Myofibroblastoma of the breast with diverse differentiations

Abstract

Background: The histogenesis of myofibroblastoma of the breast remains unknown.

Design: Two cases of myofibroblastoma of the female breast were analyzed using light microscopy and immunohistochemistry.

Results: The tumors were well circumscribed and predominantly composed of bland bipolar spindle cells and interspersed bands of hyalinized collagen. Additionally, one tumor contained a cartilaginous island, and the other contained a well-defined small nodule that consisted of fascicular arrangements of mitotically inactive atypical cells, simulating atypical leiomyoma. Both lesions contained a fatty element. Immunohistochemically, spindle tumor cells expressed desmin, alpha-smooth muscle actin, muscle actin, and CD34. The atypical cells were strongly and diffusely positive for all these markers. Both tumors were DNA diploid and had a moderate S-phase fraction. The patients have no evidence of disease 4 and 18 months after simple excision.

Conclusions: Myofibroblastoma of the breast may be a benign mesenchymal neoplasm capable of diverse lines of differentiation.