural effusion after silicone breast implant rupture.

Pleural effusion is an extremely rare complication of ruptured breast silicone implants. Rupture may be related to a recent trauma or occur spontaneously, making its diagnosis more difficult. In the few reported cases, cytology did not play a relevant role in its diagnosis. We describe and illustrate a silicone foreign body reaction in a pleural effusion. Cytologic findings were so remarkable as to permit a specific diagnosis. The patient, a 37-year-old female with a history of previous bilateral breast implant surgery was admitted because of a pleural effusion. Computed tomography scan showed a left effusion with secondary atelectasis and bilateral breast rupture with lymph node "siliconomas." Cytologic analysis of the effusion showed well-defined droplets or globules of transparent material, in addition to a microvacuolized background. Where abundant silicone droplets induced a staining artifact of the smears. These were cellular with numerous macrophages containing large vacuoles displacing the nuclei to the periphery. Some had a signet cell ring appearance, while others showed multinucleation. Flow cytometry revealed a predominant macrophagic cell population. With the increasing use of silicone breast implants, rare complications such as pleural effusion may become more common. The pathologist must consider this possibility when extracellular transparent droplets or evidence of a foreign body-type reaction are present. The artifact appearance of the smears may help to suspect it. This rare complication must be always considered when evaluating effusions in patients with silicone breast implants.

Pleural metastasis from parotid secretory carcinoma: First report of morphology on effusion cytology, and role of pan-TRK immunohistochemistry.

Distant metastasis from salivary gland secretory carcinoma (SC) is rare, with lung and pleura being the most frequent site. While cytological features of SC on fine needle aspirates are well documented, its morphology in serous effusions has not been described. We describe the cytomorphological features on effusion cytology of two patients with ETV6::NTRK3 fusion-positive SC, who subsequently developed pleural metastases. Cytospin preparations of pleural fluid showed tightly cohesive, irregularly shaped and ball-like clusters of large tumor cells with scant to abundant uni- and multi-vacuolated cytoplasm. Nuclei were eccentrically placed, round to oval, vesicular, with finely granular chromatin, irregular nuclear membranes and conspicuous to prominent nucleoli. With these features, the tumors resembled an adenocarcinoma, indistinguishable from a lung primary. Cell blocks from both cases showed tumor fragments, some of which had the hollow appearance of transversely sectioned cell spheres as seen in lung and breast adenocarcinomas. Immunohistochemistry on cell blocks revealed nuclear pan-TRK positivity in both cases. Case 1 also showed focal mammaglobin staining, and TTF1 negativity. Pleural metastases from SC may mimic other adenocarcinomas. As targeted therapy, that is, selective TRK inhibitors are available for treatment of metastatic disease, NTRK3 fusion status is not only diagnostic, but also required to plan treatment. Pan-TRK immunohistochemistry serves as a viable cost-effective, easy to apply surrogate marker for NTRK3 fusion, particularly in diagnostic laboratories lacking easy access to molecular testing on cytological material.

Diagnosis of Metastatic Carcinoma Using Body Cavity Fluid Specimens: A Comparison of Diagnostic Panels.

INTRODUCTION: Body cavity effusions are routinely used as cytologic specimens. The distinction between metastatic carcinoma, mesothelioma, and reactive mesothelial cells remains a major challenge. Immunohistochemistry (IHC) is a supplemental method that can aid in diagnosis and often involves many markers as part of an IHC panel. Several immunohistochemical markers are now widely used. This study aims to determine the optimal immunomarkers and IHC panels to differentiate reactive mesothelial cells from metastatic cancer in body cavity fluid samples. METHODS: IHC was performed for claudin-4, MOC-31, Ber-Ep4, D2-40, and calretinin on sections derived from 152 cellblocks containing effusions. The samples consisted of 16 (10.53%) benign and 136 (89.47%) malignant tumors, including 87 (63.97%) lung cancers, nine (6.62%) breast cancers, 11 (8.09%) gynecologic cancers, seven (5.15%) pancreaticobiliary cancers, and 22 (16.17%) unspecified primary malignancies. RESULTS: Claudin-4, MOC-31, Ber-EP4, D2-40, and calretinin demonstrated sensitivities of 91.18%, 91.91%, 55.88%, 90.44%, and 98.53%, respectively. The corresponding specificities were 100.00%, 100.00%, 100.00%, 93.75%, and 100.00%. The sensitivity and specificity were both 100% when claudin-4 or MOC-31 was combined with calretinin. The combination of four markers as an IHC panel (claudin-4, MOC-31, calretinin, and D2-40) had a sensitivity of 97.79% and a specificity of 100.00%. CONCLUSION: Claudin-4 and MOC-31 both demonstrated significant diagnostic value in distinguishing metastatic epithelial carcinoma from reactive mesothelium. The sensitivity, specificity, and accuracy of these two markers, one of which is an epithelial marker and one of which is a mesothelial marker, reached 100%. Therefore, a combination of these two markers may be appropriate.

Utility of the Ratio between Lactate Dehydrogenase (LDH) Activity and Total Nucleated Cell Counts in Effusions (LDH/TNCC Ratio) for the Diagnosis of Feline Infectious Peritonitis (FIP).

BACKGROUND: We tested the hypothesis that the ratio between lactate dehydrogenase activity (LDH) and total nucleated cell counts (TNCC) in effusions may be useful to diagnose feline infectious peritonitis (FIP). METHODS: LDH/TNCC ratio was retrospectively evaluated in 648 effusions grouped based on cytology and physicochemical analysis (step 1), on the probability of FIP estimated by additional tests on fluids (step 2) or on other biological samples (step 3, n = 471). Results of different steps were statistically compared. Receiver Operating Characteristic (ROC) curves were designed to assess whether the ratio identify the samples with FIP "probable/almost confirmed". The cut-offs with the highest positive likelihood ratio (LR+) or Youden Index (YI) or with equal sensitivity and specificity were determined. RESULTS: A high median LDH/TNCC ratio was found in FIP effusions (step1: 2.01) and with probable or almost confirmed FIP (step 2: 1.99; 2.20 respectively; step 3: 1.26; 2.30 respectively). The optimal cut-offs were 7.54 (LR+ 6.58), 0.62 (IY 0.67, sensitivity: 89.1%; specificity 77.7%), 0.72 (sensitivity and specificity: 79.2%) in step 2 and 2.27 (LR+ 10.39), 0.62 (IY 0.65, sensitivity: 82.1%; specificity 83.0%), 0.54 (sensitivity: 82.1%; specificity 81.9%) in step 3. CONCLUSIONS: a high LDH/TNCC ratio support a FIP diagnosis.

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

INTRODUCTION: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Diagnostic Value of Claudin-4 and EZH2 Immunohistochemistry in Effusion Cytology.

BACKGROUND: Metastatic adenocarcinoma (MAC) accounts for most cases of malignant effusions. Sometimes, it can be difficult to distinguish MAC from reactive mesothelial cells (RMC) in cytologic specimens. Our aim was to assess the diagnostic performance of a novel immunohistochemical panel composed of claudin-4 and EZH2 in differentiating MAC from RMC in effusion cytology. METHODS: A total of 80 cases of serous effusions (48 MAC and 32 RMC) were included. Immunohistochemistry using claudin-4 and EZH2 was performed on cell block sections of these cases. Assessment of staining patterns, intensity and percentage of target cells stained was done. RESULTS: Claudin-4 showed membranous staining in 46/48 of MAC and 1/32 of RMC. High EZH2 (≥ 50% of target cells) was detected in 42/48 MAC and 2/32 RMC. For the discrimination between MAC and RMC, claudin-4 exhibited 95.8% sensitivity and 96.9% specificity, high-EZH2 exhibited 87.5% sensitivity and 93.8% specificity, while the combination of both claudin-4 and high EZH2 showed 100% sensitivity and 90.6% specificity. CONCLUSION: Claudin-4 shows high sensitivity and specificity in differentiation between MAC and RMC in effusion cytology, and might be useful as a solitary marker for MAC. Adding EZH2 to claudin-4 increases the sensitivity to 100%. However, the interpretation of EZH2 results can be challenging due to its focal expression in RMC and inflammatory cells.

Effusion fluid cytology and COVID-19 infection.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is responsible for coronavirus disease 2019 (COVID-19), is known to cause severe respiratory infections with occasional accompanying pleural effusion (PE), pericardial effusion (PCE), or peritoneal effusion (PTE). The effect of COVID-19 on effusion cytology is not yet known. This study aimed to examine the cytomorphologic features and workup of effusion fluids in patients with active COVID-19 infection versus those in recovery. METHODS: PE (n = 15), PCE (n = 1), and PTE samples (n = 20) from hospitalized patients with a SARS-CoV-2 infection (from June 1, 2020, to December 30, 2020) were reviewed. Effusion fluids with metastatic carcinoma were excluded. Differential cell counts, cytomorphology, and relevant immunostains for effusion fluids were retrospectively evaluated and compared between patients with active infection (positive on a SARS-CoV-2 nucleic acid amplification test [NAAT] within 2 months; n = 23) and those in the recovery phase from COVID-19 (negative on a SARS-CoV-2 NAAT for >2 months; n = 13). RESULTS: The cytology diagnoses were negative for malignancy (n = 31), atypical (n = 4), and suspicious for malignancy (n = 1). Active infection cases showed more atypical mesothelial cells than recovery cases (P < .05); some had enlarged nuclei, prominent nucleoli, occasional multinucleation, and bizarre nuclei. Immunostains were performed more often in active infection cases than recovery cases (47.8% vs 7.7%; P < .05). Differential cell counts (available for 28 cases) showed no significant differences between the active infection and recovery groups. CONCLUSIONS: This study found atypical and bizarre mesothelial cells more often in effusions of cases with active COVID-19 infection in comparison with patients in recovery. It is important for cytopathologists to become familiar with the cytomorphologic effects of SARS-CoV-2 on effusion cytology so that these cases can be properly triaged.