Uncommon presentation of mammary myofibroblastoma.

Myofibroblastoma, a rare benign mesenchymal mammary neoplasm, has been diagnosed largely in men as a unilateral, solitary lesion. We studied nine examples occurring in the breasts of eight patients, all but one of whom were women. In the man, the lesions were bilateral. Patients ranged in age from 44 to 67 years (mean and median, 55 yr). The tumors were well circumscribed and measured 0.9 to 3.0 cm (mean, 1.5 cm). They were composed of cells with a spectrum of appearances including small, compact cells, spindle cells, large histiocytoid cells, and epithelioid cells. All had broad bands of dense collagen, and adipose tissue was present in seven tumors. Foci of pseudoangiomatous hyperplasia were present in two cases. Strong vimentin positivity was present in seven tumors, which were cytokeratin negative. Weak S100 positivity was demonstrated in one lesion, and actin was positive in two lesions. Desmin was positive in six tumors and negative in one tumor. Treatment for all of the patients was excisional biopsy. Follow-up, available in five cases, was from 10 months to 6 years, 11 months (mean, 37 mo; median, 63 mo). All patients are alive and without evidence of disease. The clinical and pathologic characteristics of myofibroblastoma in women are similar to published data on the tumor in men. The tumors exhibit heterogeneous immunoreactivity for markers associated with myofibroblasts. Excisional biopsy is adequate therapy.