Review of Myofibroblastoma of Breast and Its Most Common Mimickers

Ying Huang, MD, PhD, Frank Chen, MD, PhD


Myofibroblastoma (MFB) is characterized as a benign stromal neoplasm composed of uniform, bland-looking spindle cells that are often arranged in fascicles separated by thick band of collagenous stroma.  Variable cellularity is common.  Immunohistochemically, the spindle cells are positive for CD34, vimentin, BCL-2, ER, PR, focally positive for smooth muscle actin and negative for cytokeratin, S-100 and CD117.  Although classic MFB is typically a bland-looking spindle cell tumor, some unusual morphologic variants may show worrisome malignant-looking cells. Recognition of MFB variants and its wide variety of mimickers is very important for pathologists to arrive at the correct diagnosis, and avoid misdiagnosis of malignancy.


breast, myofibroblastoma, solitary fibrous tumor, spindle cell lipoma, metaplastic spindle cell carcinoma, myofibroblastic sarcoma, Phyllodes tumor

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