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Other tumors

Perivascular epithelioid cell tumor (PEComa)

Reviewers: Turki Al-Hussain, M.D., Johns Hopkins Medical Centers (see Reviewers page)
Revised: 24 March 2011, last major update March 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.


● Mesenchymal tumor composed of histologically and immunohistochemically distinctive perivascular epithelioid cells that are immunoreactive for melanocytic markers
● The PEComa family includes more common tumors such as angiomyolipoma (AML), clear-cell ("sugar") tumor of the lung and lymphangioleiomyoma, as well as less common tumors of the falciform ligament/ligamentum teres, bone, soft tissue and skin (Am J Surg Pathol 2009;33:304)


● Also called clear cell myomelanocytic tumor


● Rare; <20 cases reported in bladder thru 2009
● Median age 36 years (range, 19 to 48 years), 2/3 male
● Not associated with tuberous sclerosis to date

Clinical features

● Most reported cases (at various sites) have benign behavior (Am J Surg Pathol 2009;33:304, but see Virchows Arch 2007;450:463)

Prognostic factors

Proposed classification system for non-angiomyolipoma PEComas:
Benign: <5 cm in size with low cellularity, low nuclear grade, mitotic rate less than 1 per 50 high power fields and no infiltration, necrosis or vascular invasion
Malignant: tumors that show 2 or more of the following features: size greater than 5 cm, infiltrative growth pattern, high mitotic rate, pleomorphism, necrosis or vascular invasion
Uncertain malignant potential: Only "malignant" feature is either nuclear pleomorphism / multinucleated giant cells or size >5 cm (Am J Surg Pathol 2005;29:1558)

Case reports

● 19 year old woman (Ann Diagn Pathol 2005;9:275), 23 year old man (Ann Diagn Pathol 2010 Oct 30 [Epub ahead of print], 24 year old woman (Can Urol Assoc J 2008;2:230)
● 33 year old woman with incidental bladder tumor in muscularis propria (Am J Surg Pathol 2003;27:689), 48 year old man treated with excision and alpha-interferon (BMC Urol 2006 Aug 22;6:20)


● Excision; possibly adjuvant therapy


● Spindled and epithelioid cells with variable clear cell change
● Delicate vasculature stroma

Micro images

Epithelioid cells with abundant eosinophilic and granular cytoplasm and occasional nuclear inclusions

Various sites             MelanA+

Smooth muscle actin+; various stains at various sites

Other images: soft tissue tumor #1; #2; NKI-C3

Positive stains

● HMB45, MelanA/Mart-1 and other melanocytic markers
● Smooth muscle actin and other smooth muscle markers (smooth muscle staining may be limited / absent in epithelioid tumors)

Negative stains

● S100


● Frequent deletion of 16p in which TSC2 gene is located
● Also other gross chromosomal changes (Hum Pathol 2006;37:606)

Differential diagnosis

Clear cell sarcoma of soft parts: collagenous and avascular stroma, frequently has tumor giant cells, S100+, actin-
Inflammatory myofibroblastic tumor: chronic inflammation, myxoid change, ALK1+ or ALK fusion
Leiomyosarcoma: diffuse cytoplasmic eosinophilia, perinuclear vacuoles, cigar shaped nuclei, prominent thick walled vessels, usually negative for melanocytic markers (but may be HMB45+)
Melanoma: usually melanotic, atypical melanocytes in adjacent mucosa, S100+, negative for muscle markers
Sarcomatoid carcinoma: in situ carcinoma present, keratin+, negative for melanocytic markers
Other smooth muscle tumors: fascicles, not packets of cells; more eosinophilic cytoplasm, HMB45-
GIST: no delicate vasculature stroma, HMB45-, CD34+, CD117+ (but PEComa can also be CD117+)

End of Bladder > Other tumors > Perivascular epithelioid cell tumor (PEComa)

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