Mesothelial Origin Research Articles

Flow cytometry of non-hematopoietic cells in canine effusions.

The identification of non-hematopoietic cells in effusions is a diagnostic challenge in cytology. Biopsies from mesothelium or primary lesions are infrequently performed in clinical settings and immunochemistry on smears or immunohistochemistry on cell blocks are the most common ancillary test to refine the cytological diagnosis. Cavitary effusions are an ideal matrix for flow cytometry and the availability of a cytometric panel to describe non-hematopoietic cells would represent a useful tool. Here we present the results of the flow cytometric and immunohistochemical determination of cytokeratin (CK), vimentin (VIM) and desmin (DES) in 36 canine effusions. The concordance between the two methods was perfect for CK (100%), substantial for VIM (77.8%), and almost perfect for DES (97.2%). The panel was interpreted to define the epithelial (CK+VIM-DES-), mesothelial (CK+VIM+DES+), or mesenchymal (CK-VIM+DES-) origin of the cells. Unexpected profiles were considered doubtful and observed patterns were individually discussed. The concordance of the panel interpretation between two methods was 75%. The evaluation of discordant and doubtful cases suggests a lower sensitivity of flow cytometry in detecting VIM expression and revealed a high frequency of VIM+ epithelial cells, variable expression of VIM in mesothelial cells, and an important role of DES in excluding an epithelial origin when positive. Multicentric studies based on histopathological diagnoses are necessary to confirm these findings and evaluate the diagnostic utility of the panel to refine cytological diagnosis. Our results show that flow cytometry can be a timesaving alternative to IHC on cell blocks in clinical settings to detect CK, VIM and DES expression. The interpretation of the panel is similar in most cases; however, occasional discordant results, particularly for VIM, may occur.

A seed or soil problem in early endometriosis: stromal cell origin drives cellular invasion and coupling over mesothelial cell origin

To study the role of the mesothelial cells in early endometriosis lesion formation by assessing in vitro cell to cell communication and invasion of endometrial cells across a mesothelial cell monolayer, with both cell types derived from both endometriosis and control patients. Laboratory based experimental study SETTING: University hospital and laboratory PATIENT(S): Consenting reproductive aged women who underwent laparoscopy for gynecologic reasons and were confirmed to either have endometriosis with pathology tissue diagnosis (n=8) or no endometriosis (n=8) at the time of surgery INTERVENTION: Primary stromal cells cultured from endometrial pipelle biopsies and primary mesothelial cells cultured from peritoneal explants were utilized in trans-mesothelial invasion assays and gap junction coupling assays. Comparison of potential for lesion formation, using in vitro models, of both primary endometrial and mesothelial cells from endometriosis and control patients, establishing the former as the primary disease driver. When comparing mesothelial cells from control patients to mesothelial cells from endometriosis patients, there was no significant difference in the amount of stromal cell invasion across either barrier. In contrast, when comparing stromal cell origin, the amount of invasion by endometriosis stromal cells was greater than control stromal cells regardless of whether the mesothelial cell monolayer was derived from disease or control patients. Additionally, primary mesothelial cells induced more gap junction coupling, a requirement for invasion, in stromal cells from endometriosis than control patients, again independent of mesothelial origin. The notable exception was mesothelial cells derived from endometriotic lesion affected areas that showed depressed ability to support invasion. While both endometrial and mesothelial cells need to function for establishment of endometriosis lesions, the endometrium seems to be the key player, serving as an ideal target for diagnostic strategies and therapeutic intervention. This notion is consistent with prior studies, however we are the first to directly test both primary mesothelial and endometrial cells from endometriosis and control patients to compare propensities for mesothelial invasion.

Investigation of HEG1, VISTA (VSIR) and PD-L1 expression levels in malignant mesothelioma by immunohistochemical methods and their relationship with histological subtypes

Malignant Mesothelioma is a primary malignant tumor of the mesothelium lining the pleura, pericardium, peritoneum and tunica vaginalis of the testis with a poor prognosis. The epithelioid subtype is graded as high and low grade in the 2021 WHO classification of thoracic tumors. Recently, promising results from clinical trials of treatment with immune checkpoint inhibitors are reported. The aim of our study was to shed light on clinical studies on potential immune checkpoint inhibitors by examining VISTA and PD-L1 expression levels as well as HEG1 in malignant mesothelioma subtypes. Our study included 69 cases diagnosed with ‘malignant mesothelioma, well-differentiated papillary mesothelial tumor, atypical mesothelial hyperplasia’ at Dicle University Faculty of Medicine Department of Pathology between 2015 and 2021. Primary antibodies against HEG1, VISTA, and PD-L1 were used in the immunohistochemical study. The results showed a significant relationship between PD-L1 expression and sarcomatoid and high-grade epithelioid malignant mesotheliomas. VISTA was detected at a high rate in epithelioid malignant mesotheliomas and was negative in non-mesothelial tumors. HEG1 was positively monitored in mesothelial-derived tumors and negatively monitored in non-mesothelial tumors. The obtained results suggest that HEG1 could be further explored as a useful marker in determining mesothelial origin and that the expression levels of VISTA and PD-L1 markers may vary in histological subtypes in the selection of drugs for the treatment of malignant mesothelioma.

Exploring the histogenesis of STK11 adnexal tumour using electron microscopy

STK11 adnexal tumour is a recently described female genital tract tumour, usually identified in a paratubal location, often associated with Peutz-Jeghers syndrome (PJS) and with STK11 gene alterations identified in most of the cases. Morphologically, this tumour is composed of cells arranged in a variety of patterns, including cords, trabeculae, tubules and cystic and acinar structures. The cells are only moderately pleomorphic and mitotic activity is variable. As tumour cells express epithelial, sex cord stromal and mesothelial markers, STK11 adnexal tumour may be of sex cord stromal, epithelial or mesothelial origin; a Wolffian origin has also been suggested. We report the ultrastructural features of two STK11 adnexal tumours and compare their ultrastructural features with those of other sex cord stromal tumours, a granulosa cell tumour cell line, as well as the known ultrastructural features of epithelial, mesothelial and Wolffian cells. On ultrastructural examination, two STK11 adnexal tumours showed an admixture of elongated cells with regular elongated nuclei and polygonal cells with nuclei showing markedly irregular outlines and prominent nucleoli. Extracellular collagen fibres were identified. These are common ultrastructural features of sex cord stromal tumours, principally sex cord tumour with annular tubules; no ultrastructural features of epithelial, mesothelial or Wolffian cells were found. These findings in conjunction with the shared clinical and genetic association with PJS and shared molecular changes in STK11 gene suggest that STK11 adnexal tumour represents a poorly differentiated sex cord tumour.

Adenomatoid tumor uterus coexisting with high grade serous carcinoma ovary: An incidental finding with literature review

ABSTRACT Adenomatoid tumor is a benign neoplasm of mesothelial origin encountered most often in the male and female genital tracts. These are generally small, benign lesions and are mostly incidental findings. Here we present a case of adenomatoid tumor uterus incidentally detected in a 39-year-old female who was operated for cystic lesion in the ovary.

A giant mediastinal coelomic cyst resected by uni-portal VATS

médiastinal Coelomic cysts are rare cysts of mesothelial origin. They represent 4 to 11% of all mediastinal tumors. It affects both men and women. The diagnosis is often made in adulthood. They are often asymptomatic We repport the rare case of mesothelial cyst of mediastinum. A 38-year-old woman with no medical history, she was reffered to our department after chest X-ray showed a giant anterior madiastinum. The lesion was resected by VATS, which revealed a médiastinal cystic that extends from the top of the anterior mediastinum to the diaphragm. On histological section, the cystic wall is seat of a significant inflammatory, lined by a flattened epithelial lining of mesothelial type, conclusive to mediastinal pleural mesothelial cyst. The prognosis is excellent in the short and long term.

Malignant Para-Testicular Mesothelioma: A Rare Presentation in the Tunica Vaginalis of an Elderly Male With No Prior Asbestos Exposure.

Malignant mesothelioma of the tunica vaginalis is an extremely rare and aggressive tumor that is frequently encountered in elderly patients. The diagnosis of malignant mesothelioma of the tunica vaginalis poses a diagnostic challenge due to its infrequency and nonspecific clinical presentation. Histopathological examination and immunohistochemical staining are essential in differentiating this tumor from other para-testicular masses and establishing a definitive diagnosis. Early detection and comprehensive treatment planning are crucial for improving the prognosis and overall outcomes for patients with this rare malignancy. We present a report of malignant mesothelioma of the tunica vaginalis in a 78-year-old male patient with no history of asbestos exposure who presented with a large infiltrative left para-testicular mass. Histopathological examination revealed a biphasic proliferation composed of epithelioid and spindle cells with infiltrative features, foci of necrosis, and increased mitotic figures. Immunohistochemical staining exhibited positive staining for WT1, D2-40, and calretinin, supporting the mesothelial origin of the tumor. Notably, BerEP4 staining was negative, arguing against carcinoma. Immunostaining for keratin 5 was positive, supporting the mesothelial differentiation. The Ki67 proliferation index was high. The differential diagnosis included adenomatoid tumors, germ cell tumors, and pleomorphic sarcoma. We aim to discuss the clinical presentation, diagnostic approach, and therapeutic approaches of this rare entity.

MR Imaging Findings of Uterine Adenomatoid Tumors.

Adenomatoid tumor is a rare benign genital tract neoplasm of mesothelial origin. Uterine adenomatoid tumors occur in the outer myometrium and may mimic leiomyomas. Because hormonal treatment is not applicable to adenomatoid tumors and laparoscopic enucleation is not easy as myomectomy, it is important to differentiate adenomatoid tumors from leiomyomas for the adequate treatment. The purpose of this study is to evaluate the MRI findings of adenomatoid tumor for the differentiation from leiomyoma. MRI findings of surgically proven 10 uterine adenomatoid tumors in 9 women were retrospectively evaluated with correlation to histopathological findings. All 10 tumors appeared as solid myometrial masses and showed heterogeneous signal intensity with admixture of partially ill-defined slight high-intensity areas containing abundant tubular tumor cells and well-defined myoma-like low-intensity areas reflecting smooth muscle hypertrophy on T2WI including 4 lesions with peripheral ring-like high intensity. High-intensity areas on T2WI tended to show high intensity on diffusion-weighted imaging (DWI) with relatively high apparent diffusion coefficient (ADC), suggesting T2 shine-through effect due to abundant tubules. Intra-tumoral hemorrhage revealed on MRI was rare. Early intense contrast-enhanced areas on dynamic contrast-enhanced study were observed dominantly within the high-intensity areas but rarely within the low-intensity areas on T2WI. The outer myometrial mass with the admixture of well-defined low- and ill-defined high-intensity areas on T2WI may be suggestive of adenomatoid tumor. Peripheral ring-like high intensity on T2WI and DWI may also be suggestive. Dynamic contrast-enhanced MR study may be helpful for the differentiation from leiomyoma.

Non-organ mesothelial cyst of the abdominal cavity. Clinical observation

Non-organ cysts of mesothelial origin are one of the groups of cystic neoplasms with rare and difficult-to-diagnose pathology of the abdominal cavity and retroperitoneal space. Today, the etiological factors remain the subject of interdisciplinary discussions, their clinical manifestations are non-specific, and their differential diagnosis is diverse. Often, these neoplasms become accidentally detected during surgical interventions or during routine diagnostic examinations. Currently, there are no uniform standards or recommendations to treat such diseases, however, according to literature sources, there is a consensus that mesothelial cysts of the retroperitoneal space and abdominal cavity should be completely removed within healthy tissues. Today, modern medical achievements and accumulated long-term experience allow us to successfully diagnose and perform radical treatment for any localization of such neoplasms. We present our own experience from the clinical practice of successful surgical treatment of non-organ cysts of mesothelial origin.

Adenomatoid tumor with extensive reactive smooth muscle: a diagnostic dilemma

Abstract Introduction/Objective Adenomatoid tumors are slow-growing benign tumors of mesothelial origin. They comprise 30% of all tumors of the paratesticular area. In this location, they commonly involve the epididymis, spermatic cord, ejaculatory duct and rarely testicular parenchyma. Histologically, a spectrum of growth patterns can be seen, such as adenoid, tubular, glandular, solid, or cystic. In some cases, a smooth muscle component can also be present. The purpose of this report is to describe a case of adenomatoid tumor with exuberant smooth muscle component, mimicking leiomyoma. Methods/Case Report A 28-year-old male presented with painless left inguinal bulge. He noticed it five years prior, and it had been slowly growing since then. Examination revealed a paratesticular mass which was subsequently excised. Grossly, the tumor was firm with smooth, white-tan cut surfaces. Microscopically, the tumor was well- circumscribed, showing predominance of smooth muscle bundles and rare cuboidal to ovoid cells in tubular growth pattern. In the background there was little intervening stroma. Immunohistochemical stains showed the cuboidal cells to be positive for WT1 and calretinin, confirming the mesothelial origin. Diagnosis of adenomatoid tumor was rendered. In contrast to adenomatoid tumors, leiomyomas are whiter and firmer on gross examination and lack the characteristic tubules or cystic spaces lined by mesothelial cells. Results (if a Case Study enter NA) N/A Conclusion Exuberant smooth muscle differentiation in adenomatoid tumor can mislead to diagnosis of leiomyoma. Careful inspection for tubules of mesothelial origin and appropriate immunohistochemical stains are key to accurate diagnosis. Pathologists need to be aware of this potential pitfall.

Dermoid Cyst of the Mesentery of the Jejunum Following Appendectomy: A Clinical Case

Mesenteric cysts and cystic mesenteric tumors are very rare abdominal growths. They may be localized all over the mesentery, from the duodenum to the rectum, however, they are mostly found in the ileum and right colon mesentery. There are several classifications of these formations, among which the one based on histopathologic features including 6 groups has been most commonly used: 1) cysts of lymphatic origin--lymphatic (hilar cysts) and lymphangiomas; 2) cysts of mesothelial origin--benign or malignant mesothelial cysts; 3) enteric cysts; 4) cysts of urogenital origin; 5) dermoid cysts; and 6) pseudocysts-infectious or traumatic etiology. A dermoid cyst is a benign, epithelial-lined cavitary lesion composed of ectoderm and mesoderm that can arise anywhere in the body, with a tendency to develop in midline structures. In 20% - 45% of cases, accompanying diseases that were not previously clinically manifested can be diagnosed during emergency interventions, requiring additional surgical interventions for their correction. The aim of the study is to demonstrate the successful treatment experience of a dermoid cyst of the mesentery of the jejunum, detected after traditional appendectomy. Clinical case: A mother brought her 9-year-old son, V., to the emergency department of the Kursk Regional Children’s Clinical Hospital with complaints of moderate-intensity pain in the right iliac region, multiple episodes of vomiting, and fever. Ultrasound features indicative of destructive appendicitis and peritonitis. In an emergency situation, after preoperative preparation, a traditional appendectomy was performed under intravenous anesthesia, using the Volkovich-Dyakonov approach. The postoperative period was uneventful. Moderate infiltration was observed on the control abdominal ultrasound examination, in the intestine (presumably the small intestine) in the right half of the abdominal cavity, with a solid formation measuring 27*33 mm, producing a dense acoustic shadow. On the 7th day after the initial intervention, a revision of the abdominal organs was performed. The loop of the jejunum with the formation was brought out into the wound. The capsule above the formation was dissected: the formation of bone density, when the capsule is separated, resembles a fecal stone in structure, considering the localization - a dermoid cyst. Step-by-step enucleation of the cyst was performed. The postoperative wound was tightly sutured in layers.

Chemosensitivity of three patient-derived primary cultures of canine pericardial mesothelioma by single-agent and combination treatment.

Canine mesothelioma is a rare malignant tumor that mostly affects body cavities, such as the pericardial and pleural cavities. Chemotherapy plays a crucial role in the treatment of canine mesotheliomas. We aimed to compare the antitumor effects of single-agent and combination chemotherapeutic agents on patient-derived primary cultures of canine pericardial mesothelioma established in this study. We planned to generate xenograft models for future studies. Effusion samples were collected from three dogs with histologically diagnosed pericardial mesothelioma and used for primary culture. Cultured cells were characterized by immunostaining for pan-cytokeratin AE1/AE3, vimentin, Wilms' tumor suppressor gene 1 (WT1), and cytokeratin 5 (CK5). To assess the tumorigenic properties of cells in the effusion and generate a xenograft model, the cell suspension was injected into a severe combined immunodeficient (SCID) mouse either subcutaneously (SC) or intraperitoneally (IP). Lastly, chemosensitivity of established primary cultures against four drugs, doxorubicin, vinorelbine, carboplatin, and gemcitabine, by single-agent treatment as well as combination treatment of carboplatin at a fixed concentration, either 10 or 100 μM, and gemcitabine at different concentrations ranging from 0-1000 μM was assessed by cell viability assay. Primary cultures were successfully generated and characterized by dual positivity for AE1/AE3 and vimentin and positive staining for WT-1 and CK5, confirming the mesothelial origin of the cells. In the xenograft models, SC mouse developed a subcutaneous mass, whereas IP mouse developed multiple intraperitoneal nodules. The masses were histopathologically consistent with mesotheliomas. The chemosensitivity assay revealed that carboplatin had the highest anti-tumor effects among the four tested single-agent treatments. Furthermore, carboplatin at 100 μM combined with gemcitabine at clinically relevant doses demonstrated the augmented anti-tumor effects compared to single-agent treatment. Primary cultures and xenograft models generated in this study could be useful tools for in vitro and in vivo studies of canine mesothelioma. Carboplatin is a highly effective chemotherapeutic agent against canine mesothelioma when used as a sole agent and in combination with gemcitabine.

Adenomatoid tumor of fallopian tube with intratumoral endometriosis: what mind doesn’t know, eyes don’t see

Adenomatoid tumor, a benign tumor of mesothelial origin, is seen most commonly in paratesticular tissue in males and uterus in females. Its incidence is extremely rare in the fallopian tube, with only few such case reports. In the present case, an incidental association of adenomatoid tumor of the fallopian tube with turbo-ovarian endometriosis and ipsilateral nonfunctioning kidney was seen. Intraoperatively, a small nodular lesion was seen over the tubal wall. On a detailed review of literature, we found very few cases of adenomatoid tumor of the fallopian tube. The other unique finding was the occurrence of intratumoral endometriosis within the adenomatoid tumor.

Mesenteric Cyst of Mesothelial Origin in Young Women: Literature Review and Case Report

Introduction: The mesenteric cyst is a rare type of abdominal tumor in the adult and pediatric population1, the mesothelial cysts are more frequent in young women 2,3, there are mainly 3 forms of clinical presentation4. The asymptomatic clinical presentation is the most frequent and is diagnosed incidentally in complementary tests or surgeries5. Clinical case: A 38-year-old woman diagnosed with a mesocolon-dependent mesenteric cyst of mesothelial origin at the splenic angle level, the triphasic abdominopelvic CT scan reported an 11x11 cm cyst with a volume of 403 cc, the biopsy reported a simple mesothelial cyst. Complete removal of the tumor was performed using a laparoscopic approach. Conclusion: The treatment of choice for tumors of the mesentery is the complete removal of the tumor, the mere aspiration of its contents or partial resection is doomed to recurrence 6.

The Mesenteric cyst of mesothelial origin in young women: Literature review and case report

The Mesenteric cyst of mesothelial origin in young women: Literature review and case report

ADENOMATOID TUMOR IN THE FALLOPIAN TUBE - A RARE CASE-INCIDENTAL FINDING

Adenomatoid tumours are less common benign neoplasm of mesothelial origin, which originates from the lining of organs. This tumour generally presents in both male and female genital tracts. [1-9]. In males, the tumour is usually foundin testis and epididymis while in females, the uterus and rarely fallopian tubes are the sites involved.Mostlty,thistumour is found incidentally.Grossly, adenomatoid tumors are usually smallin size (less than 2 cm) well-circumscribed, solitary masses that are tan, yellow, and solid [10].The histopathological examination revealed features of adenomatoid tumor supported by immunohistochemical stains positive for calretinin and cytokeratin and negative for CD34. These tumourshave a good prognosis upon surgical removal with no evidence of recurrence.We present a case where this rare tumour was found incidentally in the Salpingectomy specimen of a 39-year-old woman who underwent this procedure for permanent contraception as she requested the removal of tubes instead of blockage.

GIPR expression is induced by thiazolidinediones in a PPARγ-independent manner and repressed by obesogenic stimuli

Adipose tissue (AT) dysfunctions are associated with the onset of insulin resistance (IR) and type 2 diabetes mellitus (T2DM). Targeting glucose-dependent insulinotropic peptide receptor (GIPR) is a valid option to increase the efficacy of glucagon-like peptide 1 (GLP-1) receptor agonists in T2DM treatment. Nevertheless, the therapeutic potential of targeting the GIP/GIPR axis and its effect on the AT are controversial. In this work, we explored the expression and regulation of GIPR in precursor cells and mature adipocytes, investigating if and how obesogenic stimuli and thiazolidinediones perturb GIPR expression. Using publicly available gene expression datasets, we assessed that, among white adipose tissue (WAT) cells, adipocytes express lower levels of GIPR compared to cells of mesothelial origin, pericytes, dendritic and NK/T cells. However, we report that GIPR levels markedly increase during the in vitro differentiation of both murine and human adipocytes, from 3T3-L1 and human mesenchymal precursor cells (MSCs), respectively. Notably, we demonstrated that thiazolidinediones – ie. synthetic PPARγ agonists widely used as anti-diabetic drugs and contained in the adipogenic mix – markedly induce GIPR expression. Moreover, using multiple in vitro systems, we assessed that thiazolidinediones induce GIPR in a PPARγ-independent manner. Our results support the hypothesis that PPARγ synthetic agonists may be used to increase GIPR levels in AT, potentially affecting in turn the targeting of GIP system in patients with metabolic dysfunctions. Furthermore, we demonstrate in vitro and in vivo that proinflammatory stimuli, and especially the TNFα, represses GIPR both in human and murine adipocytes, even though discordant results were obtained between human and murine cellular systems for other cytokines. Finally, we demonstrated that GIPR is negatively affected also by the excessive lipid engulfment. Overall, we report that obesogenic stimuli - ie. pro-inflammatory cytokines and the increased lipid accumulation – and PPARγ synthetic ligands oppositely modulate GIPR expression, possibly influencing the effectiveness of GIP agonists.

Epididymal adenomatoid tumor: a case report and literature review

BackgroundAdenomatoid tumor is a very rare benign neoplasm of mesothelial origin affecting mainly female and male genital tracts. The diagnosis is challenging as this tumor mimics many differential diagnoses. The current literature offers only some case reports and short series of adenomatoid tumors.Case presentationA 47-year-old patient with unremarkable medical history presented for chronic mild pain of the right testis evolving for months. The physical examination shows a palpable right intrascrotal nodule of 10 mm in greatest diameter. The nodule was painful, mobile with firm consistency. The laboratory investigations were within normal limits, the scrotal ultrasonography showed a well-circumscribed predominantly hyperechoic intrascrotal nodule in the right epididymal head with heterogeneous echostructure. Excisional biopsy of the lesion was performed and the histopathological analysis showed a well-circumscribed tumor with microcystic and trabecular architecture made of small interconnected tubules and cysts lined by flattened cells with prominent vacuolization and thread-like bridging strands, consistent with an epididymal adenomatoid tumor. The postoperative course was uneventful and the patient was discharged. Four months after surgical treatment, the patient has no sign of the disease.ConclusionTesticular adenomatoid tumors are uncommon benign neoplasms with diagnostic challenge. Adenomatoid tumors arising in epididymis are managed by excisional biopsy with testis-sparing surgery avoiding unnecessary orchidectomy.

Uterine Serosal Inclusion Cysts with Greater Omentum Involvement in a Cat

A 7-year-old nulliparous Chinchilla queen was admitted to a veterinary clinic for routine ovariohysterectomy. Examination of the uterus, greater omentum and varicose ovarian veins revealed multiple thin-walled cysts filled with a transparent fluid over the serosal surfaces of these organs. Histologically, the cysts were of variable size, filled with a small amount of mucinous fluid, and had thin walls that contained hypocellular collagen and a few small calibre vessels. The inner and outer epithelium of the cyst walls and the cells that lined the uterine serosa were immunopositive for cytokeratin and vimentin, suggesting a mesothelial origin. Alpha-smooth muscle actin immunolabelling was patchy or continuous in smooth muscle in the wall of many of the cysts.

A diagnostic approach to paratesticular lesions with tubulopapillary architecture: a series of 16 serous borderline tumors/low-grade serous carcinoma and 14 well-differentiated papillary mesothelial tumors and mesothelioma

As there is limited literature on paratesticular tumors of müllerian and mesothelial origin, we reviewed archived cases of serous borderline tumors (n=15), low-grade serous carcinoma (n=1), well-differentiated papillary mesothelial tumors (WDPMTs; n=2), and mesothelioma (n=12), for relevant clinicopathologic features. Molecular profiling data from the American Association for Cancer Research (AACR) GENIE registry was accessed for 8 additional patients with testicular mesothelioma. For tumors of mesothelial origin, the median age at surgical excision was 62 years, the median size was 4.5cm, and they consistently exhibited positivity for mesothelial markers (CK5/6, calretinin, WT1, and D2-40). Recurrent alterations of the NF2 gene were identified in 3 of 8patients (38%), and alterations of BAP1 and CDKN2A were relatively infrequent. While one patient with WDPMT had a recurrence, a second patient with WDPMT progressed to a biphasic mesothelioma 2 years after initial resection. For tumors of müllerian origin, the median age at surgical excision was 45 years, the median size was 2.5cm, and these exhibited consistent positivity for ER, WT1, and PAX8. Although no recurrences were documented in patients with serous borderline tumors, a single patient with a low-grade serous carcinoma developed widely metastatic disease and died of disease-related complications. Our study emphasizes the need for close clinical follow-up in patients with WDPMT and highlights the prognostic significance of documenting invasive behavior in tumors of müllerian origin as they can have an aggressive clinical course. Finally, our results suggest that NF2 alterations may play an important role in the pathogenesis of testicular mesothelioma.