Tongue Metastasis From Pleural Mesothelioma.

This case report describes a 62-year-old nonsmoking man with multiple pleural thickenings and a marked effusion.

Endobronchial solitary fibrous tumors: An enigma for diagnosis.

Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms constituting less than 2% of all soft tissue tumors. They typically originate in the thoracic cavity, mainly in the pleura, but can also occur in other various sites such as lung parenchyma, pericardium, and bronchus. In this study, a 49-year-old non-smoking female with a history of allergies presented to our pulmonary clinic with a chronic cough. An explorative bronchoscopy revealed an intrabronchial mass in the left superior bronchi, and a 68 Ga-DOTATOC positron emission computed tomography suggested a carcinoid tumor. Subsequent pulmonary segmentectomy unveiled a well-circumscribed polypoid lesion diagnosed as a low-grade bronchus SFT through histopathological and immunohistochemical assessments. The patient was asymptomatic after surgical excision and showed no other lesion during the 6-month follow-up. The endobronchial location of SFT is uncommon, with only a few reported cases in the literature, underscoring the necessity of considering various differential diagnoses, including carcinoid, mucoepidermoid carcinoma, endobronchial pleomorphic adenoma, hamartoma, leiomyoma, and metastasis, depending on location and imaging features. This report underscores the importance of careful histological and immunohistochemical evaluation in understanding and appropriately stratifying the risk associated with polypoid lesions.

Exploring the pathologist's role in understanding COVID-19: from pneumonia to long-COVID lung sequelae.

The crucial role of pathologists in enhancing our understanding of SARS-CoV-2-related disease, from initial pneumonia manifestations to persistent long COVID lung symptoms, is the focus of this review. Pathological explorations have offered unprecedented insights into the early stages of severe COVID-19, shedding light on the interplay between the virus and subsequent complications, thereby shaping clinical approaches. Growing interest is directed to residual lung abnormalities of COVID-19 survivors. Although various radiological studies reported long-lasting pulmonary changes (e.g., ground glass opacities, reticulations, and bronchiectasis), the true incidence of pulmonary fibrosis and corresponding pathological findings in these patients remains largely unknown. There are a few high-impact and knowledgeable works on late complications in COVID-19 survivors, several coming from explant or autopsy cases, and rare cases from in vivo sampling. The study of biopsy samples has further deepened our knowledge of the aftermath of COVID-19 on lung tissue, uncovering alterations at the cellular level and shifts in vascular and epithelial dynamics. Despite the substantial progress made, future research is needed to devise a uniform strategy for interpreting lung biopsies, with a focus on leveraging advanced tools such as molecular and digital pathology techniques, along with artificial intelligence.

Intrathymic Localization of Melanoma: A Brief Report of Two Cases and a Review of the Literature.

Intrathymic localizations of melanoma represent a very rare entity, with fewer than ten cases of intrathymic melanoma described in the literature. Herein, we describe two cases of patients who underwent surgical removal of a thymic mass at our thoracic surgery department between 2015 and 2022. The final pathological examination revealed a malignant melanoma in both cases; we therefore carried out a literature review to identify such rare and similar cases. In the first case, the intrathymic localization of melanoma was the first manifestation of the disease, posing a dilemma regarding the metastatic and primitive nature of the neoplasm. The second case described a thymic metastasis from a known previous cutaneous melanoma, for which the patient had successfully been treated six years earlier. After carefully reviewing the literature, we identified only six cases of verified primary intrathymic melanomas and one case of intrathymic metastasis resulting from melanoma previously described. Pathologists should be aware of the occurrence of this rare entity and mindful of the differential diagnoses. Several tools, including immunostaining of melanocytic markers and molecular investigations, are mandatory for final pathological diagnosis.

The significance of co-mutations in EGFR-mutated non-small cell lung cancer: Optimizing the efficacy of targeted therapies?

Non-small cell lung cancer (NSCLC) is the most common cause of cancer death worldwide. In non-squamous NSCLC, the identification of oncogenic drivers and the development of target-specific molecules led to remarkable progress in therapeutic strategies and overall survival over the last decade. Nevertheless, responses are limited by systematically acquired mechanisms of resistance early on after starting a targeted therapy. Moreover, mounting evidence has demonstrated that each oncogenic-driven cluster is actually heterogeneous in terms of molecular features, clinical behaviour, and sensitivity to targeted therapy. In this review, we aimed to examine the prognostic and predictive significance of oncogene-driven co-mutations, focusing mainly on EGFR and TP53. A narrative review was performed by searching MEDLINE databases for English articles published over the last decade (from January 2012 until November 2022). The bibliographies of key references were manually reviewed to select those eligible for the topic. The genetic landscape of EGFR-mutated NSCLC is more complicated than what is known so far. In particular, the occurrence of TP53 co-mutations stratify patients carrying EGFR mutations in terms of treatment response. The study provides a deeper understanding of the mechanisms underlying the variability of the genetic landscape of EGFR-mutated NSCLC and summarizes notably the clinical importance of TP53 co-mutations for an open avenue to more properly addressing the clinical decision-making in the near future.

Vascular/epithelial changes as late sequelae after recovery from SARS-COV-2 infection: an in-vivo comparative study.

AIMS: While there is partial evidence of lung lesions in patients suffering from long COVID there are substantial concerns about lung remodelling sequelae after COVID-19 pneumonia. The aim of the present retrospective comparative study was to ascertain morphological features in lung samples from patients undergoing tumour resection several months after SARS-CoV-2 infection. METHODS AND RESULTS: The severity of several lesions with a major focus on the vascular bed was analysed in 2 tumour-distant lung fragments of 41 cases: 21 SARS-CoV-2 (+) lung tumour (LT) patients and 20 SARS-CoV-2 (-) LT patients. A systematic evaluation of several lesions was carried out by combining their scores into a grade of I-III. Tissue SARS-CoV-2 genomic/subgenomic transcripts were also investigated. Morphological findings were compared with clinical, laboratory and radiological data. SARS-CoV-2 (+) LT patients with previous pneumonia showed more severe parenchymal and vascular lesions than those found in SARS-CoV-2 (+) LT patients without pneumonia and SARS-CoV-2 (-) LT patients, mainly when combined scores were used. SARS-CoV-2 viral transcripts were not detected in any sample. SARS-CoV-2 (+) LT patients with pneumonia showed a significantly higher radiological global injury score. No other associations were found between morphological lesions and clinical data. CONCLUSIONS: To our knowledge, this is the first study that, after a granular evaluation of tissue parameters, detected several changes in lungs from patients undergoing tumour resection after SARS-CoV-2 infection. These lesions, in particular vascular remodelling, could have an important impact overall on the future management of these frail patients.

Molecular Profiling of Tissue Samples with Chronic Rejection from Patients with Chronic Lung Allograft Dysfunction: A Pilot Study in Cystic Fibrosis Patients.

Chronic rejection (CR) is the main culprit for reduced survival and quality of life in patients undergoing lung transplantation (Ltx). High-throughput approaches have been used to unveil the molecular pathways of CR, mainly in the blood and/or in bronchoalveolar lavage. We hypothesized that a distinct molecular signature characterizes the biopsies of recipients with clinically confirmed histological signs of CR. Eighteen cystic fibrosis patients were included in the study and RNA sequencing was performed in 35 scheduled transbronchial biopsies (TBBs): 5 with acute cellular rejection, 9 with CR, and 13 without any sign of post-LTx complication at the time of biopsy; 8 donor lung samples were used as controls. Three networks with 33, 26, and 36 differentially expressed genes (DEGs) were found in TBBs with CR. Among these, seven genes were common to the identified pathways and possibly linked to CR and five of them (LCN2, CCL11, CX3CL1, CXCL12, MUC4) were confirmed by real-time PCR. Immunohistochemistry was significant for LCN2 and MUC4. This study identified a typical gene expression pattern in TBBs with histological signs of CR and the LCN2 gene appeared to play a central role. Thus, it could be crucial in CR pathophysiology.

Evaluation of Tissue Ischemia/Reperfusion Injury in Lung Recipients Supported by Intraoperative Extracorporeal Membrane Oxygenation: A Single-Center Pilot Study.

Intraoperative veno-arterial (VA) extracorporeal membrane oxygenation (ECMO) as intraoperative hemodynamic support during lung transplantation is becoming a standard practice due to promising clinical results. Nevertheless, studies on tissue/molecular pathways investigating ischemia/reperfusion injury are still lacking. Patients receiving a bilateral lung transplantation between January 2012 and December 2018 at the University Hospital of Padova were included in this retrospective single-center observational study. The present study aimed to investigate ischemia/reperfusion injury in 51 tissue specimens obtained from 13 recipients supported by intraoperative VA-ECMO and 38 who were not. Several tissue analyses, including apoptosis evaluation and inducible nitric oxide synthase expression, were performed on the biopsies at the time of transplantation. Lung samples from the ECMO group (both pre- and post-reperfusion) were comparable, or for some parameters better, than samples from the non-ECMO group. Leukocyte margination was significantly lower in the ECMO group than in the non-ECMO group. Primary graft dysfunction, mainly at 24 and 48 h, was correlated with the tissue injury score of the post-reperfusion biopsy. The interquartile ranges for all morphological parameters showed high grade variability between pre- and post-reperfusion in the non-ECMO group. These preliminary data support the use of intraoperative ECMO based on lower lung tissue ischemia/reperfusion injury. Larger case series are mandatory to confirm our findings.

Case report: Mesothelioma and BAP1 tumor predisposition syndrome: Implications for public health.

BRCA-1 associated protein 1 (BAP1) tumour predisposition syndrome (TPDS) is a hereditary condition characterised by germline mutation of the tumour suppressor BAP1. This disorder is associated with the development of various benign and malignant tumours, mainly involving the skin, eyes, kidneys, and mesothelium. In this article, we report the case of a man recruited through the Apulia (Southern Italy) Mesothelioma Regional Operational Centre of the National Register of Mesotheliomas, who suffered from uveal melanoma, renal cancer, and mesothelioma, and a familial cluster of BAP1 germline mutations demonstrated by molecular analyses. The family members of the proband developed multiple malignancies. As tumours arising in this context have specific peculiarities in terms of clinical behaviour, identification of this condition through appropriate genetic counselling should be considered for adequate primary, secondary, and tertiary prevention measures for offspring.

Multidrug-Resistant and Extended-Spectrum ß-Lactamase Gram-Negative Bacteria in Bilateral Lung Transplant Recipients: Incidence, Risk Factors, and In-Hospital Mortality.

BACKGROUND: In recent decades, the incidence of multidrug-resistant (MDR) and extended-spectrum ß-lactamase (ESBL) gram-negative (GN) bacteria has increased progressively among lung transplantation (LT) recipients. A prompt diagnosis, prevention, and management of these pathogens remain the cornerstone for successful organ transplantation. RESEARCH QUESTION: What are the incidence of MDR and ESBL GN bacteria within the first 30 days after LT and related risk of in-hospital mortality? What are the potential clinical predictors of isolation of MDR and ESBL GN bacteria? STUDY DESIGN AND METHODS: All consecutive LT recipients admitted to the ICU of the University Hospital of Padua (February 2016-December 2021) were screened retrospectively. Only adult patients undergoing the first bilateral LT and not requiring invasive mechanical ventilation, extracorporeal membrane oxygenation, or both before surgery were included. MDR and ESBL GN bacteria were identified using in vitro susceptibility tests and were isolated from the respiratory tract, blood, urine, rectal swab, or surgical wound or drainage according to a routine protocol. RESULTS: One hundred fifty-three LT recipients were screened, and 132 were considered for analysis. Median age was 52 years (interquartile range, 41-60 years) and 46 patients (35%) were women. MDR and ESBL GN bacteria were identified in 45 patients (34%), and 60% of patients demonstrated clinically relevant infection. Pseudomonas aeruginosa (n = 22 [49%]) and Klebsiella pneumoniae (n = 17 [38%]) were frequently isolated after LT from the respiratory tract (n = 21 [47%]) and multiple sites (n = 18 [40%]). Previous recipient-related colonization (hazard ratio [HR], 2.48 [95% CI, 1.04-5.90]; P = .04) and empirical exposure to broad-spectrum antibiotics (HR, 6.94 [95% CI, 2.93-16.46]; P < .01) were independent predictors of isolation of MDR and ESBL GN bacteria. In-hospital mortality of the MDR and ESBL group was 27% (HR, 6.38 [95% CI, 1.98-20.63]; P < .01). INTERPRETATION: The incidence of MDR and ESBL GN bacteria after LT was 34%, and in-hospital mortality was six times greater. Previous recipient-related colonization and empirical exposure to broad-spectrum antibiotics were clinical predictors of isolation of MDR and ESBL GN bacteria.

Tumor Immune-Infiltrate Landscape After Chemo-Radiotherapy in a Case Series of Patients with Non-small Cell Lung Cancer: Pretreatment Predictors and Correlation With Outcome.

INTRODUCTION: Data on tumor immune-milieu after chemo-radiation (CT-RT) are scarce. Noninvasive tools are needed to improve the treatment of non-small cell lung cancer (NSCLC), especially in the locally advanced (LA) setting. METHODS: We collected a series of superior-sulcus (SS)- patients with NSCLC referred to our Institute (2015-2019), eligible for a preoperative CT-RT. We characterized tumor-infiltrating immune cells (TIICs), determined PD-L1-TPS and the residual viable tumor cells (RVTC). Radiological and metabolic responses were reviewed. We calculated pre-surgery neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR). RESULTS: Eight patients were included. Radiological responses were 6 disease stabilities (SD) and 2 partial responses (PR). Metabolic responses were 4 SD and 4 PR. CD68+-TIICs were correlated with metabolic response and lower RVTC. CD68+-TIICs were associated with higher PLR. Higher PLR values seemed linked with lower RVTC. CONCLUSIONS: These preliminary results could be useful for consolidation treatment selection for patients with LA-NSCLC without evaluable baseline PD-L1 and higher PLR values.

Morphologic-Molecular Transformation of Oncogene Addicted Non-Small Cell Lung Cancer.

Patients with non-small cell lung cancer, especially adenocarcinomas, harbour at least one oncogenic driver mutation that can potentially be a target for therapy. Treatments of these oncogene-addicted tumours, such as the use of tyrosine kinase inhibitors (TKIs) of mutated epidermal growth factor receptor, have dramatically improved the outcome of patients. However, some patients may acquire resistance to treatment early on after starting a targeted therapy. Transformations to other histotypes-small cell lung carcinoma, large cell neuroendocrine carcinoma, squamous cell carcinoma, and sarcomatoid carcinoma-have been increasingly recognised as important mechanisms of resistance and are increasingly becoming a topic of interest for all specialists involved in the diagnosis, management, and care of these patients. This article, after examining the most used TKI agents and their main biological activities, discusses histological and molecular transformations with an up-to-date review of all previous cases published in the field. Liquid biopsy and future research directions are also briefly discussed to offer the reader a complete and up-to-date overview of the topic.

Multi-Design Differential Expression Profiling of COVID-19 Lung Autopsy Specimens Reveals Significantly Deregulated Inflammatory Pathways and SFTPC Impaired Transcription.

The transcriptomic profiling of lung damage associated with SARS-CoV-2 infection may lead to the development of effective therapies to prevent COVID-19-related deaths. We selected a series of 21 autoptic lung samples, 14 of which had positive nasopharyngeal swabs for SARS-CoV-2 and a clinical diagnosis of COVID-19-related death; their pulmonary viral load was quantified with a specific probe for SARS-CoV-2. The remaining seven cases had no documented respiratory disease and were used as controls. RNA from formalin-fixed paraffin-embedded (FFPE) tissue samples was extracted to perform gene expression profiling by means of targeted (Nanostring) and comprehensive RNA-Seq. Two differential expression designs were carried out leading to relevant results in terms of deregulation. SARS-CoV-2 positive specimens presented a significant overexpression in genes of the type I interferon signaling pathway (IFIT1, OAS1, ISG15 and RSAD2), complement activation (C2 and CFB), macrophage polarization (PKM, SIGLEC1, CD163 and MS4A4A) and Cathepsin C (CTSC). CD163, Siglec-1 and Cathepsin C overexpression was validated by immunohistochemistry. SFTPC, the encoding gene for pulmonary-associated surfactant protein C, emerged as a key identifier of COVID-19 patients with high viral load. This study successfully recognized SARS-CoV-2 specific immune signatures in lung samples and highlighted new potential therapeutic targets. A better understanding of the immunopathogenic mechanisms of SARS-CoV-2 induced lung damage is required to develop effective individualized pharmacological strategies.

RNA Sequencing of Epithelial Cell/Fibroblastic Foci Sandwich in Idiopathic Pulmonary Fibrosis: New Insights on the Signaling Pathway.

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease characterized by irreversible scarring of the distal lung. IPF is best described by its histopathological pattern of usual interstitial pneumonia (UIP), characterized by spatial heterogeneity with alternating interstitial fibrosis and areas of normal lung, and temporal heterogeneity of fibrosis characterized by scattered fibroblastic foci (FF), dense acellular collagen and honeycomb changes. FF, comprising aggregated fibroblasts/myofibroblasts surrounded by metaplastic epithelial cells (EC), are the cardinal pathological lesion and their presence strongly correlates with disease progression and mortality. We hypothesized that the EC/FF sandwich from patients with UIP/IPF has a distinct molecular signature which could offer new insights into the crosstalk of these two crucial actors in the disease. Laser capture microdissection with RNAseq was used to investigate the transcriptome of the EC/FF sandwich from IPF patients versus controls (primary spontaneous pneumothorax). Differentially expressed gene analysis identified 23 up-regulated genes mainly related to epithelial dysfunction. Gene ontology analysis highlighted the activation of different pathways, mainly related to EC, immune response and programmed cell death. This study provides novel insights into the IPF pathogenetic pathways and suggests that targeting some of these up-regulated pathways (particularly those related to secreto-protein/mucin dysfunction) may be beneficial in IPF. Further studies in a larger number of lung samples, ideally from patients with early and advanced disease, are needed to validate these findings.

Mesothelioma and Colorectal Cancer: Report of Four Cases with Synchronous and Metachronous Presentation.

There is evidence that asbestos could play a role in the carcinogenesis of digestive cancers. The presence of asbestos fibres in histological samples from gastric, biliary, colon cancers has been reported, but the mechanism is still controversial. It has been hypothesised that asbestos reaches these sites, especially through contaminated water; however, some experimental studies have shown that the inhaled fibres are mobile, so they can migrate to many organs, directly or via blood and lymph flow. We report four unusual cases of colorectal cancers in patients with a long history of asbestos exposure who also developed synchronous or metachronous mesothelioma. We evaluated the roles of BRCA associated protein-1 (BAP1) and cyclin-dependent kinase inhibitor 2A (CDKN2A) in colon cancer and mesothelioma to support the hypothesis that BAP-1 and CDKN2A are tumour suppressor genes involved in disease progression, recurrence, or death in both digestive cancers and mesothelioma. Potentially, these markers may be used as predictors of worse prognosis, but we also stress the importance of clinical surveillance of exposed patients because asbestos could induce cancer in any organ.

Molecular Pathways in Peritoneal Mesothelioma: A Minireview of New Insights.

Mesothelioma is a rare malignant neoplasm with poor survival. It mainly affects the pleura (90%) but can arise in all serous cavities: peritoneum (5-10%), pericardium and tunica vaginalis testis (<1%). The onset of pleural mesothelioma is strictly related to asbestos exposure with a long latency time. The causal link with asbestos has also been suggested for peritoneal mesothelioma, while the importance of exposure in the onset of pericardial and tunica vaginalis testis mesotheliomas is not well known. Mesothelioma remains an aggressive and fatal disease with a five-year mortality rate higher than 95%. However, new therapeutic approaches based on molecular-targeted and immunomodulatory therapies are being explored but have conflicting results. In this context, the identification of critical targets appears mandatory. Awareness of the molecular and physiological changes leading to the neoplastic degeneration of mesothelial cells and the identification of gene mutations, epigenetic alterations, gene expression profiles and altered pathways could be helpful for selecting targetable mechanisms and molecules. In this review, we aimed to report recent research in the last 20 years focusing on the molecular pathways and prognostic factors in peritoneal mesothelioma and their possible diagnostic and therapeutic implications.

Automated Analysis of Proliferating Cells Spatial Organisation Predicts Prognosis in Lung Neuroendocrine Neoplasms.

Lung neuroendocrine neoplasms (lung NENs) are categorised by morphology, defining a classification sometimes unable to reflect ultimate clinical outcome. Subjectivity and poor reproducibility characterise diagnosis and prognosis assessment of all NENs. Here, we propose a machine learning framework for tumour prognosis assessment based on a quantitative, automated and repeatable evaluation of the spatial distribution of cells immunohistochemically positive for the proliferation marker Ki-67, performed on the entire extent of high-resolution whole slide images. Combining features from the fields of graph theory, fractality analysis, stochastic geometry and information theory, we describe the topology of replicating cells and predict prognosis in a histology-independent way. We demonstrate how our approach outperforms the well-recognised prognostic role of Ki-67 Labelling Index on a multi-centre dataset comprising the most controversial lung NENs. Moreover, we show that our system identifies arrangement patterns in the cells positive for Ki-67 that appear independently of tumour subtyping. Strikingly, the subset of these features whose presence is also independent of the value of the Labelling Index and the density of Ki-67-positive cells prove to be especially relevant in discerning prognostic classes. These findings disclose a possible path for the future of grading and classification of NENs.

The Rarest of Rare Thymic Lesions: A 10-Year Surgical Pathology Experience.

The thymus is a specialized primary lymphoid organ located in the midline pre-vascular mediastinum. The organ is the site of various pathological processes, neoplastic and not, whose rarity has not allowed in-depth studies on clinical or histological features of rarest and unusual variants. Herein, we report a 10-year Padova experience in the surgical pathology of the thymus, focusing on the pathological description of nonneoplastic lesions and rare epithelial and mesenchymal tumors recorded in our database, which comprises over 600 thymectomies. The extrapolated rare cases have been categorized into four groups that included 15 cysts, 18 carcinomas, 5 neuroendocrine tumors, and 2 soft tissue tumors. The cases are described from a clinical and pathological point of view and discussed in dedicated sections with a review of the most important literature. In this case, review series, we aim to update the epidemiology of these rare entities, improve diagnostic awareness, and finally, promote a collaborative network between referral centers.

Evaluation of prognostic histological parameters proposed for pleural mesothelioma in diffuse malignant peritoneal mesothelioma. A short report.

INTRODUCTION: Diffuse malignant peritoneal mesothelioma (DMPM) is a rare malignant neoplasm with poor survival that shares some similarities with the best-known pleural variant, pleural mesothelioma. The recent European Reference Network on Rare Adult Cancers (EURACAN)/International Association for the Study of Lung Cancer (IASLC) proposals attempted to improve the histological diagnosis and patient risk stratification. Herein, we investigated whether the pathology recommendations and suggestions of the pleural proposals were applicable to diffuse malignant peritoneal mesothelioma. METHODS: Fifty multiple laparoscopic biopsies of DMPM were consecutively collected at the Pathology Unit of the University of Bari. A two-tier system, i.e., low, and high grade, was used to categorize 34 epithelioid DMPMs. Architectural patterns, cytological features and stromal changes were also reported. Immunohistochemistry was performed for BRCA1-associated protein 1 (BAP1), programmed death-ligand 1 (PD-L1), and Ki67, while fluorescence in situ hybridization (FISH) was performed for p16/cyclin-dependent kinase inhibitor 2A (CDKN2A). RESULTS: High-grade epithelioid mesothelioma, high Ki67, and p16/CDKN2A deletion were significantly associated with short survival (p = 0.004, p < 0.0001, and p = 0.002, respectively). BAP1 loss and PD-L1 negativity were the most common findings. Multivariate analysis revealed that the nuclear grading system and p16 deletion significantly correlated with survival (p = 0.003 each). CONCLUSIONS: The present study examined the prognostic significance of several factors proposed for pleural mesothelioma in an extra pleural site. Notably, the introduction of a grading system may provide better risk stratification in epithelioid DMPM. Ki67, BAP1 and p16/CDKN2A should also be measured whenever possible. A detailed report with all supportive data would allow us to collect sufficient information for use in further studies on larger case series.

Diagnostic Challenges in Epithelioid Pleural Mesothelioma: Case Series with Support from Electron Microscopy.

The histological diagnosis of pleural epithelioid mesothelioma can be difficult in the case of rare variants or in the definition of neoplasm origin in patients with previous or concomitant tumours. Currently, several immunohistochemical reactions are available in the surgical pathologist's armamentarium that allow us to obtain a more sensitive and specific diagnosis of malignant pleural mesothelioma. However, in some cases, the final interpretation remains inconclusive. Historically, ultrastructural examination has represented a useful tool for the definition of the mesothelial nature of neoplastic cells due to their peculiar morphological characteristics. The recent international guidelines for pathological diagnosis of pleural mesothelioma suggest the use of electron microscopy when the immunohistochemical reactions are equivocal or when further support of a diagnosis of mesothelioma is needed. This paper presents three cases of pleural epithelioid mesothelioma whose diagnoses were finally supported by ultrastructural examination.