A Biphasic Pleural Tumor with Features of an Epithelioid and Small Cell Mesothelioma: Morphologic and Molecular Findings

Our plain-English summary of A Biphasic Pleural Tumor with Features of an Epithelioid and Small Cell Mesothelioma: Morphologic and Molecular Findings, by S. Hackman, R.D. Hammer, L. Layfield (Case Reports in Pathology, 2016).

The study

• Authors: S. Hackman, R.D. Hammer, L. Layfield
• Journal: Case Reports in Pathology
• Published: 2016;2016:1532424
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

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.

In plain English

This case report from pathologists at the University of Missouri described one 78-year-old man with a tumor of the pleura, the lining around the lung. The article states that the patient had no exposure to cigarette smoke or asbestos. The patient came to the emergency department with two weeks of shortness of breath, cough and fatigue. Imaging showed a large right-sided fluid collection and a 4.4 × 3.0 × 4.2 cm mass on the pleura. Under the microscope the tumor had two parts. One looked like epithelioid mesothelioma. The other, which made up most of the tumor, was made of small round cells that partly resembled a different rare cancer, desmoplastic small round cell tumor (DSRCT). Staining tests gave different marker patterns in the two parts. Genetic tests did not find the gene fusion that defines most DSRCTs. They did find many lost chromosome regions, some overlapping losses described in mesotheliomas. The authors concluded the tumor was a small cell mesothelioma. Chemotherapy was planned, and the article does not report the outcome.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Case report (single patient) with discussion of published findings on small cell mesothelioma and DSRCT
• Who was studied: One 78-year-old Caucasian man seen at an emergency department; the authors are from the Department of Pathology, University of Missouri, Columbia, USA. The date of presentation is not given.
• Exposure: No asbestos exposure: the article states the patient had no exposure to cigarette smoke or asbestos. No fiber type or job exposure is described.
• Main results:
  • Chest imaging showed a large right-sided pleural effusion, a 4.4 × 3.0 × 4.2 cm pleura-based lesion and a second 1.6 × 1.0 × 1.2 cm pleura-based lesion. 4.2 liters of fluid were drained.
  • The biopsy showed a biphasic tumor: papillary structures of large polygonal cells, plus a small round cell population that made up the majority of the tumor.
  • The larger cells stained positive for CK5/6, pan cytokeratin, calretinin, D2-40 and CD99. The small cell component stained for CD99, WT1, FLI1, CD15, cytokeratin, cytoplasmic Golgi MyoD1 and focally S100. Both populations were negative for desmin.
  • FISH testing was done on 100 tumor cells. In 94% of nuclei only a single intact copy of the EWSR1 signal was found. 0% of nuclei showed separation of the signals, so no EWSR1 rearrangement was seen.
  • Array CGH showed loss of heterozygosity of 6p and 6q. It also showed deletions and losses on chromosomes 1, 3, 5, 6, 9, 10, 11, 13, 17, 18, 20 and 22 and on the distal long arm of the Y chromosome, including loss of the WT1 and EWSR1 gene regions.
  • RT-PCR at an outside laboratory found no EWSR1-WT1, EWSR1-FLI1 or EWSR1-ERG fusion transcripts.
  • The tumor lost the 9p21 region and the 22q12 region containing the NF2 gene. The authors noted that several of the tumor's losses overlap losses described in malignant mesotheliomas.
  • PET/CT showed multiple right-sided pleura-based masses and no metastatic disease. The patient agreed to begin carboplatin/pemetrexed chemotherapy. No outcome is reported.
• The authors' conclusion: The authors concluded that the tumor was a small cell mesothelioma, with the small cell component focally resembling a DSRCT and elsewhere a blastemal-like mesothelioma. They wrote that the relationship between small cell mesothelioma and DSRCTs is unclear.
• Limitations the authors state:
  • The authors stated that the exact significance of the chromosome losses is unknown.
  • The authors stated that more microarray data from DSRCTs are needed to tell which, if any, of the patient's chromosomal changes recur in that tumor type.

Topics

Medical terms in this study, explained in our Lexicon: Biphasic Mesothelioma, Epithelioid, Mesothelioma, Sarcomatoid, Desmoplastic Mesothelioma, Desmoplastic Small Round Cell Tumor, Translocation, Pleura.

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