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
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 [
Cytogenetic and molecular studies are often required to accurately distinguish DSRCT from other small blue cell neoplasms. Approximately, 96% of DSRCTs have a characteristic chromosomal translocation t(11;22)(p13;q12) that produces a fusion of
Here 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 22q12.1-q13.33 regions. These deletions, involving the
A 78-year-old Caucasian man presented to the emergency department with a two-week history of shortness of breath, nonproductive cough, decreased exercise tolerance, and fatigue. His past medical and surgical history was significant for gastrointestinal reflux disease and resection of a stage I melanoma from his scalp. He had no exposure to cigarette smoke or asbestos. Physical examination revealed decreased breath sounds and dullness to percussion over his right hemithorax. Laboratory values were within normal limits except for an elevated creatinine. Chest X-rays disclosed a large right-sided pleural effusion with right middle and lower lobe collapse. There was a 4.4 × 3.0 × 4.2 centimeter (cm) pleura-based, enhancing lesion adjacent to the collapsed right lung and a second 1.6 × 1.0 × 1.2 cm pleura-based lesion. The patient was admitted to the hospital and underwent multiple thoracentesis procedures to drain 4.2 liters of fluid. Samples were sent to cytology for analysis.
Review of cytospin preparations of the pleural fluid revealed numerous well-formed spheres of atypical cells. The spheres were composed of relatively large oval to polygonal cells with moderate amounts of cytoplasm surrounding large nuclei with partial chromatic clearing and distinct nucleoli (Figures
(a) Pleural fluid containing multiple spheres of neoplastic cells, Papanicolaou ×400. (b) Cell ball composed of tightly packed atypical oval cells with irregular hyperchromatic nuclei, Papanicolaou ×1000.
A right video-assisted thoracoscopic surgery was performed and the mass biopsied. Histologic evaluation of the biopsy specimen revealed a biphasic tumor characterized by papillary structures and cell nests composed of large polygonal cells with moderate amounts of cytoplasm surrounding large nuclei. The nuclei had a granular to cleared chromatin and distinct nucleoli (Figures
Immunostaining results for large and small cell components of biphasic tumor.
Immunostain | Mesothelial areas | Small blue cell areas |
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MyoD1 | Positive, diffuse | Positive, punctate Golgi |
Manufacturer: Dako | ||
Clone: 5-8A | ||
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CD99 | Positive, diffuse | Positive, punctate Golgi |
Manufacturer: Dako | ||
Clone: MIC2 | ||
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Myogenin | Negative | Negative |
Manufacturer: Dako | ||
Clone: FSD | ||
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CK7 | Positive | Predominantly negative, few focal punctate positive cells |
Manufacturer: Dako | ||
Clone: OV-TL-12/30 | ||
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CK20 | Focal positive | Negative |
Manufacturer: Dako | ||
Clone: Kg20-8 | ||
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TTF-1 | Negative | Negative |
Manufacturer: Leica | ||
Clone: SPT24 | ||
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CK5/6 | Positive, membranous/cytoplasm | Negative |
Manufacturer: Dako | ||
Clone: D5/16 B4 | ||
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Napsin | Negative | Negative |
Manufacturer: Leica | ||
Clone: 1P64 | ||
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Synaptophysin | Negative | Negative |
Manufacturer: Dako | ||
Clone: DAK-Synap | ||
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Chromogranin | Negative | Negative |
Manufacturer: Dako | ||
Clone: DAK-A3 | ||
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LCA (CD45) | Negative | Negative |
Manufacturer: Dako | ||
Clone: 2B11 P07/26 | ||
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D2-40 | Positive | Negative |
Manufacturer: Dako | ||
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Calretinin | Positive | Negative |
Manufacturer: Dako | ||
Clone: Dako-Calret1 | ||
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CK (cocktail) | Positive, membranous | Positive, punctate |
Manufacturer: Dako and Life technologies | ||
Clone: AE1/AE3 and Mak-6 | ||
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A103 | Negative | Negative |
Manufacturer: Dako | ||
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S100 | Negative | Focal positive |
Manufacturer: Dako | ||
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Desmin | Negative | Negative |
Manufacturer: Dako | ||
Clone: D33 | ||
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BCL2 | Negative | Weak positive |
Manufacturer: Dako | ||
Clone: 124 | ||
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CD15 | Negative | Positive, focal punctate |
Manufacturer: Dako | ||
Clone: Carb3 | ||
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PLAP | Negative | Negative |
Manufacturer: Dako | ||
Clone: 8A9 | ||
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HMB45 | Negative | Negative |
Manufacturer: Dako | ||
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CD200 | Positive | Positive |
Manufacturer: R&D systems | ||
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FLI1 | Positive, patchy nuclear | Positive, nuclear |
Manufacturer: BD Bioscience | ||
Clone: G146-222 | ||
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WT1 | Positive, weak nuclear and focal cytoplasmic | Positive, weak nuclear and focal cytoplasmic |
Manufacturer: Biocare Medical | ||
Clone Number: 6F-H2 |
(a) Biphasic tumor with papillary fronds lined by large atypical mesothelial cells, ×200. (b) Neoplastic mesothelial cells with moderate amount of cytoplasm and large nuclei showing partial chromatic clearing and distinct nucleoli, ×600.
(a) The small round cell population arranged in nests of cells with scant cytoplasm and slightly irregular nuclei, ×600. (b) Small cell component with scant cytoplasm and hyperchromatic nuclei containing distinct nucleoli, ×1000.
The small cell component was occasionally associated with a sclerotic stroma, ×400.
(a) Surface mesothelial cell component strongly reactive for calretinin, immunohistochemistry ×400. (b) Both the small cell component and the larger lining cells were reactive with antibodies against CD99, immunohistochemistry ×400.
(a) Small cell component weakly and focally reactive for WT1, immunohistochemistry ×400. (b) Antibodies against FLI1 decorated a component of the small cell population, immunohistochemistry ×200.
A PET/CT examination was performed which confirmed the presence of multiple right sided pleura-based masses, but there was no metastatic disease. The patient agreed to begin Carboplatin/Pemetrexed chemotherapy.
Fluorescence in situ hybridization (FISH) testing was performed on 100 interphase cells from the pleura-based tumor using dual color break-apart probes for 5′
Dual color break-apart FISH probe with only one intact EWSR1 signal in majority of nuclei.
The a-CGH revealed numerous abnormalities. In addition to the loss of heterozygosity (LOH) of 6p and 6q, there were deletions and pathogenic losses on chromosomes 1, 3, 5, 6, 9, 10, 11, 13, 17, 18, 20, and 22 and the distal long arm of the Y chromosome. Table
Pleural tumor chromosomal alterations, cytogenetic band locations, genetic sizes, and the genes involved characterized by a-CGH.
Gain/loss | Chr. | Band | Genomic coordinates | Size (Mb) | # genes involved |
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Loss | 1 | p36.32-p36.13 | chr1: 4762046–19269194 | 14.51 | 176 |
Loss | 1 | p31.3-p21.1 | chr1: 54011592–105928237 | 41.92 | 207 |
Loss | 3 | p22.1-p11.1 | chr3: 41537414–89032174 | 47.49 | 333 |
Loss | 5 | p15.2 | chr5: 10871380–12541595 | 1.67 | 1 |
Loss | 6 | q16.1-q27 | chr6: 95918819–170896238 | 74.98 | 378 |
Loss | 9 | p22.1-p21.2 | chr9: 19296853–26822772 | 7.53 | 36 |
Loss | 9 | q33.2-q34.3 | chr9: 124754535–141048319 | 16.29 | 309 |
Loss | 10 | p13-p12.31 | chr10: 14966878–22520396 | 7.55 | 39 |
Loss | 10 | q23.1-q23.2 | chr10: 82824485–89272483 | 6.45 | 26 |
Loss | 10 | q23.33-q25.1 | chr10: 96270114–108891603 | 12.62 | 153 |
Loss | 10 | q25.3-q26.11 | chr10: 118281211–119246215 | 0.97 | 12 |
Loss | 10 | q26.2-q26.3 | chr10: 127801222–135425200 | 7.62 | 48 |
Loss | 11 | p15.5-p11.12 | chr11: 205172–50406383 | 50.2 | 482 |
Loss | 11 | q11-q13.1 | chr11: 55119736–64516115 | 9.4 | 260 |
Loss | 13 | q21.2-q31.3 | chr13: 62076573–90289382 | 28.21 | 35 |
Loss | 17 | p13.3-p11.2 | chr17: 51885–20317045 | 20.27 | 369 |
Loss | 17 | q11.2 | chr17: 27804400–30770711 | 2.97 | 44 |
Loss | 18 | p11.32-p11.21 | chr18: 118760–15083488 | 14.96 | 78 |
Loss | 18 | q11.1-q23 | chr18: 18526965–78010032 | 59.48 | 227 |
Loss | 20 | q12-q13.13 | chr20: 37642287–48165701 | 10.52 | 109 |
Loss | 20 | q13.33 | chr20: 58988271–60137888 | 1.15 | 1 |
Loss | 22 | q12.1-q13.33 | chr22: 26304781–51224252 | 24.92 | 347 |
Del | Y | q11.221-q12 | chrY: 18548030–58909664 | 40.36 | 56 |
Reverse transcriptase polymerase chain reaction (RT-PCR) was performed at an outside reference laboratory using primers specific for the
Morphologically, our case presented a mixed pattern composed of both a papillary pattern epithelioid mesothelioma and a larger small round cell component. This small cell component raised the possibility of a DSRCT or a small cell predominant mesothelioma as described by Mayall and Gibbs [
The majority of prior reports of small cell mesothelioma describe a micropapillary or tubulopapillary component composed of cells with eosinophilic cytoplasm [
Although exact percentages of immunopositivity vary, DSRCTs are routinely positive for cytokeratin, EMA, NSE, vimentin, and desmin. EMA positivity is seen in greater than 90% of DSRCTs and is the marker of choice for epithelial differentiation [
The immunostaining pattern for mesotheliomas is considerably more straightforward than the complex epithelial, neural, and muscle coexpression in DSRCTs. Although the majority of both DSRCTs and mesotheliomas express WT1, only rarely and weakly do DSRCTs express calretinin [
Immunohistochemical findings in the reported small cell mesothelioma have been variable, but Cha et al. [
There have been several reports of aberrant or unusual DSRCT immunostaining [
Unlike prior studies of small cell mesotheliomas, we were able to perform a number of molecular analyses in our case. These studies were performed to determine whether the small cell component demonstrated features consistent with a primary mesothelioma or a DSRCT. Molecular studies, including FISH or RT-PCR, are designed to detect the recurrent t(11;22)(p13;q12) translocation that generates a
Molecular variants of the
In addition to transcript length variations, two DSRCT cases were examined with FISH by La Starza et al. to reveal multiple copies of the
Regardless of the translocation variant, the presence of the
Numerous cases of mesothelioma have also been subjected to karyotyping and a-CGH. Karyotyping revealed multiple chromosomal numerical changes with more losses than gains [
Because DSRCTs generally express WT1 and are commonly located on peritoneal surfaces like mesotheliomas, authors have attempted to define DSRCTs as “a blastematous tumor derived of primitive mesothelium” [
Our patient’s tumor histologically appeared to have both mesotheliomatous and more primitive looking areas suggestive of desmoplastic small round cell tumor. The biphasic nature was confirmed with immunostaining, the mesothelial area marked with calretinin, WT1, D2-40, CK7, and CK5/6, while the small cell areas were positive for Golgi MyoD1, CD99, CD200, FLI1, and WT1. Interestingly, the cytologic features were characteristic of an epithelial mesothelioma rather than a small cell carcinoma or DSRCT. Although we hoped to confirm the diagnosis of a DSRCT component with FISH and later RT-PCR for the fusion product EWS-WT1, we conclude that the present case represents a small cell mesothelioma with the small cell component focally resembling a DSRCT and in other areas a blastemal-like mesothelioma.
This paper was approved by University of Missouri Institutional Review Board (Project no. 2002193; date of approval: 4/27/15).
The authors declare that there are no competing interests regarding the publication of this paper.
Drs. Lester Layfield and Richard D. Hammer devised list of immunohistochemical stains during the workup of this patient’s tumor and analyzed the PCR and FISH data. Drs. Richard D. Hammer and Sarah Hackman analyzed the microarray data. Dr. Sarah Hackman wrote the paper with input and multiple revisions from both Dr. Richard D. Hammer and Dr. Lester Layfield.