Abstract
Malignant mesotheliomas are generally classified into epithelioid, sarcomatoid, desmoplastic, and biphasic types with rare reports of a small cell form. These small cell variants display some morphologic overlap with desmoplastic small round cell tumors (DSRCTs) which generally occur within the abdominal cavity of young males and are defined by a characteristic t(11;22)(p13;q12) translocation. However, there are rare reports of DSRCTs lacking this translocation. We present a 78-year-old man with a pleura-based biphasic neoplasm with features of both epithelioid mesothelioma and a small cell blastema-like neoplasm. The epithelioid portion showed IHC reactivity for pan cytokeratin, CK5/6, D2-40, and calretinin and the small cell portion marked with CD99, pan cytokeratin, WT1, FLI1, S100, CD200, MyoD1, and CD15. Fluorescence in situ hybridization testing for the t(11;22)(p13;q12) translocation disclosed loss of the EWSR1 gene in 94% of tumor cell nuclei, but there was no evidence of the classic translocation. Array based-comparative genomic hybridization (a-CGH) confirmed the tumor had numerous chromosome copy number losses, including 11p15.5-p11.12 and 22q12.1-q13.33, with loss of the EWSR1 and WT1 gene regions. Herein, we report novel complex CGH findings in a biphasic tumor and review the molecular genetic alterations in both mesothelioma and DSRCTs.
Highlights
Primary tumors of the pleura are relatively uncommon and are divided by the World Health Organization (WHO) 2014 classification into mesothelial tumors, lymphoproliferative disorders, and mesenchymal tumors [1, 2]
Primary neoplasms with a small cell morphology arising within the pleura are rare and include desmoplastic small round cell tumors (DSRCTs) [2, 3] and pleuropulmonary blastomas [4]
Fluorescence in situ hybridization (FISH) testing was performed on 100 interphase cells from the pleura-based tumor using dual color break-apart probes for 5EWSR1 and 3EWSR1 gene regions at 22q12. 94% of nuclei had only a single intact copy of the EWSR1 fusion signal, but 0% of nuclei had separation of the 5 and 3 signals
Summary
Primary tumors of the pleura are relatively uncommon and are divided by the World Health Organization (WHO) 2014 classification into mesothelial tumors, lymphoproliferative disorders, and mesenchymal tumors [1, 2]. We describe a patient’s tumor with histopathological and immunohistochemical features of a mixture of a small cell malignancy and an epithelioid mesothelioma that had multiple complex chromosomal abnormalities on microarray, including the loss of 11p15.5-p11.12 and 22q12.1q13.33 regions. Immunohistochemical staining demonstrated the larger cells to be CK5/6, pan cytokeratin, calretinin, D2-40, and CD99 positive (Figures 5(a) and 5(b)), while the small cell component was immunoreactive for CD99, WT1, FLI1, CD15, cytokeratin, cytoplasmic Golgi MyoD1, and focally S100 (Figures 6(a) and 6(b)).
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