Surgical Pathology Criteria–

Myofibroblastoma of the Breast

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

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