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Bladder
Other tumors
Clear cell myomelanocytic tumor
Author: Nat Pernick, M.D. (see Authors page)
Revised: 23 December 2009, last major update - December 2009
Copyright: (c) 2002-2009, PathologyOutlines.com, Inc.
Definition
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● Mesenchymal tumor composed of histologically and immunohistochemically distinctive perivascular epithelioid cells
● Tumors also arise in falciform ligament/ligamentum teres
● Related to angiomyolipoma, lymphangioleiomyomatosis, clear cell sugar tumor
● Above entities may reflect a continuous spectrum
Terminology
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● Also called PEComa (for Perivascular Epithelioid Cell)
Epidemiology
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● Rare; <20 cases reported in bladder thru 2009
● Median age of 36 years (range, 19 to 48 years), 2/3 male
● Not associated with tuberous sclerosis to date
Sites
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Etiology
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Clinical features
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● 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
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● Proposed classification system for non-angiomyolipoma PEComas:
- Benign: <5 cm in size with low cellularity, low nuclear grade, mitotic rate less than 1/50 high power field, 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: tumors with one atypical feature above (Am J Surg Pathol 2005;29:1558)
Case reports
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● 19 year old woman (Ann Diagn Pathol 2005;9:275)
● 24 year old woman (CUAJ 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)
Treatment
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● Excision; possibly adjuvant therapy
Clinical images
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Gross description (Macroscopy)
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Gross images
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Micro description (Histopathology)
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● Spindled and epithelioid cell morphology with variable clear cell change
● Delicate vasculature stroma
Micro images
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Epithelioid cells with abundant eosinophilic and granular cytoplasm and occasional nuclear inclusions, link
No thumbnail: Soft tissue tumor #1; #2; NKI-C3
MelanA+; Smooth Muscle Actin+; Various stains at various sites
Cytology description
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Cytology images
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Positive stains
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● HMB45 and other melanocytic markers, smooth muscle actin and other smooth muscle markers (smooth muscle staining may be limited / absent in epithelioid tumors)
Negative stains
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● S100
Electron microscopy descriptions
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Electron microscopy images
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Molecular / cytogenetics description
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● Frequent deletion of 16p in which TSC2 gene is located; also other gross chromosomal changes (Hum Pathol 2006;37:606)
Molecular / cytogenetics images
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Differential Diagnosis
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● Clear cell sarcoma of soft parts: collagenous and avascular stroma, frequently has tumor giant cells, 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, negative for melanocytic markers (but may be HMB45+)
● Melanoma: usually melanotic, atypical melanocytes in adjacent mucosa
● Sarcomatoid carcinoma: in situ carcinoma, keratin+, negative for melanocytic markers
● Smooth muscle tumor: fascicles, not packets of cells; more eosinophilic cytoplasm, HMB45-
Additional references
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End of Bladder > Other tumors > Clear cell myomelanocytic tumor
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