Benign tumors / changes
Myofibroblastoma of breast

Authors: Monika Roychowdhury, M.D. (see Authors page)

Revised: 21 July 2016, last major update August 2012

Copyright: (c) 2001-2016,, Inc.

PubMed search: Myofibroblastoma[title] breast
Cite this page: Myofibroblastoma of breast. website. Accessed March 29th, 2017.
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

Micro Description
  • Well-circumscribed
  • Uniform, bland spindle cells haphazardly arranged in fascicles with pushing borders, separated by broad bands of hyalinized collagen (Stanford University)
  • 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
Micro Images

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Case of the Week #395:

H&E images




Well circumscribed

Fascicles of spindle cells separated by dense collagen

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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
Molecular / Cytogenetics Description
Electron Microscopy Description
Differential Diagnosis