Myofibroblastoma (MFB) of the breast is an uncommon but well described benign stromal neoplasm of the breast. MFB can have many different morphologic patterns (see variants below), but important defining characteristics include:
- Mesenchymal tumor without epimyoepithelial elements
- No necrosis
- Low proliferative activity (≤2 mitoses/10 hpf)
- No atypical mitoses
- Characteristic immunophenotype
Immunohistochemisty of MFB
- CD34: Positive
- Desmin: Positive
- Vimentin: Positive
- Bcl-2, SMA, & CD99: Often positive but may have intratumoral variabliity
- Cytokeratin, S-100, EMA, HMB-45, CD117: Negative
Morphologic Variants
- Classic type
- Myxoid
- Epithelioid
- Collagenized/fibrous
- Infiltrative
- Lipomatous
- Cellular
- Deciduoid-like
Photomicrographs
References
Magro G. Mammary myofibroblastoma: a tumor with a wide morphologic spectrum. Arch Pathol Lab Med. 2008;132: 1813–1820. doi:10.1043/1543-2165-132.11.1813
Mele M, Jensen V, Wronecki A, Lelkaitis G. Myofibroblastoma of the breast: Case report and literature review. Int J Surg Case Rep. 2011;2: 93–96. doi:10.1016/j.ijscr.2011.02.006