Breast Myofibroblastoma

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

Myofibroblastoma - CD34 — CD34 expression in a myofibroblastoma.

Myofibroblastoma - Desmin — Strong desmin expression in a myofbiroblastoma

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