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). Th
ey were composed of cells with a spectrum of appearances including sma
ll, compact cells, spindle cells, large histiocytoid cells, and epithe
lioid cells. All had broad bands of dense collagen, and adipose tissue
was present in seven tumors. Foci of pseudoangiomatous hyperplasia we
re present in two cases. Strong vimentin positivity was present in sev
en tumors, which were cytokeratin negative. Weak S100 positivity was d
emonstrated in one lesion, and actin was positive in two lesions. Desm
in was positive in six tumors and negative in one tumor. Treatment for
all of the patients was excisional biopsy. Follow-up, available in fi
ve cases, was from 10 months to 6 years, 11 months (mean, 37 mo; media
n, 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 myofibrobla
sts. Excisional biopsy is adequate therapy.