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Surgical Pathology Criteria

Myofibroblastoma of the Breast


  • Benign circumscribed spindle cell neoplasm of the breast exhibiting myofibroblastic differentiation

Alternate/Historical Names

  • Benign spindle stromal tumor of the breast

Diagnostic Criteria

  • Fascicles of spindle cells partially separated by bands of hyalinized collagen
    • Haphazard short fascicles of cells
    • Uniform bland short spindle cells
      • Oval nuclei
      • Slightly irregular nuclear membrane
      • 1 or 2 small nucleoli
      • Occasional nuclear grooves
      • Moderate amount of pale to eosinophilic cytoplasm
    • Infrequent mitotic figures (0-2/10 hpf)
  • Collagen bundles range from sparse to prominent
    • Often arranged as thin strips
    • Stroma occasionally myxoid
  • Sharply circumscribed
    • Surrounding pseudocapsule
    • No epithelial elements within lesion
  • Variable features
    • Fat lobules occasional to prominient
    • Rare multinucleated cells in some cases
    • One case with focal cartilaginous differentiation
  • Variable reactivity for desmin, actin and CD34
  • It has been proposed that in the breast, myofibroblastoma forms a spectrum with spindle cell lipoma and solitary fibrous tumor (Magro 2002)
  • Similar lesion has been reported as "mammary-type myofibroblastoma of soft tissue" (McMenamin 2001)

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting:: May 1, 2006

Supplemental studies


Desmin Focal to strong
Smooth muscle actin focal
CD34 Positive
CD99 Positive
bcl2 Positive
Vimentin Positive
S100 Negative
Keratin Negative

Genetic analysis

  • One report of partial monosomy 13q and 16q
  • Similar to chromosomal aberrations seen in spindle cell lipoma

Differential Diagnosis

Myofibroblastoma of the Breast Fibromatosis of the Breast
Circumscribed border Infiltrative
Moderate amount of cytoplasm Scant cytoplasm
No epithelial elements within lesion Often contains epithelial elements


Myofibroblastoma of the Breast Nodular Fasciitis of the Breast
Circumscribed border Not circumscribed
Hyalinized bundles of collagen Predominantly myxoid stroma
Mitotic figures rare Frequent mitotic figures
Undulating fascicles Short disrupted C or S shaped fascicles


Myofibroblastoma Schwannoma
Short disrupted fascicles Both Antoni A and B patterns
S100 negative S100 positive
Actin and desmin may be positive Actin and desmin negative


Myofibroblastoma of the Breast Leiomyoma
Short disrupted fascicles Long fascicles
Smooth muscle actin not extensive Smooth muscle actin extensive


Myofibroblastoma of the Breast Metaplastic Carcinoma of the Breast
Circumscribed border Infiltrative
Cytologically bland Usually has cytologically atypical areas
No epithelial component Frequently has epithelial component
Keratin negative May be keratin positive


Myofibroblastoma of the Breast Primary Sarcoma of the Breast
Circumscribed border Infiltrative
Cytologically bland Cytologically atypical


Myofibroblastoma of the Breast Spindle Cell Lipoma
Desmin and actin usually positive Desmin and actin negative
Some have proposed that these may be related


Myofibroblastoma Pseudoangiomatous Stromal Hyperplasia
Uniformly cellular Even cellular lesions have classical paucicellular areas
No epithelial elements within lesion Typically surrounds ducts and lobules
At the cellular end of the spectrum, PASH shows many features of myofibroblastoma and the pseudovascular spaces may be obscured; the two are probably morphologic variants of the same lesion


Myofibroblastoma Adenomyoepithelioma
No epithelial component Tubules integral to lesion
Stromal keratin negative, CD34 positive, muscle/myoid markers variable Stromal keratin variable, p63 and muscle/myoid markers positive


  • Male:Female = approximately 2:1
  • Age 41-85
  • Size 1-3.7 cm
  • Single freely movable mass
  • Most parenchymal, one subareolar
  • No recurrences or metastases if excised


Breast Tumors and Lesions Exhibiting Reactivity for Muscle/Myoepithelial Markers

(Most benign lesions with an epithelial component will have a myoepithelial cell layer)


  • Wargotz ES, Weiss SW, Norris HJ. Myofibroblastoma of the breast. Sixteen cases of a distinctive benign mesenchymal tumor. Am J Surg Pathol. 1987 Jul;11(7):493-502.
  • Brogi E. Benign and malignant spindle cell lesions of the breast. Semin Diagn Pathol. 2004 Feb;21(1):57-64.
  • Magro G, Bisceglia M, Michal M, Eusebi V. Spindle cell lipoma-like tumor, solitary fibrous tumor and myofibroblastoma of the breast: a clinico-pathological analysis of 13 cases in favor of a unifying histogenetic concept. Virchows Arch. 2002 Mar;440(3):249-60.
  • McMenamin ME, Fletcher CD. Mammary-type myofibroblastoma of soft tissue: a tumor closely related to spindle cell lipoma. Am J Surg Pathol. 2001 Aug;25(8):1022-9.
  • Pauwels P, Sciot R, Croiset F, Rutten H, Van den Berghe H, Dal Cin P. Myofibroblastoma of the breast: genetic link with spindle cell lipoma. J Pathol. 2000 Jul;191(3):282-5.
  • Lee AH, Sworn MJ, Theaker JM, Fletcher CD. Myofibroblastoma of breast: an immunohistochemical study. Histopathology. 1993 Jan;22(1):75-8.
  • Gocht A, Bosmuller HC, Bassler R, Tavassoli FA, Moinfar F, Katenkamp D, Schirrmacher K, Luders P, Saeger W. Breast tumors with myofibroblastic differentiation: clinico-pathological observations in myofibroblastoma and myofibrosarcoma. Pathol Res Pract. 1999;195(1):1-10.
  • Magro G, Michal M, Vasquez E, Bisceglia M. Lipomatous myofibroblastoma: a potential diagnostic pitfall in the spectrum of the spindle cell lesions of the breast. Virchows Arch. 2000 Nov;437(5):540-4.
  • Eyden BP, Shanks JH, Ioachim E, Ali HH, Christensen L, Howat AJ. Myofibroblastoma of breast: evidence favoring smooth-muscle rather than myofibroblastic differentiation. Ultrastruct Pathol. 1999 Jul-Aug;23(4):249-57.
  • Fukunaga M, Ushigome S. Myofibroblastoma of the breast with diverse differentiations. Arch Pathol Lab Med. 1997 Jun;121(6):599-603.
  • Thomas TM, Myint A, Mak CK, Chan JK. Mammary myofibroblastoma with leiomyomatous differentiation. Am J Clin Pathol. 1997 Jan;107(1):52-5.
  • Damiani S, Miettinen M, Peterse JL, Eusebi V. Solitary fibrous tumour (myofibroblastoma) of the breast. Virchows Arch. 1994;425(1):89-92.
  • Julien M, Trojani M, Coindre JM. [Myofibroblastoma of the breast. Report of 8 cases] Ann Pathol. 1994;14(3):143-7. French.
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