Microcystic variant malignant mesothelioma presenting as a localized paraspinal mass

NR4A3 fusions characterize a distinctive peritoneal mesothelial neoplasm of uncertain biological potential with pure adenomatoid/microcystic morphology

A focal adenomatoid-microcystic pattern is not uncommon in peritoneal mesothelioma, but tumors composed almost exclusively of this pattern are distinctly rare and have not been well characterized. A small subset of mesotheliomas (mostly in children and young adults) are characterized by gene fusions including EWSR1/FUS::ATF1, EWSR1::YY1, and NTRK and ALK rearrangements, and often have epithelioid morphology. Herein, we describe five peritoneal mesothelial neoplasms (identified via molecular screening of seven histologically similar tumors) that are pure adenomatoid/microcystic in morphology and unified by the presence of an NR4A3 fusion. Patients were three males and two females aged 31-70 years (median, 40 years). Three presented with multifocal/diffuse and two with a localized disease. The size of the individual lesions ranged from 1.5 to 8 cm (median, 4.7). The unifocal lesions originated in the small bowel mesentery and the mesosigmoid. Treatment included surgery, either alone (three) or combined with hyperthermic intraperitoneal chemotherapy (two), and neoadjuvant or adjuvant chemotherapy (one case each). At the last follow-up (6-13 months), all five patients were alive and disease-free. All tumors were morphologically similar, characterized by extensive sieve-like microcystic growth with bland-looking flattened cells lining variably sized microcystic spaces and lacked a conventional epithelioid or sarcomatoid component. Immunohistochemistry confirmed mesothelial differentiation, but most cases showed limited expression of D2-40 and calretinin. Targeted RNA sequencing revealed an NR4A3 fusion (fusion partners were EWSR1 in three cases and CITED2 and NIPBL in one case each). The nosology and behavior of this morphomolecularly defined novel peritoneal mesothelial neoplasm of uncertain biological potential and its distinction from adenomatoid variants of conventional mesothelioma merit further delineation as more cases become recognized.

Cytological Assessment of Desmoplastic Malignant Pleural Mesothelioma in an Autopsy Case

INTRODUCTION

Desmoplastic malignant pleural mesothelioma (DMPM) is a sarcoma-type mesothelioma, comprising approximately 5% of malignant pleural mesotheliomas. Although effusion cytology is commonly used as the primary diagnostic approach for mesothelioma, it may not be useful for DMPM because of the presence of desmoplasia and bland cellular atypia. We report a case, and previously undescribed cytological features, of DMPM that was diagnosed during autopsy.

CASE PRESENTATION

A man in his 60s with a history of occupational asbestos exposure was referred to our hospital with right chest pain. A chest CT scan showed right pleural effusion. Thirteen months later, the patient died of respiratory failure. During autopsy, scrape-imprint smears were prepared and cytology of pleural effusions was performed. The scrape-imprint smear samples showed spindle cells with mild nuclear atypia and grooves with fibrous stroma. Pleural effusion cytology revealed spindle cells with mild nuclear atypia, as well as grooves with loose epithelial connections. Histological examination of the right pleura showed spindle cells proliferating with dense collagen fibers, as seen in the cytological samples, thus indicating a diagnosis of DMPM, which was confirmed by fluorescence in situ hybridization.

CONCLUSION

Cytological procedures such as pleural effusion cytology and scrape-imprinting cytology may help in diagnosing rare tumors such as DMPM.

Peritoneal adenomatoid (microcystic) mesothelioma

There are several reports of pleural adenomatoid (microcystic) mesothelioma, but peritoneal adenomatoid mesothelioma is extremely rare. A 64-year-old Japanese woman presented with no symptoms and no asbestos exposure history. An abdominal computed tomography scan revealed multiple hypervascular masses on the liver surface, pelvic cavity and anterior peritoneum. Over 10 pieces of the multiple resected tumors showed numerous microcysts composed of a bland mesothelial cell background with rich capillary vessels. Focally, atypical cells with bizarre nuclei with prominent nucleoli were observed. Adenomatoid mesothelioma was suspected based on histochemical, immunohistochemical and fluorescence in situ hybridization findings. The tumors relapsed 4 years later and metastasized to the lung, but the patient remains alive 7 years after the first tumor resection surgery. Although the prognosis of adenomatoid mesothelioma of pleural origin is poor, the progression of this peritoneal case is slow.

Localized malignant mesothelioma, an unusual and poorly characterized neoplasm of serosal origin: best current evidence from the literature and the International Mesothelioma Panel

Localized malignant mesotheliomas (LMM) is an uncommon and poorly recognized neoplasm. Its pathologic diagnosis is often surprising in patients with serosal/subserosal based localized tumors that are clinically suspicious for metastatic lesions or primary sarcomas. Once a tumor is diagnosed as "mesothelioma", LMM is often mistaken for diffuse malignant mesothelioma (DMM). Best currently available evidence about LMM was collected from the literature and cases diagnosed by members of the International Mesothelioma Panel (IMP). One hundred and one (101) LMM have been reported in the English literature. Patients had localized tumors with identical histopathologic features to DMM. Patients ranged in age from 6 to 82 years; 75% were men. Most (82%) of the tumors were intrathoracic. Others presented as intrahepatic, mesenteric, gastric, pancreatic, umbilical, splenic, and abdominal wall lesions. Tumors varied in size from 0.6 to 15 cm. Most patients underwent surgical resection and/or chemotherapy or radiation therapy. Median survival in a subset of patients was 29 months. Seventy two additional LMM from IMP institutions ranged in age from 28 to 95 years; 58.3% were men. Sixty tumors (83.3%) were intrathoracic, others presented in intraabdominal sites. Tumors varied in size from 1.2 to 19 cm. Median survival for 51 cases was 134 months. Best evidence was used to formulate guidelines for the diagnosis of LMM. It is important to distinguish LMM from DMM as their treatment and prognosis is different. A multidisciplinary approach is needed for the diagnosis of LMM as it shows identical histopathology and immunophenotype to DMM.

Fine needle aspiration biopsy of metastatic malignant mesothelioma with myxoid change and signet ring cells: A case report and review of the literature

Malignant mesothelioma (MM) is a rare neoplasm, which is most commonly encountered in cytology through effusion specimens. Fine needle aspiration biopsy of MM, particularly the epithelioid subtype, can be a source of diagnostic difficulty and may mimic sampling of an adenocarcinoma. This is the first case report to demonstrate abundant extracellular myxoid material and numerous intracellular vacuoles, including signet ring cells, in a fine needle aspirate of metastatic MM. A review of the literature for myxoid change and vacuoles in fine needle aspiration biopsies of MM discloses that vacuoles are found in up to 35% of aspirates of MM, but myxoid change is very rare, reported in <5% of the cases. Cytologists should be aware of this rare morphologic pattern of metastatic epithelioid MM.