Epithelioid Malignant Mesothelioma Research Articles

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

BackgroundMalignant pleural mesothelioma (MPM) poses diagnostic challenges due to its resemblance to benign pleural pathologies and different histological subtypes. Several immunohistochemistry markers have been employed to aid in accurate diagnosis. MethodsThe present systematic review and meta-analysis aimed to assess the diagnostic performance of various immunohistochemistry markers in malignant pleural mesothelioma diagnosis and its histological subtypes. Following the PRISMA guidelines, we systematically searched the literature for articles on using different immunohistochemical markers in MPM and its histological subtypes. EMBASE, LILACS, MEDLINE, and Virtual Health Library were searched for studies published up to August 2023. We used the QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies) criteria to assess the quality of the included articles. Meta-analyses were performed to determine prevalence using a random-effects model. Results103 studies met the inclusion criteria, comprising a diverse range of immunohistochemistry markers. EMA and desmin-loss exhibited high sensitivity (96% and 92%, respectively) in distinguishing malignant pleural mesothelioma from benign pleural pathologies. Specificity was notably high for both BAP1-loss and survivin expression at 100%. Subtype-specific analyses demonstrated that EMA and HEG1 were sensitive markers for epithelioid mesothelioma, while GLUT1 showed high sensitivity for sarcomatoid mesothelioma. In cases comparing epithelioid mesothelioma and lung adenocarcinoma, CAM5.2 and calretinin displayed high sensitivity, while WT1 and BAP1-loss demonstrated exceptional specificity for malignant epithelioid mesothelioma. In the case of sarcomatoid mesothelioma and sarcomatoid lung carcinoma, GATA3 exhibited the most heightened sensitivity, while GATA3 and D2–40 displayed the best specificity for sarcomatoid malignant mesothelioma diagnosis. ConclusionImmunohistochemistry markers are essential in accurately diagnosing malignant pleural mesothelioma and its histological subtypes. This systematic review and meta-analysis provide a comprehensive insight into the diagnostic performance of these markers, facilitating their potential clinical utility in the discrimination of malignant pleural mesothelioma from other pleural pathologies and the differentiation of malignant pleural mesothelioma subtypes.

Clinicopathological Impact of CPA4, UHRF1, Glypican-1, and CD90 Expression in Lung Adenocarcinoma and Epithelioid Malignant Mesothelioma

Clinicopathological Impact of CPA4, UHRF1, Glypican-1, and CD90 Expression in Lung Adenocarcinoma and Epithelioid Malignant Mesothelioma

Gastric carcinoma and peritoneal mesothelioma – a rare case of synchronous cancer. Clinical observation

Primary-multiple malignant neoplasms develop in about 9 % of cancer patients in the Russian Federation, while synchronous tumors are detected in a quarter of them, which dictates the need for a mandatory multidisciplinary approach to the choice of treatment. Localization of synchronous primary-multiple tumors in one anatomical zone requires a qualitative interpretation of instrumental diagnostic methods and morphological analysis after biopsy of each tumor. Along with this, there is a possibility of an erroneous opinion about the presence of different histological structures of the detected tumors and the data of visual assessment methods are interpreted in favor of a single disease.This paper presents a clinical observation of a rare combination of gastric adenocarcinoma and peritoneal mesothelioma. The case was discussed at a multidisciplinary consultation with the participation of a surgeon, a chemotherapist and a radiologist. Taking into account the clinical stage of gastric body cancer c T3N1M0, III stage, it was decided to conduct preoperative polychemotherapy at the first stage. Repeated diagnostic laparoscopy revealed no negative dynamics, multiple small dropouts in the peritoneum persisted. Subsequently, the operation was performed in the volume of gastrectomy, total parietal peritectomy and appendectomy without macroscopic signs of a residual tumor. It was decided to refrain from intra-abdominal chemoperfusion with hyperthermia due to the large volume of surgery and the previous 8 courses of polychemotherapy. Microscopic examination of the altered part of the stomach wall revealed residual adenocarcinoma (type according to Lauren – intestinal) with signs of therapeutic pathomorphosis G3 (according to Mandard), which had grown into the subserous layer and the fiber of the small omentum, with signs of perineural invasion, in the absence of vascular invasion; resection edges – R0. On the surface of the removed fragments of the peritoneum, various foci of malignant epithelioid mesothelioma were found. At the control examination a year later, according to computed tomography and esophagogastroduodenoscopy, there were no signs of progression, the patient’s condition was satisfactory.

Comprehensive epithelial biomarker analysis of malignant mesothelioma: EpCAM positivity is a potential diagnostic pitfall.

Epithelial cell adhesion molecule (EpCAM) is frequently used to distinguish carcinoma from background mesothelial cells during cytologic examination of body cavity fluids. Previously, the authors identified one malignant mesothelioma case with strong and diffuse membranous EpCAM staining, making it indistinguishable from carcinoma. In this study, the authors evaluated all available effusion specimens from patients with malignant mesothelioma, including the above-mentioned index case, obtained at Stanford Health Care, from 2011 to 2021 (N=17) as well as control cases (N=5). Analyses included an immunohistochemistry (IHC) assay for EpCAM and claudin-4, a multiplexed immunofluorescent (IF) assay for EpCAM, and an RNA in situ hybridization assay targeting EpCAM. The authors detected EpCAM positivity of variable intensity and percentage in four malignant mesothelioma cases (23.5%; although only two showed positivity for the epithelial-specific IHC marker MOC31 in ≥40% of cells) and claudin-4 negativity in all cases, with two cases displaying focal and weak claudin-4 staining in <1% of cells. Multiplexed IF staining on the cases with EpCAM IHC positivity showed strong, membranous EpCAM staining in one of four cases. RNA in situ hybridization also was used to assess the correlation between EpCAM positivity by IHC/IF and RNA expression levels. Strong EpCAM RNA expression was detected in the three malignant mesothelioma cases. The current findings revealed that a subset of epithelioid malignant mesothelioma cases mimic or exhibit the immunophenotypic features of carcinoma when evaluating for EpCAM only. Additional biomarker testing, such as claudin-4, may help avoid this potential pitfall to yield accurate diagnoses.

Highlighting the immunohistochemical differences of malignant mesothelioma subtypes via case presentations.

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

Safety and Feasibility of High-Pressure/High-Dose Pressurized Intraperitoneal Aerosol Chemotherapy (HP/HD-PIPAC) for Primary and Metastatic Peritoneal Surface Malignancies.

The aim of this study was to evaluate the feasibility and perioperative safety of high-pressure/high-dose pressurized intraperitoneal aerosol chemotherapy (HP/HD-PIPAC) to manage peritoneal surface malignancies (PSM). Retrospective analysis of a prospective database of about 130 consecutive patients scheduled for HP/HD-PIPACs for PSM. Doxorubicin plus cisplatin (PIPAC-C/D) or oxaliplatin (PIPAC-Ox) were nebulized into a constant capnoperitoneum of 20mmHg at doses of 6, 30, or 120mg/m2 of body surface area (BSA). Outcome criteria were perioperative complications (Clavien-Dindo). The median age of patients was 62 years (range 9-82), and the primary tumor site was of colorectal (CRC), upper gastrointestinal tract (UGI), unknown primary (CUP), malignant epithelioid mesothelioma of the peritoneum (MPM), hepato-pancreatic-biliary tract (HPB), and other origin in 30 (23.1%), 27 (20.8%), 16 (12.3%), 16 (12.3%), 6 (4.6%), and 35 (26.9%) patients, respectively. Abdominal access failed for a first, second, third, and fourth or more HP/HD-PIPAC in 12/130 (9.2%), 4/64 (6.3%), 6/40 (15.0%), and 2/33 (6.1%) patients. A total of 243 procedures were performed in 118 patients. No intraoperative complications related to increased capnoperitoneal pressure occurred, but an intraoperative bleeding complication was observed in 1/243 (0.4%) patients. The overall rate of postoperative procedure-related complications was 19.3% (47/243), while 15.3% (37/243), 1.6% (6/243), 1.6% (1/243), 0.4% (1/243), and 0.4% (1/243) were Grade I, II, III, IV, and V complications, respectively. Perioperative complications of HP/HD-PIPAC are comparable with standard pressure/dose PIPAC treatment protocols. Prospective studies are warranted to examine potential improvement in therapy outcomes.

RhoA and vigilin are candidates for immunohistochemical markers for epithelioid malignant mesothelioma

Diagnostic markers of malignant mesothelioma (MM) have been extensively investigated. Immunohistochemistry (IHC) markers, such as calretinin, have been used for pathologic diagnosis. However, more diagnostic markers are required to improve the specificity and sensitivity of pathologic diagnosis. This study proposed two proteins as diagnostic markers for epithelioid MM. One is RhoA, an MM mutation-susceptible locus-derived protein, and another is vigilin, a lung small cell carcinoma marker. IHC was performed using 93 MM (epithelioid, 71 cases; sarcomatoid, 13 cases; and biphasic, 9 cases), 64 lung adenocarcinoma (LAC), 60 lung squamous cell carcinoma (LSC), and 14 normal mesothelial (NM) tissues. The majority of epithelioid MM cases were positive for both RhoA and vigilin, whereas both IHCs showed lower stainability in biphasic and sarcomatoid MM. Besides, both IHCs showed significantly higher stainability for RhoA and vigilin in epithelioid MM than in LAC and LSC (p < 0.05). Chi-square tests showed that both RhoA and vigilin IHC positive rate in epithelioid MM was not significantly different from that of calretinin (p > 0.05). In the differential diagnosis of MM from lung cancer, the accuracy and specificity of RhoA, vigilin, and calretinin staining were almost equivalent. Further, H-score test showed that there was no significant difference between RhoA versus calretinin and vigilin versus calretinin in IHC positivity in epithelioid MM (p > 0.05). In conclusion, RhoA and vigilin may be candidates for immunohistochemical markers for epithelioid MM.

Combined treatment with inhibitors of ErbB Receptors and Hh signaling pathways is more effective than single treatment in reducing the growth of malignant mesothelioma both in vitro and in vivo

Malignant mesothelioma (MM) is a rare orphan aggressive neoplasia with low survival rates. Among the other signaling pathways, ErbB receptors and Hh signaling are deregulated in MM. Thus, molecules involved in these signaling pathways could be used for targeted therapy approaches. The aim of this study was to evaluate the effects of inhibitors of Hh- (GANT-61) and ErbB receptors (Afatinib)-mediated signaling pathways, when used alone or in combination, on growth, cell cycle, cell death and autophagy, modulation of molecules involved in transduction pathways, in three human MM cell lines of different histotypes. The efficacy of the combined treatment was also evaluated in a murine epithelioid MM cell line both in vitro and in vivo. This study demonstrated that combined treatment with two inhibitors counteracting the activation of two different signaling pathways involved in neoplastic transformation and progression, such as those activated by ErbB and Hh signaling, is more effective than the single treatments in reducing MM growth in vitro and in vivo. This study may have clinical implications for the development of targeted therapy approaches for MM.

OTHR-22. Malignant mesothelioma (MM) as second cancer in childhood brain tumor survivors: the first child with neurofibromatosis type 2 and concurrent MM

Abstract We report two cases of malignant mesothelioma (MM) in childhood brain tumor survivors. A 40-year-old man, who was treated at the age of ten with chemotherapy and craniospinal radiotherapy (up to 54.5 Gy) for a pineal secreting non-germinomatous germ cell tumor, had persistent fever, fatigue, and weight loss. A total body CT scan revealed several pulmonary and abdominal wall nodularities. The histological examination on a biopsy diagnosed a biphasic MM. The karyotype and array-CGH of peripheral blood were normal; a FISH of tumor cells showed a breakage of locus EWSR1 (22q12.2). In this case, environmental exposure was identified (asbestos in public water tanks). His MM followed an aggressive course and resulted in death after three months. A twelve-year-old boy affected by severe neurofibromatosis type 2 (NF2) already treated with several neurosurgical exeresis and chemotherapy lines (hydroxycarbamide, bevacizumab, sirolimus), developed multiple abdominal lesions, associated with pleural effusion and weight loss. The CT scan showed the thickening of the left pleura and multiple peritoneal nodules. The cytological examination on thoracentesis diagnosed an epithelioid MM. The karyotype on paracentesis-obtained cells revealed monosomy of chromosomes 14 and 22, loss of Y, and trisomy of 6, 10, 11, 16, and 20. NGS is currently ongoing to exclude germline or somatic second hits. Importantly, no exposure to asbestos was found. Less than 2% of MMs occur below 45 years of age; it is a rare secondary tumor in cancer survivors and environmental or genetic contributing causes are often detectable on a careful investigation. Variants in NF2 are considered to be the second most common after those in BAP1. To our knowledge, this is the first child with NF2 and concurrent MM reported to date. Compared to the expected prognosis, his MM has followed a mild course, and one year after diagnosis he is still alive.

Immunohistochemical Pitfalls in Malignant Peritoneal Mesothelioma: A Case Report and Review for the General Pathologist

Abstract Malignant peritoneal mesothelioma is an aggressive malignancy that often mimics carcinomatosis both clinically and histologically, making definitive diagnosis challenging for the general pathologist. Many of the common immunohistochemical stains used to narrow the differential diagnosis show a lack of specificity, requiring a panel approach to ensure correct categorization. We report a case of epithelioid malignant peritoneal mesothelioma with diffuse and strong Ber-EP4 positivity and review some of the most commonly encountered pitfalls associated with immunohistochemical staining.

Forchlorfenuron and Novel Analogs Cause Cytotoxic Effects in Untreated and Cisplatin-Resistant Malignant Mesothelioma-Derived Cells.

Malignant mesothelioma (MM) is a currently incurable, aggressive cancer derived from mesothelial cells, most often resulting from asbestos exposure. The current first-line treatment in unresectable MM is cisplatin/pemetrexed, which shows very little long-term effectiveness, necessitating research for novel therapeutic interventions. The existing chemotherapies often act on the cytoskeleton, including actin filaments and microtubules, but recent advances indicate the ‘fourth’ form consisting of the family of septins, representing a novel target. The septin inhibitor forchlorfenuron (FCF) and FCF analogs inhibit MM cell growth in vitro, but at concentrations which are too high for clinical applications. Based on the reported requirement of the chloride group in the 2-position of the pyridine ring of FCF for MM cell growth inhibition and cytotoxicity, we systematically investigated the importance (cell growth-inhibiting capacity) of the halogen atoms fluorine, chlorine, bromine and iodine in the 2- or 3-position of the pyridine ring. The MM cell lines ZL55, MSTO-211H, and SPC212, and—as a control—immortalized Met-5A mesothelial cells were used. The potency of the various halogen substitutions in FCF was mostly correlated with the atom size (covalent radius); the small fluoride analogs showed the least effect, while the largest one (iodide) most strongly decreased the MTT signals, in particular in MM cells derived from epithelioid MM. In the latter, the strongest effects in vitro were exerted by the 2-iodo and, unexpectedly, the 2-trifluoromethyl (2-CF3) FCF analogs, which were further tested in vivo in mice. However, FCF-2-I and, more strongly, FCF-2-CF3 caused rapidly occurring strong symptoms of systemic toxicity at doses lower than those previously obtained with FCF. Thus, we investigated the effectiveness of FCF (and selected analogs) in vitro in MM cells which were first exposed to cisplatin. The slowly appearing population of cisplatin-resistant cells was still susceptible to the growth-inhibiting/cytotoxic effect of FCF and its analogs, indicating that cisplatin and FCF target non-converging pathways in MM cells. Thus, a combination therapy of cisplatin and FCF (analogs) might represent a new avenue for the treatment of repopulating chemo-resistant MM cells in this currently untreatable cancer.

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.

Immunocytochemistry of effusion fluids: Introduction to SCIP approach.

Due to the remarkably wide morphologic spectrum of reactive mesothelial cells, some of the effusion fluids may be difficult to interpret with objective certainty by cytomorphology alone. Cytomorphology of well to moderately differentiated adenocarcinomas (responsible for the bulk of malignant effusions) may overlap with floridly reactive mesothelial cells. Even mesotheliomas including diffuse malignant epithelioid mesothelioma, are usually cytomorphologically bland without unequivocal features of malignancy.The intensity of challenge depends on the interpreter’s training or experience level, institutional demographics of patients (such as type of prevalent diseases, predominant sex and age group), technical support, and quality of cytopreparatory processing. In general immunocytochemistry is valuable adjunct to facilitate objective interpretation with or without other ancillary techniques as indicated. An increasing number of immunomarkers is further refining the contribution of immunohistochemistry to this field.However, application of immunohistochemistry to effusion fluids is relatively challenging because of many variables. Multiple factors such as delay after specimen collection, specimen processing related factors including fixation and storage; ambient conditions under which paraffin blocks are archived (for retrospective testing); antigen retrieval method; duration of antigen retrieval step; antibody clone and dilution; and antibody application time are identical to application of immunohistochemistry in other areas. The significant challenge related to the potential compromization of the immunoreactivity pattern due to exposure to non-formalin fixatives / reagents is also applicable to effusion fluid specimens.The immunoreactivity results would be compared and corelated with cumulative metadata based on the reported studies performed and validated on formalin-fixed paraffin-embedded tissue sections. Deviating from such protocols may lead to suboptimal results, which is not uncommon in clinical practice with potential compromization of patient care and related liability. Because of this, it is critical to perform immunocytochemistry on formalin-fixed cell-block sections only.In addition, unless the interpretation criteria for immunohistochemical evaluation of effusion fluids are not modified specifically, it may not be productive in resolving some challenging cases. However, this aspect is not well elaborated in the literature. A basic and critical challenge is finding and locating the cells of interest in cell-block sections of effusion fluids. A unique approach is to choose a fundamental immunopanel which highlight the mesothelial and inflammatory cells in reactive effusion fluids to create the basic map. This allows detection of a ‘second-foreign’ population which can be immunocharacterized further with the help of subtractive coordinate immunoreactivity pattern (SCIP) approach elaborated here.

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.

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.

SOX6 Expression Is Sensitive for Peritoneal Epithelioid Malignant Mesothelioma, But Not Specific in the Differential Diagnosis With Tubo-ovarian Serous Neoplasia.

Primary peritoneal malignant mesothelioma (MM) can demonstrate morphologic overlap with low-grade and high-grade tubo-ovarian serous neoplasms; it is also biologically and prognostically distinct from benign mesothelial proliferations. Currently, there is no single biomarker that can definitively distinguish these neoplasms. Sex-determining region Y box 6 (SOX6) immunohistochemistry has been recently described to differentiate pleural epithelioid MM from lung adenocarcinoma, but it has not been evaluated in the peritoneum. SOX6 immunohistochemistry was performed on 43 peritoneal epithelioid MM, 7 peritoneal biphasic MM, 5 well-differentiated papillary mesotheliomas, 5 serous borderline tumors, 29 low-grade serous carcinomas (LGSCs), 20 high-grade serous carcinomas (HGSCs), and 25 cases of peritoneal reactive mesothelial hyperplasia. Quantitative SOX6 expression in epithelioid MM (median, 100% of tumor cells) was significantly greater than in LGSC/serous borderline tumor (median, 90%; P=0.004) and HGSC (median, 45%; P=0.0001). However, when SOX6 is expression is defined as ≥10% of tumor cells, there was no significant difference in the rate of SOX6 positivity between epithelioid MM (41/43, 95%), LGSC (28/29, 97%; P=1.0), and HGSC (17/20, 85%; P=0.16). Quantitative extent of SOX6 expression in epithelioid MM was significantly greater than in biphasic MM (median, 0%; P=0.0001), well-differentiated papillary mesothelioma (median, 20%; P=0.001), and reactive mesothelial hyperplasia (median, 20%; P=0.0001), but not significantly different from flat quiescent mesothelium (median, 90%; P=0.82). SOX6 immunohistochemistry is 95% sensitive for peritoneal epithelioid MM, but is also consistently expressed in LGSC and HGSC, negating its usefulness in this common differential diagnosis. SOX6 also shows variable expression across the spectrum of reactive, benign neoplastic, and malignant mesothelial lesions of the peritoneum, and does not appear to be diagnostically useful in distinguishing benign from malignant mesothelial proliferations.

Malignant pleural mesothelioma showing rare morphology indistinguishable from myxofibrosarcoma concomitant with EGFR-mutated lung adenocarcinoma: A case report.

Introduction and importancePrimary tumors of the pleura are rare, with malignant mesothelioma being the most common of these neoplasms. Pathological diagnosis of sarcomatoid mesothelioma can be more challenging than that of epithelioid malignant mesothelioma because of its similarities with true sarcomas and restricted or inconsistent expression of mesothelial markers in immunohistochemistry analysis.Presentation of caseHere, we present an unusual case of malignant pleural mesothelioma concomitant with lung adenocarcinoma in a 72-year-old Japanese man, a smoker with no family history of cancer and asbestos exposure. Malignant pleural mesothelioma is composed of epithelial and spindle-shaped cells. Spindle-shaped cells with scant eosinophilic cytoplasm and hyperchromatic nuclei proliferated in abundant myxoid stroma containing thin-walled blood vessels, mimicking myxofibrosarcoma. The loss of BAP1 (BRCA1-associated protein 1) expression, as assessed by immunohistochemistry, and homozygous deletions of CDKN2A, detected using fluorescence in situ hybridization (FISH), were observed in both components. Targeted sequencing revealed that lung adenocarcinoma harbored EGFR mutations, whereas no mutations were detected in either component of biphasic mesothelioma.DiscussionAlthough alcian blue-stained mucins were detected in biphasic mesothelioma subsets, the clinicopathological significance of myxoid stroma in biphasic and sarcomatoid mesothelioma remains largely unknown.ConclusionOur case presented a unique morphology mimicking myxofibrosarcoma in a sarcomatoid component of biphasic mesothelioma; therefore, it raises a question on the clinicopathological significance of myxoid stroma in sarcomatous areas of biphasic and sarcomatoid mesothelioma.

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.

First-in-human phase 1 dose escalation study of HX009, a novel recombinant humanized anti-PD-1 and CD47 bispecific antibody, in patients with advanced malignancies.

2517 Background: HX009 is a novel humanized antibody fusion protein which binds to CD47 and PD-1 concurrently. HX009 significantly inhibited tumor growth in mouse xenograft models. In Cynomolgus monkeys, the highest non-severely toxic dose in repeat dose testing was 15mg/kg. HX009-I-01 (ClinicalTrials.gov：NCT04097769) is a first-in-human study evaluating the safety and efficacy of HX009 in subjects with advanced malignancies. Here we report the preliminary results from this study. Methods: The study is being conducted in Australia at 3 sites. The study design follows a 3+3 dose-escalation scheme, enrolling cohorts of at least 3 subjects (except the first dose level) sequentially until MTD or the maximum dose is reached. HX009 is administered as single agent every 2 weeks via intravenous infusion. The 7 dose levels planned are: 0.1mg/kg (1 subject), 0.3mg/kg, 1mg/kg, 2mg/kg, 3mg/kg, 5mg/kg, 7.5mg/kg. All AEs are graded using NCI CTCAE v5.0. Efficacy assessments are per RECIST 1.1. Blood samples are obtained for pharmacokinetics (PK) and for immunogenicity assessments by the development of Antidrug Antibodies. Results: As of the January 22 2021 cutoff date, 21 patients (12M/9F) with a median age of 69.0 years (range 38-86) have received dose levels of 0.1-7.5 mg/kg. Patients with the following tumor types have been enrolled: colorectal cancer (7), squamous cell carcinoma (3), endometrial cancer (2), breast cancer (3), malignant epithelioid mesothelioma (1), gallbladder cancer (1), pancreatic cancer (1), glioblastoma(1), ovarian cancer (1), gastroesophageal junction adenocarcinoma (1). Patients had received a median of 3 (range 1-9) prior anti-cancer regimens. Treatment-related AEs have been reported in 10 (47.6%) patients to date. Most AEs are grade 1 or 2. The most frequent treatment-related AEs include nausea (n = 2, G1), rash (n = 2, G1), vomiting (n = 2, G1), and decreased appetite (n = 2, G1). Only 1 treatment-related SAE of pneumonitis. One treatment-related anemia (G2), and no thrombocytopenia. No DLT was observed in all 7 dose levels. Among 18 patients who have had at least one post-baseline tumor assessments, partial responses (PR) have been achieved in 3 patients with the following tumor types (dose level): gallbladder adenocarcinoma (1mg/kg), triple negative breast cancer (5mg/kg), metastatic squamous cell carcinoma of head and neck (5mg/kg). In addition, there are 6 patients with best overall response of stable disease. As of the data cutoff date, 6 patients are still receiving treatment. Updated clinical and PK results will be presented at the meeting. Conclusions: HX009, on an every 2 weeks dosing schedule, up to 7.5 mg/kg, is well-tolerated, without any DLT to date. Antitumor activity was seen at 1 mg/kg and 5 mg/kg cohorts with objective responses in multiple tumor types; Further investigation in phase Ib/II studies is warranted. Clinical trial information: NCT04097769.

Histopathological typing in diffuse malignant epithelioid mesothelioma: implication for prognosis and molecular basis.

The prognostic impact of tumour grading, cytological and architectural patterns and stromal features in diffuse pleural malignant epithelioid mesothelioma (MEM) has been partly studied but not correlated to molecular features. We performed a retrospective study on 92 MEM in our department in order to assess the prognostic role of architectural and stromal patterns, especially tumour to stroma ratio. Secondly, based on The Cancer Genome Atlas (TCGA) database, we analysed the differentially expressed genes in prognostic groups of interest. Our results showed that tumour grading, tumour to stroma ratio and predominant pattern were related to overall survival, p≤0.001, p=0.01 and p=0.001, respectively. In univariate analysis, for high grade tumours hazard ratio (HR) was 4.75 (2.47-9.16), for stroma poor tumours HR=0.016, for predominant tubular or tubulopapillary pattern HR=0.044. In multivariate analysis, high grade tumours were related to overall survival [HR=3.09 (1.50-6.35), p=0.002] and predominant tubular or tubulopapillary pattern [HR=0.56 (0.32-0.99), p=0.045]. In TCGA analysis, after grading of diagnostic slides, we showed that KRTDAP and CXRCR1 expression was higher in low grade tumours, unlike PDZD7 and GPR176 expression which was higher in high grade tumours. FAM81B had a higher expression in stroma poor tumours. We did not find any differentially expressed genes in the architectural patterns group. Our work suggests that tumour grading is an important parameter in MEM with an underlying genomic basis. The role of tumour to stroma ratio needs to be investigated and might also have a genomic basis.