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