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Pancreas

Other tumors

PEComa

Reviewer: Deepali Jain, M.D. (see Reviewers page)
Revised: 30 November 2012, last major update August 2012
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc.

General
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● Perivascular Epithelioid Cell tumor
● Rare, also called clear cell "sugar" tumor
● Well vascularized neoplasm composed of large, clear, epithelioid smooth muscle cells, HMB45+, MelanA+, smooth muscle actin+, keratin- (WHO)
● Concept first proposed in 1992 (Am J Surg Pathol 1992;16:307)
● Arises from perivascular epithelioid cells, which also cause lymphangioleiomyomatosis, angiomyolipoma (renal and extrarenal, Virchows Arch 2008;452:119), related tumors of falciform ligament / ligamentum teres, skin (Histopathology 2005;46:498), uterus (Mod Pathol 2005;18:1336) and other viscera and soft tissue
● Origin: no known normal counterpart to perivascular epithelioid cell

Case reports
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● 31 year old woman with incidental mass (Virchows Arch 2005;446:555)
● 37 year old woman (Case of the Week #143)
● 49 year old man with incidental mass (JOP 2011;12:55)
● 51 year old woman withmalignant pancreatic PEComa (AIMM 2012 Published Ahead-of-Print)
● 60 year old woman (Am J Surg Pathol 1996;20:722)
● 60 year old woman with abdominal "buldge" (Am J Surg Pathol 1996;20:722)

Micro description
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● Large epithelioid cells, clear or eosinophilic granular cytoplasm containing glycogen with nuclear pleomorphism but no mitotic activity
● May have brown “dusty” pigment suggestive of melanin
● No glandular growth or sarcomatous features
● Malignant appearing tumors may have large zones of necrosis and nests of malignant cells with marked cellular pleomorphism and mitotic activity

Micro images
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Well-vascularized neoplasm composed of epithelioid smooth muscle cells with clear cytoplasm rich in glycogen

   

   
Malignant tumor

 
Left: HMB45, right: actin

   
Left to right: Well-demarcated tumor adjacent to normal pancreas (left-lower corner); tumor is composed of sheets of epithelioid to spindled cells with abundant clear to granular cytoplasm, and mild to moderate nuclear pleomorphism; MelanA+; SMA+

Positive stains
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● HMB45, MelanA, smooth muscle actin (Int J Surg Pathol 2010;18:243)
● Also CD1a (Pathol Int 2008;58:169), variable EMA, variable S100

Negative stains
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● Cytokeratin, CD68, CD45, CD117, NSE, chromogranin A, lipase, amylase, inhibin

Electron microscopy description
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● Membrane bound granules
● Typical melanosomes or premelanosomes and aberrant melanosomes (Pathol Int 2009;59:650, Ultrastruct Pathol 2012;36:124)

Differential diagnosis
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● Recommended to thoroughly sample tumor, use melanocytic markers and other immunostains, possibly molecular markers
● Clear cell carcinoma
● Also alveolar soft part sarcoma, clear cell sarcoma of soft parts, GIST, leiomyosarcoma, melanoma, paraganglioma (Am J Surg Pathol 2009;33:475)

End of Pancreas > Other tumors > PEComa

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