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Breast-nonmalignant
Benign (usually) tumors / changes
Myofibroblastoma of breast
Author: Nat Pernick, M.D. (see Authors page)
Revised: 13 March 2010, last major update March 2010
Copyright: (c) 2002-2010, PathologyOutlines.com, Inc.
Definition
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● Rare benign spindle cell tumor of mammary stroma composed of myofibroblasts
● First described in 1987 (AJSP 1987;11:493)
Terminology
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● Also called benign stromal spindle cell tumor with predominant myofibroblastic differentiation
Epidemiology
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● Although initially considered male predominant, now equal gender frequency (older men and post-menopausal women)
● Incidence appears to be increasing, but probably an artifact of mammographic screening (Arch Pathol Lab Med 2008;132:1813)
Sites
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●
Etiology
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● May derive from CD34+/vimentin+ fibroblasts of mammary stroma capable of multidirectional differentiation (Histopathology 2003;42:233)
● Probably related to spindle cell lipoma and solitary fibrous tumor (Virchows Arch 2002;440:249, AJSP 2001;25:1022, Breast J 2008;14:287)
Clinical features
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● Solitary, slow growing nodule
● Benign behavior
Case reports
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● 25 year old man with bilateral gynecomastia (Int J Surg Pathol 2001;9:331)
● 40 year old woman (Indian J Pathol Microbiol 2008;51:395)
● 59 year old woman with breast nodule (University of Pittsburgh, Case #249)
● 65 year old man with 15 cm rapidly growing tumor (J Med Case Reports 2008;2:157)
● 72 year old man with well circumscribed mass (Archives 2003;127:e415)
● 83 year old man with 10 cm tumor (AJSP 1994;18:1170)
● Post-radiation tumor (Breast J 1999;5:136)
Treatment
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● Excision is curative
Clinical images
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Very large breast tumor in man
Gross description (Macroscopy)
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● Well circumscribed nodule or multilobar mass
● Bulging, gray-pink, 1-4 cm
● Resembles fibroadenoma
Gross images
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Firm, circumscribed tan-gray lobulated nodule
Micro description (Histopathology)
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● Well circumscribed
● Uniform, bland spindle cells haphazardly arranged in fascicles with pushing borders, separated by broad bands of hyalinized collagen
● Spindle cells have abundant eosinophilic cytoplasm, round/oval nucleus with 1-2 small nucleoli
● May have mild nuclear pleomorphism
● Prominent mast cells
● Variants include cellular, collagenized, epithelioid (Am J Surg Pathol 2009;33:1085), fatty (J Clin Pathol 2001;54:568), infiltrative (no atypia or mitotic activity)
● May have histiocytoid cells, prominent vessels, focal cartilaginous differentiation (Virchows Arch 1999;434:547), smooth muscle, multinucleated floret-like giant cells
● No / rare mitotic activity
● Usually no entrapment of ducts or lobules
● Usually no necrosis
Micro images
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Well circumscribed Spindle cells and hyalinized collagen
Fascicles of spindle cells separated by dense collagen
Classic type Cellular variant Other variants
AFIP Fig 491: circumscribed border Various images
Epithelioid type
Predominantly fatty variant: H&E and desmin
CD34+
Fig 1: sharply circumscribed tumor with fibrous pseudocapsule
Fig 2: composed of bland spindle cells in collagenous or myxoid stroma
Fig 3A: CD34+
Fig 3B: bcl2+
Fig 4: desmin+ (focal)
Virtual Slides
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Videos
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Cytology description
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● May appear malignant
● Cohesive and single spindle cells without atypia
● Scant cytoplasm and oval nuclei with fine granular chromatin, occasional nuclear grooves, small nucleoli (Diagn Cytopathol 2004;30:406)
● Tumor cells may be intimately associated with extracellular matrix material
● Also mast cells, hyaline bands between tumor cells (Diagn Cytopathol 2002;26:290)
● May have features of solitary fibrous tumor or pleomorphic lipoma (Pathol Res Pract 1999;195:257)
Cytology images
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Loose groups of cells with abundant eosinophilic granular cytoplasm and bland nuclei
Positive stains
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● ER, PR (Histopathology 2000;36:515), vimentin, CD34 (often)
● bcl2
● Variable desmin, caldesmon and androgen receptors (Hum Path 1998;29:347)
Negative stains
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● S100, cytokeratin
● Ki-67 (or low)
Electron microscopy descriptions
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● Features of smooth muscle and myofibroblasts: rough endoplasmic reticulum, bundles of myofilaments with focal densities, intermediate filaments, attachment plaques (Ultrastruct Pathol 1999;23:249, Pathol Res Pract 1999;195:1)
Electron microscopy images
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Molecular / cytogenetics description
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● 13q-, 16q- (similar to spindle cell lipoma, J Pathol 2000;191:282)
Molecular / cytogenetics images
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Differential Diagnosis
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● Fibromatosis: not circumscribed, more diffuse fibrosis, no thick bands of collagen
● Nodular fasciitis: more infiltrative, mucoid stroma
● Myoepithelioma: S100+, keratin+
● Myofibrosarcoma: marked cellular pleomorphism, infiltrating margins and high mitotic rate
● Solitary fibrous tumor: negative for desmin and actin (Breast 2001;10:49), but see article above under Etiology suggesting that these tumors are part of the same spectrum of disease
Additional references
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● Mod Path 1996;9:786 (female patients), Stanford University
End of Breast-nonmalignant > Benign (usually) tumors / changes > Myofibroblastoma
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