Breast nonmalignant
Benign tumors

Topic Completed: 1 August 2012

Revised: 9 September 2019

Copyright 2002-2019,, Inc.

PubMed search: Myofibroblastoma [title] breast [title]

Monika Roychowdhury, M.D.
Page views in 2019: 9,659
Page views in 2020 to date: 3,000
Cite this page: Roychowdhury M. Myofibroblastoma . website. Accessed April 1st, 2020.
Definition / general
  • Also called benign stromal spindle cell tumor with predominant myofibroblastic differentiation
Clinical features
  • Solitary, slow growing nodule
  • Benign behavior
Case reports
  • Excision is curative
Clinical images

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15 cm tumor

Gross description
  • Well circumscribed nodule or multilobar mass
  • Bulging, gray pink and 1 - 4 cm
  • Resembles fibroadenoma
Gross images

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Firm, circumscribed, tan gray lobulated nodule

Microscopic (histologic) description
  • Well circumscribed
  • Uniform, bland spindle cells haphazardly arranged in fascicles with pushing borders, separated by broad bands of hyalinized collagen (Stanford University: Myofibroblastoma of the Breast)
  • 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) and infiltrative (no atypia or mitotic activity)
  • May have histiocytoid cells, prominent vessels, focal cartilaginous differentiation (Virchows Arch 1999;434:547), smooth muscle and multinucleated floret-like giant cells
  • No / rare mitotic activity
  • Usually no entrapment of ducts or lobules
  • Usually no necrosis
Microscopic (histologic) images

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AFIP images

Well circumscribed

Fascicles of spindle cells separated by dense collagen

Case of the Week #395

H&E images




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Epithelioid type

Well circumscribed

Spindle cells and hyalinized collagen

Classic type

Cellular variant

Other variants

Predominantly fatty variant


H&E, CD34, SMA

Fig 1: Sharply circumscribed tumor with fibrous pseudocapsule
Fig 2: Bland spindle cells in collagenous or myxoid stroma
Fig 3A: CD34+; fig 3B: bcl2+
Fig 4: Desmin+ (focal)

Cytology description
  • May appear malignant
  • Cohesive and single spindle cells without atypia
  • Scant cytoplasm and oval nuclei with fine granular chromatin, occasional nuclear grooves and 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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Fig 2: Loose groups of
cells with abundant
eosinophilic granular
cytoplasm and bland nuclei

Negative stains
Electron microscopy description
Molecular / cytogenetics description
Differential diagnosis
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