Mesotheliomas with small cell features: report of eight cases

Abstract

Mesotheliomas with small cell morphology are rare and only one study of such cases has been published. As a result of their rare occurrence, some investigators have cast doubt on the existence of such a histologic variant of mesothelioma. This investigator reports a series of eight cases of epithelioid mesothelioma with small cell features, all of which originated in the pleura. Seven of the patients were men and one was a woman. Four patients had a history of asbestos exposure. Histologically, four of the mesotheliomas were epithelioid and four biphasic. The proportion of small cells seen in these cases constituted 80 to 100% of the tumor included in the biopsy material and 15 to 20% of the tumor present in the pneumonectomy specimens. Immunoreactivity for calretinin, keratin 5/6, keratin 7, pan-keratin, WT1, podoplanin, and mesothelin was seen in all cases tested for these markers. All of the cases were negative for MOC-31, Ber-EP4, CEA, CD15, TAG-72, TTF-1, chromogranin A, synaptophysin, CD99, and desmin. The mean survival of the six patients for whom this information was available was 8.2 months. It is important for pathologists to be aware that mesotheliomas can present small cell features and, because of this, they can be confused with other malignancies that can exhibit similar morphology. The value of immunohistochemistry in the differential diagnosis of these tumors is discussed.

Systemic Therapy Use and Outcomes After Relapse from Preoperative Radiation and Extrapleural Pneumonectomy for Malignant Pleural Mesothelioma

“…However, two cases showed transformation to more aggressive histological subtypes with sarcomatoid and small cell histology on surgical biopsy of relapsed disease. The former is associated with an aggressive disease course, resistance to chemotherapy, and poor prognosis, and the latter is a rare variant with limited clinical data described in the literature . These findings are limited by small numbers but are relevant with respect to selection of subsequent systemic therapy given emerging treatments and clinical trials restricted to histological subtype such as antimesothelin agents in epithelioid mesothelioma, or ADI‐PEG 20 in patients with biphasic or sarcomatoid subtypes (NCT02709512), as well as the lower response rates to chemotherapy in nonepithelioid subtypes .…”

Application of immunohistochemistry in the diagnosis of epithelioid mesothelioma: a review and update

“…The percentage of calretinin expression reported has ranged from 6% to 23% in lung adenocarcinomas [2,9,11,17,19,20], 31% to 38% in serous carcinomas [18,21,22], 15% to 74% in breast carcinomas [23,24], and 0% to 10% in renal cell carcinomas [21,[25][26][27]. Other carcinomas that have been reported to be calretinin positive include squamous cell carcinomas of the lung (23%-40%) [2,6,26,28,29] and small cell lung carcinomas (41%-49%) [26,28], 2 tumors that, when they involve the pleura, can potentially be confused with mesothelioma [29,30]. Until relatively recently, anti-calretinin monoclonal antibodies such as the DAK-Calr 1, 5A5, and Z11-E3 have become commercially available, but only one study has been published comparing one of these antibodies (DAK-Calr 1) with one of the polyclonal antibodies that has frequently been used in published investigations [12].…”

Guidelines for Pathologic Diagnosis of Malignant Mesothelioma 2017 Update of the Consensus Statement From the International Mesothelioma Interest Group

“…50 Small cell mesotheliomas need to be distinguished from small cell carcinomas of the lung, desmoplastic small round cell tumors, lymphomas, and other tumors with small cell morphology. 51 Desmoplastic mesotheliomas may mimic fibrous pleuritis. Because each broad histologic category has its own distinctive differential diagnosis, the immunostains selected for further workup of a patient with MM are dictated by the tumor's histologic category.…”