Mammary-Type Myofibroblastoma: A Report of Two Cases

Mammary-type myofibroblastoma (MFB) is a rare, benign spindle cell neoplasm occurring along the milkline, with extension from the mid-axilla to the medial groin. It is histologically and immunohistochemically identical to MFB of the breast and is part of a spectrum of lesions that includes spindle cell lipoma and cellular angiofibroma. Recently, we experienced two cases of mammary-type MFB involving male patients aged 30 and 58 years, respectively. The tumors were located in the right scrotal sac and in the right axilla. Wide excisions were performed. Microscopically, the masses were composed of haphazardly arranged, variably sized fascicles of bland spindle cells and were admixed with mature fat tissue. The spindle cells in both cases showed immunopositivity for desmin and CD34 and negativity for smooth muscle actin. Loss of retinoblastoma (RB)/13q14 loci is a characteristic genetic alteration of mammary-type MFB, and we identified loss of RB protein expression by immunohistochemical staining. We emphasize the importance of awareness of this rare neoplasm when a spindle cell neoplasm is accompanied by desmin immunopositivity. The second patient was alive without recurrence for 20 months, and the first patient had not been followed.

Epithelioid Myofibroblastoma of Mammary-type in Chest Wall: A Case Report

Mammary-type myofibroblastoma of the soft tissue is a benign mesenchymal tumor, and it is a recently established clinical entity. We report a case of myofibroblastoma of the chest wall with a prominent epithelioid feature, that occurred in a 12-year old female. Although the lesion occurred in the breast area, there was no breast parenchyma in or around the mass, which favored soft tissue of the chest wall origin. The tumor was immunohistochemically identical to the mammary-type myofibroblastoma with diffuse and strong positivity against CD34 and desmin. The myoepithelial differentiation of the tumor was further supported by the electron microscopic analysis. This case indicates that mammary-type myofibroblastoma can occur in a young girl. The mammary-type myofibroblastoma should be considered a differential diagnosis, among epithelioid soft tissue neoplasms in the chest wall when the proper immunohistochemical work-up is done.